Take A Free API 510 Exam Practice Test with Study Guide

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The API Single Certification Programs are well respected and demanded globally in the oil, gas, and petroleum industries. This Quick Study Guide is unique as it is providing simple, accessible and well-structured guidance for anyone studying the API 510 Certified Pressure Vessel Inspector syllabus

API 510 Practice Test or Exam Training Course Certified Pressure Vessel Inspector Syllabus Contents:

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 1: Interpreting ASME and API Codes

  • 1.1      Codes and the real world
  • 1.2      ASME construction codes
  • 1.3      API inspection codes
  • 1.4      Code revisions
  • 1.5      Code illustrations
  • 1.6      New construction versus repair activity
  • 1.7      Conclusion: interpreting API and ASME codes

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 2: An Introduction to API 510 (Sections 1–4)

  • 2.1      Introduction
  • 2.2      Section 1: scope
  • 2.3      Section 3: definitions
  • 2.4      Section 4: owner/user/inspection organizations
  • 2.5      API 510 sections 1–4 familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 3 : API 510 Inspection Practices (Section 5)

  • 3.1      Introduction to API 510 section 5: inspection practices
  • 3.2      Inspection types and planning
  • 3.3      Condition monitoring locations (CMLs)
  • 3.4      Section 5.8: pressure testing
  • 3.5      API 510 section 5 familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 4: API 510 Frequency and Data Evaluation (Sections 6 and 7)

  • 4.1      Introduction
  • 4.2      The contents of section 6
  • 4.3      API 510 section 6 familiarization questions
  • 4.4      Section 7: inspection data evaluation, analysis and recording
  • 4.5     API 510 section 7 familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 5: API 510 Repair, Alteration, Re-rating (Section 8)

  • 5.1      Definitions
  • 5.2      Re-rating
  • 5.3      Repairs
  • 5.4      API 510 section 8 familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 6: API 572 Inspection of Pressure Vessels

  • 6.1      API 572 introduction
  • 6.3      API 572 Section 4.3: materials of construction
  • 6.4      API 572 sections 5, 6 and 7
  • 6.6      API 572 section 9: frequency and time of inspection
  • 6.7      API 572 section 10: inspection methods and limitations
  • 6.8      API 572 section 10 familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 7: API 571 Damage Mechanisms

  • 7.1      API 571 introduction
  • 7.2      The first group of DMs
  • 7.3      API 571 familiarization questions (set 1)
  • 7.4      The second group of DMs
  • 7.5      API 571 familiarization questions (set 2)
  • 7.6      The third group of DMs

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 8: API 576 Inspection of Pressure-Relieving Devices

  • 8.1      Introduction to API 576
  • 8.2      API 576 sections 3 and 4: types (definitions) of pressure-relieving devices
  • 8.3      Types of pressure-relieving device
  • 8.4      API 576 section 5: causes of improper performance
  • 8.6      API 576 familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 9: ASME VIII Pressure Design

  • 9.2      How much of ASME VIII is in the API 510 syllabus?
  • 9.3      ASME VIII clause numbering
  • 9.4      Shell calculations: internal pressure
  • 9.5      Head calculations: internal pressure
  • 9.6      Set 1: shells/heads under internal pressure familiarization questions
  • 9.7      ASME VIII: MAWP and pressure testing
  • 9.8      Set 2: MAWP and pressure testing familiarization questions
  • 9.9      External pressure shell calculations
  • 9.10    Set 3: vessels under external pressure familiarization questions
  • 9.11    Nozzle design

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 10: ASME VIII Welding and NDE

  • 10.1    Introduction
  • 10.3    UW-12: joint efficiencies
  • 10.4    UW-11: RT and UT examinations
  • 10.5    UW-9: design of welded joints
  • 10.6    ASME VIII section UW-11 familiarization questions (set 1)
  • 10.7    Welding requirements of ASME VIII section UW-16
  • 10.8    ASME VIII section UW-16 familiarization questions (set 2)
  • 10.9    RT requirements of ASME VIII sections UW-51 and UW-52
  • 10.10  ASME VIII section UW-51/52 familiarization questions (set 3)

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 11: ASME VIII and API 510 Heat Treatment

  • 11.1    ASME requirements for PWHT
  • 11.2    What is in UCS-56?
  • 11.3    API 510 PWHT overrides
  • 11.4    ASME VIII sections UCS-56 and UW-40: PWHT familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 12: Impact Testing

  • 12.1    Avoiding brittle fracture
  • 12.2    Impact exemption UCS-66
  • 12.3    ASME VIII section UCS-66: impact test exemption familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 13: Introduction to Welding/API 577

  • 13.1    Module introduction
  • 13.2    Welding processes
  • 13.3    Welding consumables
  • 13.4    Welding process familiarization questions
  • 13.5    Welding consumables familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 14: Welding Qualifications and ASME IX

  • 14.1    Module introduction
  • 14.3    Welding documentation reviews: the exam questions
  • 14.4    ASME IX article I
  • 14.5    Section QW-140 types and purposes of tests and examinations
  • 14.6    ASME IX article II
  • 14.7    ASME IX articles I and II familiarization questions
  • 14.8    ASME IX article III
  • 14.9    ASME IX article IV
  • 14.10  ASME IX articles III and IV familiarization questions
  • 14.11  The ASME IX review methodology
  • 14.12  ASME IX WPS/PQR review: worked example

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 15: The NDE Requirements of API 510 and API 577

  • 15.2    API 510 NDE requirements

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 16: NDE Requirements of ASME V

  • 16.1    Introduction
  • 16.3    ASME V article 2: radiographic examination
  • 16.4    ASME V article 6: penetrant testing (PT)
  • 16.5    ASME V articles 1, 2 and 6: familiarization questions
  • 16.7    ASME V article 23: ultrasonic thickness checking
  • 16.8    ASME V articles 7 and 23 familiarization questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 17: Thirty Open-Book Sample Questions

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 18 Answers

  • 18.1    Familiarization answers
  • 18.2    Open-book sample questions answers

Click Here to Read and Take a Practice Test of API 510 Exam Chapter 19: The Final Word on Exam Questions

  • 19.1    All exams anywhere: some statistical nuts and bolts for non-mathematicians
  • 19.2    Exam questions and the three principles of whatever (the universal conundrum of randomness versus balance)
  • 19.3    Exam
  • 19.4    selectivity

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API 510 Chapter 19

API 510 Chapter 19 – The Final Word on Exam Questions

19.1 All exams anywhere: some statistical nuts and bolts for non-mathematicians

The statistiscs of exam questions are unlikely to tax the brains of eminent statisticians for very long. Let’s say we want to choose 150 questions randomly from a set of, say, 900 if that’s how many we have. Now take one question, the classic query about, among other things, how many angels can realistically be persuaded to dance on the head of a pin. Let’s call this, for convenience, question P (P for pin). Every so often, when choosing the question set for our exam, question P will no doubt appear; but how often?

Take the first exam cycle; if we choose 150 questions truly randomly from one large set of 900, then the chance of our question P appearing in the exam is precisely 150/900 or 1 in 6 (or 16.67 % if you like). Put another way, over time it will appear once in every six exams. This means, of course, that if you keep on taking the exam again and again, five times out of every six any effort you have put into remembering the answer to question P (the answer is 14 incidentally) will have been totally wasted.

But hold on; the situation has changed. You now know the answer, so we want it to appear next time. At the next exam cycle, the chances of P appearing are once again 16.67 (but the cumulative probability of the two successive appearances, given that it already had only a 16.67 % of appearing last time) are much less . . . let’s say 1 in 36. Extending this out, the probability of P turning up in three successive exam cycles are getting pretty thin and in four successive cycles, miniscule at best. The odds against you are awful . . . it’s looking like your valuable knowledge of the P answer will most of the time be wasted.

Just when you thought things were looking bad . . . it gets 301 worse. Waiting in the wings is another question Q, to which you already know the answer (it’s the one about the length of the piece of string). It would be nice if this appeared regularly, so you could confidently tick the correct answer box marked 17 inches. Even better, what if both P and Q appeared in every exam draw now you could get them both right. What’s the chance of this?

  • The probability of P and Q both appearing in the first draw are small – we know that .
  • In the first and second draw, an order of magnitude smaller .
  • In the first, second and third draws . . . . undeniably tiny .
  • And, in the first, second, third and fourth draws . . . miniscule would be the operative word

Extending this out to say, five questions, P, Q, R, S and T, that you are certain of the answer, the chances of all five appearing in three successive draws are so near zero that the calculation would be enough to leave your calculator a blackened ruin.

But wait . . . if, by some stretch of the imagination, such a thing did actually happen, you would have to conclude that either these lottery-type odds had occurred or that there was maybe some other explanation. But what could it be?

Working the maths backwards would tell us that we could only be certain to get such a run of unlikely probabilities if we had not 900 questions to choose from at all but a significantly smaller set. This is the much-reduced set size we would need if we were still drawing 150 purely at random from one big set and our five questions P, Q, R, S and T all miraculously appeared in each of three successive draws. That’s one possibility.

There’s another way to do it. If we divide our bank of 900 questions into, say, 10 sets of 90 questions each, based on subject breakdown, and let’s say our exam draw will require that we draw 15 questions from each set to give us the 150- question draw. If our favourite questions P, Q, R, S and T each reside in a different set (which they will, as they are about different subjects), then the odds of all five appearing in three successive draws are reasonably believable, with a little imagination at least. Adding some regular preferences within each set would reduce the odds even further.

In the final act, with a little biasing towards certain questions in each small set our question-drawing exercise will throw off its mask of randomness and, right on cue, up will pop our P, Q, R, S, T combination with a flourish, like the demon king among a crowd of pantomime fairies.

So if you ever see this, the explanation may be one of the options above.

19.2 Exam questions and the three principles of whatever (the universal conundrum of randomness versus balance)

As with most engineering laws and axioms (pretend laws) you won’t get far without a handful of principles (of whatever).

The first principle (of whatever) is that, faced with the dilemma between randomness and balance, any set of exam questions is destined to end up with a bit of both. A core of balance (good for the technical reputation of the whole affair) will inevitably be surrounded by a shroud of some randomness, to pacify the technically curious, surprise the complacent and frustrate the intolerant – in more or less equal measure. There is nothing wrong with this; the purpose of any exam programme must be to weed out those candidates who are not good enough to pass.

Now we have started, the first principle spawns, in true Newtonian fashion, the second principle – a strategy for dealing with the self-created problems of the first. The problem is the age-old one of high complexity. Code documents contain tens of thousands of technical facts, each multifaceted, and together capable of being assembled into an almost infinite set of exam questions. We need some way to deal with this. The second principle becomes: selectivity can handle this complexity.

Tightening this down, we get the third principle: only selectivity can handle this complexity. There’s nothing academic about the third principle (of whatever); it just says that if you try to memorize and regurgitate, brightly coloured parrot-fashion, all the content of any exam syllabus, you are almost guaranteed to fail. You will fail because most of the time the high complexity will get you. It has to, because exam questions can replicate and mutate in almost infinite variety, whereas you cannot. You may be lucky (who doesn’t need a bit of luck?) but a more probable outcome is that you will be left taking the exam multiple times. Round and round and round you will go at your own expense, clawing at the pass/fail interface.

A quick revisit of the first principle (of whatever) suggests that being selective in the parts of an exam syllabus we study carries with it a certain risk. The price for being selective is that you may be wrong. Most of the risk has its roots in the amount of balance versus randomness that exists in the exam set. The more balanced it is, the more predictable it will be and the better your chances. Don’t misread the situation though; your chances will never be any worse than they would have been if you hadn’t been selective.

The third principle tells us that. Remembering this, you should only read the tables in section 19.3 if you subscribe to the three principles and you think selectivity is for you. If you don’t recognize the code references, clause numbers or abbreviations then you need to start again at the beginning of this book.

19.3 Exam selectivity

For the wise

Question Subject: open book
1 RT density
2 RT backscatter symbol
3 Condensate corrosion
4 Hydrotest pressure
5 HTHA
6 RT joint type
7 Reformer failure
8 WFMT cleaning
9 CD welding
10 Wall thickness calculation
11 RT slag acceptance
12 Re-rating Fig. 8.1
13 Plate offset
14 NPS 2 nozzle to shell
15 PRV set pressure
16 MDMT
17 RT records
18 Vessel head calculation
19 Remaining life
20 Repair authorization
21 Dry MT temperatures
22 Corrosion averaging
23 PRV removal
24 P-number
25 Heat treatment
26 Average thickness
27 Charpy specimen length
28 Essential variables
29 CMLs
30 Temporary repair dimensions
31 Corrosion rate
32 pH values
33 Defects at weld toes
34 PWHT
35 Weld processes
36 API 579
37 Repair welding
38 Missing documents
39 CD welding (again)
40 Charpy values table
41 Pneumatic tests
42 Vessel linings
43 Corrosion buttons
44 Elliptical head calculation
45 RT step wedge
46 Sulphidation
47 CD welding in lieu of PWHT
48 Static head
49 Concrete foundations
50 Cooling water corrosion
For the hopeful*
Question Subject: open book
1 Factual questions from API 510 sections 1–4 that fit my experience
2
3
4
5 Hard engineering logic questions from API 510 sections 5 and 6
6
7
8 Experience-based questions from API 510 section 7
9
10
11 API 510 section 8
12
13
14
15 ASME VIII head and shell calculations (easy if you can use a calculator)
16
17
18
19 Pressure testing questions (may need to consult the parrot)
20
21
22
23 Easily found points from API 572 that are obvious to anyone in this inspection business
24
25
26
27
28 API 571 DM questions . . . I’ll have a guess at those . . .
29
30
31
32
33
34 NDE questions from ASME V

… .. No problem with my previous experience. I used to be an NDE technician, you know

35
36
37
38
39
40
41
42
43
44 Easily found points from API 577 that I agree with
45
46
47 ASME IX exercise (can be quite tricky . . . hope they’re not too hard)
48
49
50

* Incorrect

API 510 Chapter 17

API 510 Chapter 17 -Thirty Open-Book Sample Questions

Try these questions, using all of the codes specified in the API 510 exam ‘effectivity list’. There is little point in guessing the answers – the objective is to see where the answers come from in the codes, thereby increasing your familiarity with the content.

1.

Question 1
A vessel is constructed to a pre-1999 version of the ASME
construction code. Can it be re-rated to the 1999 version?

 
 
 
 

2.

Question 2
The API philosophy is that temporary repairs should be replaced with permanent repairs

 
 
 
 

3.

Question 3
A procedure is qualified using base material with an S-number.
Which of the following statements is true?

 
 
 
 

4.

Question 4
Which of the following NDE methods would be unlikely to find an edge-breaking lamination in a weld joint

 
 
 
 

5.

Question 5
The inspection interval for all PRVs is determined by:

 
 
 
 

6.

Question 6
Who decides the corrosion rate that best reflects current process conditions

 
 
 
 

7.

Question 7
Providing certain conditions are met, a vessel may be re-rated to:

 
 
 
 

8.

Question 8
Thickness data for a pressure vessel are provided as follows:
Minimum (calculated) thickness = 0.125 in
Current measured thickness = 0.25 in
Measured thickness 4 years ago = 0.50 in
What are the remaining life and the inspection period of the vessel?

 

 
 
 
 

9.

Question 9
Weld repairs to existing stainless steel overlay or clad areas
should consider:

 
 
 
 

10.

Question 10
A pressure vessel has the following data:
. Nameplate stamping RT-2
. MAWP = 280 psig at 690 °F
. S = 13 350 psi
. Actual shell thickness = 0.475 in
. ID = 78.5 in
. Welded joints are all type 1
What is the minimum safe shell thickness to support the rated MAWP of 280 psi?

 
 
 
 

11.

Question 11
For vessels susceptible to brittle fracture, what additional tests should the inspector specifically consider after repair welding is completed?

 
 
 
 

12.

Question 12
A vessel has the following data:
. Elliptical heads joined to the shell by type 1 joints (Cat B) with full RT
. Head ID = 52 in
. Thickness at the knuckle (corroded) = 0.28 in
. S = 13 800 psi
What is the safe MAWP of this head (ignoring any static pressure consideration)?

 
 
 
 

13.

Question 13
For a vessel that has no nameplate, the inspector should specify that a new nameplate is fitted showing:

 
 
 
 

14.

Question 14
RBI assessment should be thoroughly documented in accordance with:

 
 
 
 

15.

Question 15
In API 510, sulphidation is classed as a DM resulting in:

 
 
 
 

16.

Question 16
Which of these is not a material verification (PMI) technique that can be used on-site?

 
 
 
 

17.

Question 17
Plain carbon and other ferritic steels may be in danger of brittle fracture at:

 
 
 
 

18.

Question 18
A vessel constructed of material with a thickness of 0.50 in and UTS of 75 000 psi is to be weld-repaired using weld consumables with UTS of 60 000 psi. If the depth of the weld repair is 0.2 in, what is the total required thickness of the weld deposit?

 
 
 
 

19.

Question 19
A vessel is made from a carbon steel plate (UCS-66 curve A) with a design stress of 17 500 psi. It operates at very low material stress of 100 psi and is made of 1 in the plate that has been spot radiographed. What is the minimum design metal temperature for the material to not require impact testing?

 
 
 
 

20.

Question 20
It is required to investigate whether a scheduled internal inspection on a multizone vessel (with varying corrosion rates)can be substituted by an on-stream inspection. The inspector should:

 
 
 
 

21.

Question 21
If there is a conflict between the ASME codes and API 510 then:

 
 
 
 

22.

Question 22
A nozzle is fitted abutting (i.e. set-on) the vessel wall. What is an acceptable method of attaching it?

 
 
 
 

23.

Question 23
An engineer has passed the NBBPVI inspection examination. Under what conditions can the inspector be awarded an API 510 authorized pressure vessel inspector certificate?

 
 
 
 

24.

Question 24
A vessel has an inside diameter of 30 inches. What is the maximum allowed averaging length for calculating corroded wall thickness?

 
 
 
 

25.

Question 25
What are HIC cracks likely to look like?

 
 
 
 

26.

Question 26
Which of the following is a commonly accepted advantage of the GMAW process?

 
 
 
 

27.

Question 27
How often should an external inspection be performed on an above-ground vessel?

 
 
 
 

28.

Question 28
Which of these vessels in which internal inspection is physically possible, but are in severe corrosive service, may not use an onstream inspection as a substitute for an internal inspection?

 
 
 
 

29.

Question 29
For a vessel that has no nameplate or design/construction information, a pressure test should be performed:

 
 
 
 

30.

Question 30
CMLs should be distributed:

 
 
 
 

Click Here To Read Next API 570 Exam Chapter 19 – The Final Word on Exam Questions 

API 510 Chapter 16

API 510 Chapter 16- The NDE Requirements of ASME V

16.1 Introduction

This chapter is to familiarize you with the specific NDE requirements contained in ASME V. ASME VIII references ASME V as the supporting code but only articles 1, 2, 6, 7, 9 and 23 are required for use in the API 510 examination. These articles of ASME V provide the main detail of the NDE techniques that are referred to in many of the API codes. Note that it is only the body of the articles that are included in the API examinations; the additional (mandatory and non-mandatory) appendices that some of the articles have are not examinable. We will now look at each of the articles 1, 2, 6, 7, 9 and 23 in turn.

16.2 ASME V article 1: general requirements

Article 1 does little more than set the general scene for the other articles that follow. It covers the general requirement for documentation procedures, equipment calibration and records, etc., but doesn’t go into technique-specific detail. Note how the subsections are annotated with T-numbers (as opposed to I-numbers used for the appendices).

Manufacturer versus repairer One thing that you may find confusing in these articles is the continued reference to The Manufacturer. Remember that ASME V is really a code intended for new manufacture. We are using it in its API 570 context, i.e. when it is used to cover repairs. In this context, you can think of The Manufacturer as The Repairer.

Table A-110: imperfections and types of NDE method This table lists imperfections in materials, components and welds and the suggested NDE methods capable of detecting them. Note how it uses the terminology imperfection some of the other codes would refer to these as discontinuities or indications (yes, it is confusing). Note that table A-110 is divided into three types of imperfection:

  • Service-induced imperfections
  • Welding imperfections
  • Product form

We are mostly concerned with the service-induced imperfections and welding imperfections because our NDE techniques are to be used with API 570, which deals with in-service inspections and welding repairs.

The NDE methods in table A-110 are divided into those that are capable of finding imperfections that are:

  • Open to the surface only
  • Open to the surface or slightly subsurface
  • Located anywhere through the thickness examined

Note how article 1 provides very basic background information only. The main requirements appear in the other articles, so API examination questions on the actual content of article 1 are generally fairly rare. If they do appear they will probably be closed book, with a very general theme.

16.3 ASME V article 2: radiographic examination

ASME V article 2 covers some of the specifics of radiographic testing techniques. Note that it does not cover anything to do with the extent of RT on pipework, i.e. how many radiographs to take or where to do them (we have seen previously that these are covered in ASME B31.3).

Most of article 2 is actually taken up by details of image quality indicators (IQIs) or penetrameters, and parameters such as radiographic density, geometric unsharpness and similar detailed matters. While this is all fairly specialized, it is fair to say that the subject matter lends itself more to openbook exam questions rather than closed-book ‘memory’ types of questions.

T-210: scope This explains that article 2 is used in conjunction with the general requirements of article 1 for the examination of materials including castings and welds.

Note that there are seven mandatory appendices detailing the requirements for other product-specific, techniquespecific and application-specific procedures. Apart from appendix V, which is a glossary of terms, do not spend time studying these appendices. Just look at the titles and be aware they exist. The same applies to the three non mandatory appendices.

T-224: radiograph identification Radiographs have to contain unique traceable permanent identification, along with the identity of the manufacturer and date of radiograph. The information need not be an image that actually appears on the radiograph itself (i.e. it could be from an indelible marker pen) but usually is.

T-276: IQI (image quality indicator) selection T-276.1: material IQIs have to be selected from either the same alloy material group or an alloy material group or grade with less radiation absorption than the material being radiographed.

Remember that the IQI gives an indication of how ‘sensitive’ a radiograph is. The idea is that the smallest wire visible will equate to the smallest imperfection size that will be visible on the radiograph.

T-276.2: size of IQI to be used (see Fig. 16.1) Table T-276 specifies IQI selection for various material thickness ranges. It gives the designated hole size (for hole type IQIs) and the essential wire (for wire type IQIs) when the IQI is placed on either the source side or film side of the weld. Note that the situation differs slightly depending on whether the weld has reinforcement (i.e. a weld cap) or not.

Figure 16.1 IQI selection
Figure 16.1 IQI selection

T-277: use of IQIs to monitor radiographic examination

T-277.1: placement of IQIs For the best results, IQIs are placed on the source side (i.e. nearest the radiographic source) of the part being examined. If inaccessibility prevents hand-placing the IQI on the source side, it can be placed on the film side in contact with the part being examined. If this is done, a lead letter ‘F’ must be placed adjacent to or on the IQI to show it is on the film side. This will show up on the film.

IQI location for welds. Hole type IQIs can be placed adjacent to or on the weld. Wire IQIs are placed on the weld so that the length of the wires is perpendicular to the length of the weld. The identification number(s) and, when used, the lead letter ‘F’ must not be in the area of interest, except where the geometric configuration of the component makes it impractical.

T-277.2: number of IQIs to be used At least one IQI image must appear on each radiograph (except in some special cases). If the radiographic density requirements are met by using more than one IQI, one must be placed in the lightest area and the other in the darkest area of interest. The idea of this is that the intervening areas are then considered as having acceptable density (a sort of interpolation).

T-280: evaluation of radiographs (Fig. 16.2) This section gives some quite detailed ‘quality’ requirements designed to make sure that the radiographs are readable and interpreted correctly.

T-282: radiographic density These are specific requirements that are based on very well established requirements used throughout the NDE industry. It gives numerical values of density (a specific measured parameter) that have to be met for a film to be considered acceptable.

Figure 16.2 Evaluation of radiographs
Figure 16.2 Evaluation of radiographs

T-282.1: density limitations This specifies acceptable density limits as follows:

  • Single film with X-ray source: density = 1.8 to 4.0
  • Single film with gamma-ray source: density = 2.0 to 4.0
  • Multiple films: density = 0.3 to 4.0

A tolerance of 0.05 in density is allowed for variations between densitometer readings.

  • T-283: IQI sensitivity
  • T-283.1: required sensitivity

In order for a radiograph to be deemed ‘sensitive enough’ to show the defects of a required size, the following things must be visible when viewing the film:

  • For a hole type IQI: the designated hole IQI image and the 2T hole
  • For a wire type IQI: the designated wire .
  • IQI identifying numbers and letters
Figure 16.3 Backscatter gives an unclear image
Figure 16.3 Backscatter gives an unclear image

T-284: excessive backscatter Backscatter is a term given to the effect of scattering of the X or gamma rays, leading to an unclear image.

If a light image of the lead symbol ‘B’ appears on a darker background on the radiograph, protection from backscatter is insufficient and the radiograph is unacceptable. A dark image of ‘B’ on a lighter background is acceptable (Fig. 16.3).

T-285: geometric unsharpness limitations Geometric unsharpness is a numerical value related to the ‘fuzziness’ of a radiographic image, i.e. an indistinct ‘penumbra’ area around the outside of the image. It is represented by a parameter Ug (unsharpness due to geometry) calculated from the specimen-to-film distance, focal spot size, etc.

Article 2 section T-285 specifies that geometric unsharpness (Ug) of a radiograph shall not exceed the following:

Material                                           Ug

thickness, in (mm)                         Maximum, in (mm)

Under 2 (50.8)                               0.020 (0.51)

2  through 3 (50.8–76.2)                0.030 (0.76)

Over  3  through  4  (76.2–101.6)  0.040  (1.02)

Greater  than 4 (101.6)                   0.070 (1.78)

In all cases, material thickness is defined as the thickness on which the IQI is chosen.

16.4 ASME V article 6: penetrant testing (PT)

T-620: general This article of ASME V explains the principle of penetrant testing (PT). We have already covered much of this in API 577, but ASME V article 6 adds some more formal detail.

T-642: surface preparation before doing PT Surfaces can be in the as-welded, as-rolled, as-cast or as forged condition and may be prepared by grinding, machining or other methods as necessary to prevent surface irregularities masking indications. The area of interest, and adjacent surfaces within 1 inch (25 mm), need to be prepared and degreased so that indications open to the surface are not obscured.

T-651: the PT techniques themselves

Article 6 recognizes three penetrant processes:

  • Water washable
  • Post-emulsifying (not water based but will wash off with water)
  • Solvent removable

The three processes are used in combination with the two penetrant types (visible or fluorescent), resulting in a total of six liquid penetrant techniques.

T-652: PT techniques for standard temperatures For a standard PT technique, the temperature of the penetrant and the surface of the part to be processed must be between 50 8F (10 °C) and 125 °F (52 °C) throughout the examination period. Local heating or cooling is permitted to maintain this temperature range.

T-670: the PT examination technique (see Fig. 16.4)

Figure 16.4 PT examination technique
Figure 16.4 PT examination technique

T-671: penetrant application

Penetrant may be applied by any suitable means, such as dipping, brushing or spraying. If the penetrant is applied by spraying using compressed-air type apparatus, filters have to be placed on the upstream side near the air inlet to stop contamination of the penetrant by oil, water, dirt or sediment that may have collected in the lines.

T-672: penetration time

Penetration time is critical. The minimum penetration time must be as required in table T-672 or as qualified by demonstration for specific applications.

Note: While it is always a good idea to follow the manufacturers’ instructions regarding use and dwell times for their penetrant materials, table T-672 lays down minimum dwell times for the penetrant and developer. These are the minimum values that would form the basis of any exam questions based on ASME V.

T-676: interpretation of PT results

T-676.1: final interpretation Final interpretation of the PT results has to be made within 10 to 60 minutes after the developer has dried. If bleed-out does not alter the examination results, longer periods are permitted. If the surface to be examined is too large to complete the examination within the prescribed or established time, the examination should be performed in increments.

This is simply saying: inspect within 10–60 minutes. A longer time can be used if you expect very fine imperfections. Very large surfaces can be split into sections.

T-676.2: characterizing indication(s) Deciding (called characterizing in ASME-speak) the types of discontinuities can be difficult if the penetrant diffuses excessively into the developer. If this condition occurs, close observation of the formation of indications during application of the developer may assist in characterizing and determining the extent of the indications; i.e. the shape of deep indications can be masked by heavy leaching out of the penetrant, so it is advisable to start the examination of the part as soon as the developer is applied.

T-676.4: fluorescent penetrants With fluorescent penetrants, the process is essentially the same as for colour contrast, but the examination is performed using an ultraviolet light, sometimes called black light. This is performed as follows:

(a) It is performed in a darkened area.

(b) The examiner must be in the darkened area for at least 5 minutes prior to performing the examination to enable his or her eyes to adapt to dark viewing. He or she must not wear photosensitive glasses or lenses.

(c) Warm up the black light for a minimum of 5 min prior to use and measure the intensity of the ultraviolet light emitted. Check that the filters and reflectors are clean and undamaged.

(d) Measure the black light intensity with a black lightmeter. A minimum of 1000 μW/cm2 on the surface of the part being examined is required. The black light intensity must be re-verified at least once every 8 hours, whenever the workstation is changed or whenever the bulb is changed.

T-680: evaluation of PT indications Indications are evaluated using the relevant code acceptance criteria (e.g. B31.3 for pipework). Remember that ASME V does not give acceptance criteria. Be aware that false indications may be caused by localized surface irregularities. Broad areas of fluorescence or pigmentation can mask defects and must be cleaned and re-examined.

Now try these familiarization questions on ASME V articles 1, 2 and 6.

16.5 ASME V articles 1, 2 and 6: familiarization questions

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16.6 ASME V article 7: magnetic testing (MT)

Similar to the previous article 6 covering penetrant testing, this article 7 of ASME V explains the technical principle of magnetic testing (MT). As with PT, we have already covered much of this in API 577, but article 7 adds more formal detail. Remember again that it is not component specific; it deals with the MT techniques themselves, not the extent of MT you have to do on a pressure vessel.

T-720: general MT methods are used to detect cracks and other discontinuities on or near the surfaces of ferromagnetic materials. It involves magnetizing an area to be examined, then applying ferromagnetic particles to the surface, where they form patterns where the cracks and other discontinuities cause distortions in the normal magnetic field.

Maximum sensitivity is achieved when linear discontinuities are orientated perpendicular to the lines of magnetic flux. For optimum effectiveness in detecting all types of discontinuities, each area should therefore be examined at least twice, with the lines of flux during one examination approximately perpendicular to the lines of flux during the other; i.e. you need two field directions to do the test properly.

T-750: the MT techniques (see Fig. 16.5)

One or more of the following five magnetization techniques can be used:

(a) Prod technique

(b) Longitudinal magnetization technique

(c) Circular magnetization technique

(d) Yoke technique

(e) Multidirectional magnetization technique

Figure 16.5 MT examination technique
Figure 16.5 MT examination technique

The API examination will be based on the prod or yoke techniques (i.e. (a) or (d) above), so these are the only ones we will consider. The others can be ignored for exam purposes.

T-752: the MT prod technique

T-752.1: the magnetizing procedure Magnetization is accomplished by pressing portable prod type electrical contacts against the surface in the area to be examined. To avoid arcing, a remote control switch, which may be built into the prod handles, must be provided to allow the current to be turned on after the prods have been properly positioned.

T-752.3: prod spacing Prod spacing must not exceed 8 in (203 mm). Shorter spacing may be used to accommodate the geometric limitations of the area being examined or to increase the sensitivity, but prod spacings of less than 3 in (76 mm) are usually not practical due to ‘banding’ of the magnetic particles around the prods. The prod tips must be kept clean and dressed (to give good contact).

T-755: the MT yoke technique This method must only be used (either with AC or DC electromagnetic yokes or permanent magnet yokes) to detect discontinuities that are surface breaking on the component.

T-764.1: magnetic field strength When doing an MT test, the applied magnetic field must have sufficient strength to produce satisfactory indications, but it must not be so strong that it causes the masking of relevant indications by non-relevant accumulations of magnetic particles. Factors that influence the required field strength include:

  • Size, shape and material permeability of the part
  • The magnetization technique
  • Coatings
  • The method of particle application
  • The type and location of discontinuities to be detected

Magnetic field strength can be verified by using one or more of the following three methods:

  • Method 1: T-764.1.1: pie-shaped magnetic particle field indicator
  • Method 2: T-764.1.2: artificial flaw shims
  • Method 3: T-764.1.3 hall effect tangential-field probe

T-773: methods of MT examination (dry and wet) Remember the different types of MT technique. The ferromagnetic particles used as an examination medium can be either wet or dry, and may be either fluorescent or colour contrast:

  • For dry particles the magnetizing current remains on while the examination medium is being applied and excess of the examination medium is removed. Remove the excess particles with a light air stream from a bulb, syringe or air hose (see T-776).
  • For wet particles the magnetizing current will be turned on after applying the particles. Wet particles from aerosol spray cans may be applied before and/or after magnetization. Wet particles can be applied during magnetisation as long as they are not applied with sufficient velocity to dislodge accumulated particles.

T-780: evaluation of defects found during MT As with the other NDE techniques described in ASME V, defects and indications are evaluated using the relevant code acceptance criteria (e.g. ASME B31.3). Be aware that false indications may be caused by localized surface irregularities. Broad areas of particle accumulation can mask relevant indications and must be cleaned and re-examined.

16.7 ASME V article 23: ultrasonic thickness checking

In the ASME V code, this goes by the grand title of Standard Practice for Measuring Thickness by Manual Ultrasonic Pulse-Echo Contact Method: section SE-797.2. This makes it sound much more complicated than it actually is. Strangely, it contains some quite detailed technical requirements comprising approximately seven pages of text and diagrams at a level that would be appropriate to a UT qualification exam. The underlying principles, however, remain fairly straightforward. We will look at these as broadly as we can, with the objective of picking out the major points that may appear as closed-book questions in the API examinations.

The scope of article 23, section SE-797

This technique is for measuring the thickness of any material in which ultrasonic waves will propagate at a constant velocity and from which back reflections can be obtained and resolved. It utilizes the contact pulse echo method at a material temperature not to exceed 200 °F (93 °C). Measurements are made from one side of the object, without requiring access to the rear surface.

The idea is that you measure the velocity of sound in the

Figure 16.6 UT thickness checking
Figure 16.6 UT thickness checking

material and the time taken for the ultrasonic pulse to reach the back wall and return (see Fig. 16.6). Halving the result gives the thickness of the material.

Summary of practice

Material thickness (T), when measured by the pulse-echo ultrasonic method, is a product of the velocity of sound in the material and one half the transit time (round trip) through the material. The simple formula is:

T = Vt/2

where

T =thickness

V =velocity

t=transit time

Thickness-checking equipment

Thickness-measurement instruments are divided into three groups:

Flaw detectors with CRT readouts. These display time/ amplitude information in an A-scan presentation (we saw this method in a previous module). Thickness is measured by reading the distance between the zero-corrected initial pulse and first-returned echo (back reflection), or between multiple- back reflection echoes, on a calibrated base-line of a CRT. The base-line of the CRT should be adjusted to read the desired thickness increments.

Flaw detectors with CRT and direct thickness readout. These are a combination pulse ultrasound flaw detection instrument with a CRT and additional circuitry that provides digital thickness information. The material thickness can be electronically measured and presented on a digital readout. The CRT provides a check on the validity of the electronic measurement by revealing measurement variables, such as internal discontinuities, or echo-strength variations, which might result in inaccurate readings.

Direct thickness readout meters. Thickness readout instruments are modified versions of the pulse-echo instrument. The elapsed time between the initial pulse and the first echo or between multiple echoes is converted into a meter or digital readout. The instruments are designed for measurement and direct numerical readout of specific ranges of thickness and materials.

Standardization blocks Article 23 goes into great detail about different types of ‘search units’. Much of this is too complicated to warrant too much attention. Note the following important points.

Section 7.2.2.1: calibration (or standardization) blocks Two ‘calibration’ blocks should be used: one approximately the maximum thickness that the thickness meter will be measuring and the other the minimum thickness.

Thicknesses of materials at high temperatures up to about 540 °C (1000 °F) can be measured with specially designed instruments with high-temperature compensation. A rule of thumb is as follows:

A thickness meter reads 1 % too high for every 55 °C (100 °F) above the temperature at which it was calibrated. This correction is an average one for many types of steel. Other corrections would have to be determined empirically for other materials.

An example. If a thickness meter was calibrated on a piece of similar material at 20 °C (68 °F), and if the reading was obtained with a surface temperature of 460 °C (860 °F), the apparent reading should be reduced by 8 %.

Now try these familiarization questions covering ASME V articles 7 and 23 (article 9 questions are too easy).

16.8 ASME V articles 7 and 23 familiarization questions

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API 510 Chapter 15

API 510 Chapter 15 – The NDE Requirements of API 510 and API 577

15.1 NDE Requirements of API 510 and API 577 In many ways, the API 510 Body of Knowledge contains a patchwork quilt of NDE requirements. Figure 15.1 shows the situation; ASME V, VIII and IX all contain NDE requirements related to their own new construction focus while API 510, 577 and 572 supplement this with their own requirements related to in-service inspection, and then repair. API 510, remember, retains its position as the ‘override’ code – taking priority over the others wherever conflict exists (and there are a few such areas).

Other sections of this book cover the requirements of ASME V, VIII and IX in some detail. These are by far the longest sections, as you would expect, as they come from a fully blown construction code. API 577, being a Recommended Practice (RP) document rather than a formal code, takes an almost ‘textbook’ approach. It contains an extremely diverse, and in places quite deep, coverage of metallurgy, welding, NDE and almost everything else – in many areas far too detailed to be included in the API exam.

15.2 API 510 NDE requirements

Surprisingly, API 510 itself does not contain much direct information on NDE at all. What little it does contain is fragmented throughout various chapters of the code in snippets, rather than in a separate chapter. This has three main results: . It is more difficult to find, as it is not contained in one place. . The ‘snippet’ form makes it more suitable for closed-book exam questions.

Figure 15.1 The API 510 patchwork of NDE requirements
Figure 15.1 The API 510 patchwork of NDE requirements

These questions tend to owe more to examination convenience rather than the value of inspection knowledge they contain.

In fairness, API 510 does not pretend to be an NDEorientated code. It is happy to concentrate more on what to do with the results of NDE activities, leaving the description of the technique themselves to other related codes such as ASME V.

15.2.1 Links to API 571 and API 577

API 571, covering damage mechanisms, contains a lot of information on the NDE technique. It relates these to their suitability for finding the results of various damage mechanisms. This document contains a lot of technical opinion, which means that it has to be judgemental on which NDE techniques can and can’t find specific damage mechanisms and defects. You may find, therefore, that you do not actually agree with all of it.

Referring back to API 510, Fig. 15.2 shows some specific sections that contain NDE requirements. Some of these are fact and some are API opinion, but all can contain valid API 510 exam questions. Note how they are all fairly thin on detail, consisting mainly of short statements rather than elaborate technical argument or justifications.

API 510 SECTION SUBJECT API 510’s VIEW
Definition 3.1 What is a defect? A defect is an indication that exceeds the applicable acceptance criteria.
Definition 3.2 So what is an

indication?

An indication is just something found by NDE – it may be a defect or it may not.
4.2.4 Responsibilities of the inspector It is the inspector’s job to make sure that NDE meets API 510 requirements.
4.2.5 Who actually does the NDE? API 510 calls NDE technicians or operatives examiners.
5.1.2 Where are NDE activities specified? In the inspection plan (see 5.1.2(d)).
5.5.3.2 On-stream inspections Non-intrusive (meaning NDE) examinations can be used in some situations to replace vessel internal examination.
5.7.1 Choice of NDE technique This section (a) to (j) contains multiple value-judgements on which NDE technique is best for finding what – a common source of exam questions.
5.7.1.2 Shear wave operator qualification It is the plant owner/user’s job to specify that shear wave ‘examiners’ need adequate qualification.
5.7.2.1 Thickness measurement methods A, B or C scan UT are suitable for numerous measurement activities.
5.7.2.4 NDE inaccuracies NDE techniques all have measurement inaccuracies.
8.1.2.1 Approval of repairs NDE of repairs must be approved by the inspector.
8.1.5.4.4 Repairs to stainless steel overlay Base metal is to be checked by UT to detect post-weld cracking.
8.1.7 NDE of repair welds PT/MT should be performed on weld preparations before welding.
8.1.7.3 NDE of repair welds Repairs require RT (or equivalent) as per the original construction code that was used for the new vessel.
8.1.8 Weld inspection of brittle components NDE is required to find cracks and notches.
8.2.1 Re-rating NDE is an acceptable substitute for pressure testing in proving vessel integrity.
Annex B3.2 Inspector recertification NDE experience may be considered as ‘active engagement as an inspector’.

Figure 15.2 Specific NDE requirements of API 510 9th edition

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API 510 Chapter 14

API 510 Chapter 14- Welding Qualifications and ASME IX

14.1 Module introduction

The purpose of this chapter is to familiarize you with the principles and requirements of welding qualification documentation. These are the Weld Procedure Specification (WPS), Procedure Qualification Record (PQR) and Welder Performance Qualification (WPQ). The secondary purpose is to define the essential, non-essential and supplementary essential variables used in qualifying WPSs.

ASME section IX is a part of the ASME Boiler Pressure Vessel code that contains the rules for qualifying welding procedures and welders. It is also used to qualify welders and procedures for welding to ASME VIII.

14.1.1 Weld procedure documentation: which code to follow?

API 510 (section 8.1.6.2.1) requires that repair organizations must use welders and welding procedures qualified to ASME IX and maintain records of the welding procedures and welder performance qualifications. ASME IX article II states that each Manufacturer and Contractor shall prepare written Welding Procedure Specifications (WPSs) and a Procedure Qualification Record (PQR), as defined in section QW-200.2.

14.2 Formulating the qualification requirements

The actions to be taken by the manufacturer to qualify a WPS and welder are done in the following order (see Fig. 14.1):

Figure 14.1 Formulating the qualification requirements
Figure 14.1 Formulating the qualification requirements

Step 1: qualify the WPS . A preliminary WPS (this is an unsigned and unauthorized document) is prepared specifying the ranges of essential variables, supplementary variables (if required) and nonessential variables required for the welding process to be used. . The required numbers of test coupons are welded and the ranges of essential variables used recorded on the PQR. . Any required non-destructive testing and/or mechanical testing is carried out and the results recorded in the PQR. . If all the above are satisfactory then the WPS is qualified using the documented information on the PQR as proof that the WPS works. The WPS (see Fig. 14.2) is signed and authorized by the manufacturer for use in production. Step 2: qualify the welder. The next step is to qualify the welder by having him weld a test coupon to a qualified WPS. The essential variables used, tests and results are noted and the ranges qualified on a Welder Performance Qualification (WPQ) (see Fig. 14.3). Note that ASME IX does not require the use of preheat or PWHT on the welder test coupon. This is because it is the skill of the welder and his ability to follow a procedure that is being tested. The pre- and PWHT are not required because the mechanical properties of the joint have already been determined during qualification of the WPS.

Figure 14.2a WPS format
Figure 14.2a WPS format
Figure 14.2b WPS format
Figure 14.2b WPS format
Figure 14.3a PQR format
Figure 14.3a PQR format
Figure 14.3b PQR format
Figure 14.3b PQR format

14.2.1 WPSs and PQRs: ASME IX section QW-250

We will now look at the ASME IX code rules covering WPSs and PQRs. The code section splits the variables into three groups:

  • Essential variables
  • Non-essential variables
  • Supplementary variables

These are listed on the WPS for each welding process. ASME IX section QW-250 lists the variables that must be specified on the WPS and PQR for each process. Note how this is a very long section of the code, consisting mainly of tables covering the different welding processes. There are subtle differences between the approaches to each process, but the guiding principles as to what is an essential, non-essential and supplementary variable are much the same.

14.2.2 ASME IX welding documentation formats

The main welding documents specified in ASME IX have examples in non-mandatory appendix B section QW-482. Strangely, these are not included in the API 510 exam code document package but fortunately two of them, the WPS and PQR, are repeated in API 577 (have a look at them in API 577 appendix C). Remember that the actual format of the procedure sheets is not mandatory, as long as the necessary information is included.

The other two that are in ASME IX non-mandatory appendix B (the WPQ and Standard Weld Procedure Specification (SWPS)) are not given in API 577 and are therefore a bit peripheral to the API 510 exam syllabus.

14.3 Welding documentation reviews: the exam questions

The main thrust of the API 510 ASME IX questions is based on the requirement to review a WPS and its qualifying PQR, so these are the documents that you must become familiar with. The review will be subject to the following limitations (to make it simpler for you):

  • The WPS and its supporting PQR will contain only one welding process.
  • The welding process will be SMAW, GTAW, GMAW or SAW and will have only one filler metal.
  • The base material P group number will be either P1, P3, P4, P5 or P8.

Base materials are assigned P-numbers in ASME IX to reduce the amount of procedure qualifications required. The P-number is based on material characteristics like weldability and mechanical properties. S-numbers are the same idea as Pnumbers but deal with piping materials from ASME B31.3.

14.3.1 WPS/PQR review questions in the exam

The API 510 certification exam requires candidates to review a WPS and its supporting PQR. The format of these will be based on the sample documents contained in annex B of ASME IX. Remember that this annex B is not contained in your code document package; instead, you have to look at the formats in API 577 appendix B, where they are shown (they are exactly the same).

The WPS/PQR documents are designed to cover the parameters/variables requirements of the SMAW, GTAW, GMAW and SAW welding processes. The open-book questions on these documents in the API exam, however, only contain one of those welding processes. This means that there will be areas on the WPS and PQR documents that will be left unaddressed, depending on what process is used. For example, if GTAW welding is not specified then the details of tungsten electrode size and type will not be required on the WPS/PQR.

In the exam questions, you will need to understand the variables to enable you to determine if they have been correctly addressed in the WPS and PQR for any given process

Figure 14.4 The ASME IX numbering system
Figure 14.4 The ASME IX numbering system

14.3.2 Code cross-references

One area of ASME IX that some people find confusing is the numbering and cross-referencing of paragraphs that takes place throughout the code. Figure 14.4 explains how the ASME IX numbering system works.

14.4 ASME IX article I

Article 1 contains less technical ‘meat’ than some of the following articles (particularly articles II and IV). It is more a collection of general statements than a schedule of firm technical requirements. What it does do, however, is cross reference a lot of other clauses (particularly in article IV), which is where the more detailed technical requirements are contained.

From the API exam viewpoint, most of the questions that can be asked about article I are:

  • More suitable to closed-book questions than open-book ones .
  • Fairly general and ‘commonsense’ in nature

Don’t ignore the content of article I. Read the following summaries through carefully but treat article I more as a lead-in to the other articles, rather than an end in itself.

Section QW-100.1

This section tells you five things, all of which you have met before. There should be nothing new to you here. They are:

  • A Weld Procedure Specification (WPS) has to be qualified (by a PQR) by the manufacturer or contractor to determine that a weldment meets its required mechanical properties.
  • The WPS specifies the conditions under which welding is performed and these are called welding ‘variables’.
  • The WPS must address the essential and non-essential variables for each welding process used in production.
  • The WPS must address the supplementary essential variables if notch toughness testing is required by other code sections.
  • A Procedure Qualification Record (PQR) will document the welding history of the WPS test coupon and record the results of any testing required.

Section QW-100.2

A welder qualification (i.e. the WPQ) is to determine a welder’s ability to deposit sound weld metal or a welding operator’s mechanical ability to operate machine welding equipment.

14.5 Section QW-140 types and purposes of tests and examinations

Section QW-141: mechanical tests

Mechanical tests used in procedure or performance qualification are as follows:

QW-141.1: tension tests (see Fig. 14.5). Tension tests are used to determine the strength of groove weld joints.

QW-141.2: guided-bend tests (see Fig. 14.6). Guided-bend tests are used to determine the degree of soundness and ductility of groove-weld joints.

QW-141.3: fillet-weld tests. Fillet weld tests are used to

Figure 14.5 Tension tests
Figure 14.5 Tension tests
Figure 14.6 Guided bend tests
Figure 14.6 Guided bend tests

determine the size, contour and degree of soundness of fillet welds.

QW-141.4: notch-toughness tests. Tests are used to determine the notch toughness of the weldment.

14.6 ASME IX article II Article II

contains hard information about the content of the WPS and PQRs and how they fit together. In common with article I, it cross-references other clauses (particularly in article IV). From the API examination viewpoint there is much more information in here that can form the basis of open-book questions, i.e. about the reviewing of WPS and PQR. ASME IX article II is therefore at the core of the API examination requirements.

Section QW-200: general This gives lists of (fairly straightforward) requirements for the WPS and PQR:

QW-200.1 covers the WPS. It makes fairly general ‘principle’ points that you need to understand (but not remember word-for-word).

QW-200.2 covers the PQR again. It makes fairly general ‘principle’ points that you need to understand (but not remember word-for-word).

QW-200.3: P-numbers. P-numbers are assigned to base metals to reduce the number of welding procedure qualifications required. For steel and steel alloys, group numbers are assigned additionally to P-numbers for the purpose of procedure qualification where notch-toughness requirements are specified.

Now try these familiarization questions, using ASME IX articles I and II to find the answers.

14.7 ASME IX articles I and II familiarization questions

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14.8 ASME IX article III

Remember that WPQs are specific to the welder. While the content of this article is in the API 510 syllabus it is fair to say that it commands less importance than articles II (WPSs and PQRs and their relevant QW-482 and QW-483 format forms) and article IV (welding data).

Section QW-300.1 This article lists the welding processes separately, with the essential variables that apply to welder and welding operator performance qualifications. The welder qualification is limited by the essential variables listed in QW-350, and defined in article IV Welding data, for each welding process. A welder or welding operator may be qualified by radiography of a test coupon or his initial production welding, or by bend tests taken from a test coupon. Look at these tables below and mark them with post-it notes:

  • Table QW-353 gives SMAW essential variables for welder qualification.
  • Table QW-354 gives SAW essential variables for welder qualification.
  • Table QW-355 gives GMAW essential variables for welder qualification.
  • Table QW-356 gives GTAW essential variables for welder qualification.

Section QW-351: variable for welders (general) A welder needs to be requalified whenever a change is made in one or more of the essential variables listed for each welding process. The limits of deposited weld metal thickness for which a welder will be qualified are dependent upon the thickness of the weld deposited with each welding process, exclusive of any weld reinforcement.

In production welds, welders may not deposit a thickness greater than that for which they are qualified.

14.9 ASME IX article IV

Article IV contains core data about the welding variables themselves. Whereas article II summarizes which variables are essential/non-essential/supplementary for the main welding processes, the content of article IV explains what the variables actually are. Note how variables are subdivided into procedure and performance aspects.

Section QW-401: general Each welding variable described in this article is applicable as an essential, supplemental essential or non-essential variable for procedure qualification when referenced in QW-250 for each specific welding process. Note that a change from one welding process to another welding process is an essential variable and requires requalification.

Section QW-401.1: essential variable (procedure) This is defined as a change in a welding condition that will affect the mechanical properties (other than notch toughness) of the weldment (for example, change in P-number, welding process, filler metal, electrode, preheat or post-weld heat treatment, etc.).

Section QW-401.2: essential variable (performance) A change in a welding condition that will affect the ability of a welder to deposit sound weld metal (such as a change in welding process, electrode F-number, deletion of backing, technique, etc.).

Section QW-401.3: supplemental essential variable (procedure) A change in a welding condition that will affect the notchtoughness properties of a weldment (e.g. change in welding process, uphill or downhill vertical welding, heat input, preheat or PWHT, etc.).

Section QW-401.4: non-essential variable (procedure) A change in a welding condition that will not affect the mechanical properties of a weldment (such as joint design, method of back-gouging or cleaning, etc.)

Section QW-401.5 The welding data include the welding variables grouped as follows:

  • QW-402 joints
  • QW-403 base metals
  • QW-404 filler metal
  • QW-405 position
  • QW-406 preheat
  • QW-407 post-weld heat treatment
  • QW-408 gas
  • QW-409 electrical characteristics
  • QW-410 technique

Section QW-420.1: P-numbers P-numbers are groupings of base materials of similar properties and usability. This grouping of materials allows a reduction in the number of PQRs required. Ferrous Pnumber metals are assigned a group number if notch toughness is a consideration.

Section QW-420.2: S-numbers (non-mandatory) S-numbers are similar to P-numbers but are used on materials not included within ASME BPV code material specifications (section II). There is no mandatory requirement that S-numbers have to be used, but they often are. Note these two key points:

  • For WPS a P-number qualifies the same S-number but not vice versa.
  • For WPQ a P-number qualifies the same S-number and vice versa.

Section QW-430: F-numbers The F-number grouping of electrodes and welding rods is based essentially on their usability characteristics. This grouping is made to reduce the number of welding procedure and performance qualifications, where this can logically be done.

Section QW-432.1 Steel and steel alloys utilize F-1 to F-6 and are the most commonly used ones.

Section QW-492: definitions QW-492 contains a list of definitions of the common terms relating to welding and brazing that are used in ASME IX.

Try these ASME IX articles III and IV familiarization questions. You will need to refer to your code to find the answers.

14.10 ASME IX articles III and IV familiarization questions

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14.11 The ASME IX review methodology

One of the major parts of all the API in-service inspection examinations is the topic of weld procedure documentation review. In addition to various ‘closed-book’ questions about welding processes and techniques, the exams always include a group of ‘open-book’ questions centred around the activity of checking a Weld Procedure Specification (WPS) and Procedure Qualification Record (PQR).

Note the two governing principles of API examination questions on this subject: .

  • The PQR and WPS used in exam examples will only contain one welding process and filler material.
  • You need only consider essential and non-essential variables (you can ignore supplementary variables).

The basic review methodology is divided into five steps (see Fig. 14.7). Note the following points to remember as you go through the checklist steps of Fig. 14.7:

  • The welding process is an essential variable and is likely to be SMAW, GTAW, GMAW or SAW.
  • Non-essential variables do not have to be recorded in the PQR (but may be at the manufacturer’s discretion) and must be addressed in the WPS.
  • Information on the PQR will be actual values used whereas the WPS may contain a range (e.g. the base metal actual thickness shown in a PQR may be 1 /2 in, while the base metal thickness range in the WPS may be 3/16 in–1 in). .
  • The process variables listed in tables QW-252 to QW-265
Figure 14.7 The ASME IX WPS/PQR review methodology
Figure 14.7 The ASME IX WPS/PQR review methodology

are referred to as the ‘brief of variables’ and must not be used on their own. You must refer to the full variable requirements referenced in ASME IX article 4 otherwise you will soon find yourself in trouble.

The base material will be either P-1, P-3, P-4, P-5 or P-8 (base materials are assigned P-numbers in ASME IX to reduce the amount of procedure qualifications required).

14.12 ASME IX WPS/PQR review: worked example

The following WPS/PQR is for an SMAW process and contains typical information that would be included in an exam question. Work through the example and then try the questions at the end to see if you have understood the method.

Figures 14.8 and 14.9 show the WPS and PQR for an SMAW process. Typical questions are given, followed by their answer and explanation.

Figure 14.8a SMAW worked example (WPS)
Figure 14.8a SMAW worked example (WPS)
Figure 14.8b SMAW worked example (WPS)
Figure 14.8b SMAW worked example (WPS)
Figure 14.9a SMAW worked example (PQR)
Figure 14.9a SMAW worked example (PQR)
Figure 14.9a SMAW worked example (PQR)
Figure 14.9a SMAW worked example (PQR)

Step 1: variable table

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API 510 Chapter 13

API 510 Chapter 13 – Introduction to Welding/API 577

13.1 Module introduction

The purpose of this chapter is to ensure you can recognize the main welding processes that may be specified by the welding documentation requirements of ASME IX. The API exam will include questions in which you have to assess a Weld Procedure Specification (WPS) and its corresponding Procedure Qualification Record (PQR). As the codes used for API certification are all American you need to get into the habit of using American terminology for the welding processes and the process parameters.

This module will also introduce you to the API RP 577 Welding Inspection and Metallurgy in your code document package. This document has only recently been added to the API examination syllabus. As a Recommended Practice (RP) document, it contains technical descriptions and instruction, rather than truly prescriptive requirements.

13.2 Welding processes

There are four main welding processes that you have to learn about:

  • Shielded metal arc welding (SMAW)
  • Gas tungsten arc welding (GTAW)
  • Gas metal arc welding (GMAW)
  • Submerged arc welding (SAW)

The process(es) that will form the basis of the WPS and PQR questions in the API exam will almost certainly be chosen from these.

The sample WPS and PQR forms given in the non mandatory appendix B of ASME IX (the form layout is not strictly within the API 510 examination syllabus, but we will discuss it later) only contain the information for qualifying these processes.

13.2.1 Shielded metal arc (SMAW)

This is the most commonly used technique. There is a wide choice of electrodes, metal and fluxes, allowing application to different welding conditions. The gas shield is evolved from the flux, preventing oxidation of the molten metal pool (Fig. 13.1). An electric arc is then struck between a coated electrode and the workpiece. SMAW is a manual process as the electrode voltage and travel speed is controlled by the welder. It has a constant current characteristic.

Figure 13.1 The shielded metal arc welding (SMAW) process
Figure 13.1 The shielded metal arc welding (SMAW) process

13.2.2 Metal inert gas (GMAW)

In this process, electrode metal is fused directly into the molten pool. The electrode is therefore consumed, being fed from a motorized reel down the centre of the welding torch (Fig. 13.2). GMAW is know as a semi-automatic process as the welding electrode voltage is controlled by the machine.

Tungsten inert gas (GTAW)

This uses a similar inert gas shield to GMAW but the tungsten electrode is not consumed. Filler metal is provided from a separate rod fed automatically into the molten pool (Fig. 13.3). GTAW is another manual process as the welding electrode voltage and travel speed are controlled by the welder.

Submerged arc welding (SAW)

In SAW, instead of using shielding gas, the arc and weld zone are completely submerged under a blanket of granulated flux (Fig. 13.4). A continuous wire electrode is fed into the weld. This is a common process for welding structural carbon or carbon–manganese steelwork. It is usually automatic with

Figure 13.2 The gas metal arc welding (GMAW) process
Figure 13.2 The gas metal arc welding (GMAW) process

Introduction to Welding/API 577

Figure 13.3 The gas tungsten arc welding (GTAW) process
Figure 13.3 The gas tungsten arc welding (GTAW) process

the welding head being mounted on a traversing machine. Long continuous welds are possible with this technique.

Flux-cored arc welding (FCAW)

FCAW is similar to the GMAW process, but uses a continuous hollow electrode filled with flux, which produces the shielding gas (Fig. 13.5). The advantage of the technique is that it can be used for outdoor welding, as the gas shield is less susceptible to draughts.

13.3 Welding consumables

An important area of the main welding processes is that of weld consumables. We can break these down into the following three main areas:

  • Filler (wires, rods, flux-coated electrodes)
  • Flux (granular fluxes)
  • Gas (shielding, trailing or backing)

There are always questions in the API examination about weld consumables.

Figures 13.6 to 13.11 show basic information about the main welding processes and their consumables.

Figure 13.4 The submerged arc welding (SAW) process
Figure 13.4 The submerged arc welding (SAW) process

Introduction to Welding/API 577

Figure 13.5 The flux cored arc welding (FCAW) process
Figure 13.5 The flux cored arc welding (FCAW) process

 

Figure 13.6 Welding consumables
Figure 13.6 Welding consumables

 

Figure 13.7 SMAW consumables
Figure 13.7 SMAW consumables

 

Figure 13.8 SMAW consumables identification
Figure 13.8 SMAW consumables identification

 

Figure 13.10 GMAW consumables
Figure 13.10 GMAW consumables

 

Figure 13.11 SAW consumables
Figure 13.11 SAW consumables

Now try these two sets of familiarization questions about the welding processes and their consumables.

13.4 Welding process familiarization questions

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API 510 Chapter 13 – Introduction to Welding/API 577

13.1 Module introduction

The purpose of this chapter is to ensure you can recognize the main welding processes that may be specified by the welding documentation requirements of ASME IX. The API exam will include questions in which you have to assess a Weld Procedure Specification (WPS) and its corresponding Procedure Qualification Record (PQR). As the codes used for API certification are all American you need to get into the habit of using American terminology for the welding processes and the process parameters.

This module will also introduce you to the API RP 577 Welding Inspection and Metallurgy in your code document package. This document has only recently been added to the API examination syllabus. As a Recommended Practice (RP) document, it contains technical descriptions and instruction, rather than truly prescriptive requirements.

13.2 Welding processes

There are four main welding processes that you have to learn about:

  • Shielded metal arc welding (SMAW)
  • Gas tungsten arc welding (GTAW)
  • Gas metal arc welding (GMAW)
  • Submerged arc welding (SAW)

The process(es) that will form the basis of the WPS and PQR questions in the API exam will almost certainly be chosen from these.

The sample WPS and PQR forms given in the non mandatory appendix B of ASME IX (the form layout is not strictly within the API 510 examination syllabus, but we will discuss it later) only contain the information for qualifying these processes.

13.2.1 Shielded metal arc (SMAW)

This is the most commonly used technique. There is a wide choice of electrodes, metal and fluxes, allowing application to different welding conditions. The gas shield is evolved from the flux, preventing oxidation of the molten metal pool (Fig. 13.1). An electric arc is then struck between a coated electrode and the workpiece. SMAW is a manual process as the electrode voltage and travel speed is controlled by the welder. It has a constant current characteristic.

Figure 13.1 The shielded metal arc welding (SMAW) process
Figure 13.1 The shielded metal arc welding (SMAW) process

13.2.2 Metal inert gas (GMAW)

In this process, electrode metal is fused directly into the molten pool. The electrode is therefore consumed, being fed from a motorized reel down the centre of the welding torch (Fig. 13.2). GMAW is know as a semi-automatic process as the welding electrode voltage is controlled by the machine.

Tungsten inert gas (GTAW)

This uses a similar inert gas shield to GMAW but the tungsten electrode is not consumed. Filler metal is provided from a separate rod fed automatically into the molten pool (Fig. 13.3). GTAW is another manual process as the welding electrode voltage and travel speed are controlled by the welder.

Submerged arc welding (SAW)

In SAW, instead of using shielding gas, the arc and weld zone are completely submerged under a blanket of granulated flux (Fig. 13.4). A continuous wire electrode is fed into the weld. This is a common process for welding structural carbon or carbon–manganese steelwork. It is usually automatic with

Figure 13.2 The gas metal arc welding (GMAW) process
Figure 13.2 The gas metal arc welding (GMAW) process

Introduction to Welding/API 577

Figure 13.3 The gas tungsten arc welding (GTAW) process
Figure 13.3 The gas tungsten arc welding (GTAW) process

the welding head being mounted on a traversing machine. Long continuous welds are possible with this technique.

Flux-cored arc welding (FCAW)

FCAW is similar to the GMAW process, but uses a continuous hollow electrode filled with flux, which produces the shielding gas (Fig. 13.5). The advantage of the technique is that it can be used for outdoor welding, as the gas shield is less susceptible to draughts.

13.3 Welding consumables

An important area of the main welding processes is that of weld consumables. We can break these down into the following three main areas:

  • Filler (wires, rods, flux-coated electrodes)
  • Flux (granular fluxes)
  • Gas (shielding, trailing or backing)

There are always questions in the API examination about weld consumables.

Figures 13.6 to 13.11 show basic information about the main welding processes and their consumables.

Figure 13.4 The submerged arc welding (SAW) process
Figure 13.4 The submerged arc welding (SAW) process

Introduction to Welding/API 577

Figure 13.5 The flux cored arc welding (FCAW) process
Figure 13.5 The flux cored arc welding (FCAW) process

 

Figure 13.6 Welding consumables
Figure 13.6 Welding consumables

 

Figure 13.7 SMAW consumables
Figure 13.7 SMAW consumables

 

Figure 13.8 SMAW consumables identification
Figure 13.8 SMAW consumables identification

 

Figure 13.10 GMAW consumables
Figure 13.10 GMAW consumables

 

Figure 13.11 SAW consumables
Figure 13.11 SAW consumables

Now try these two sets of familiarization questions about the welding processes and their consumables.

13.4 Welding process familiarization questions

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API 510 Chapter 12

API 510 Chapter 12 – Impact Testing

12.1 Avoiding brittle fracture In any item of structural or pressure equipment there is a need to avoid the occurrence of brittle fracture. As we saw in API 571, brittle fracture is a catastrophic failure mechanism caused by the combination of low temperature and a material that has a low resistance to crack propagation at these temperatures. Under these conditions a material is described as having low toughness (or impact strength) – i.e. it is brittle. Impact strength is measured using a Charpy or Izod test in which a machined specimen is impacted by a swinging hammer. Figure 12.1 shows the situation.

Figure 12.1 The Charpy impact toughness test
Figure 12.1 The Charpy impact toughness test

ASME design codes take a simplified pragmatic view of the avoidance of brittle fracture. Their view is that there are two levels to the checks required:

First, there is a simple set of rules to determine if a material (and its design temperatures) actually needs impact testing or whether it can be assumed to be tough enough without being tested.

Second, if it fails the first set of criteria and does need to be tested, what Charpy (Joules) or Izod (ft-lb) results need to be achieved for the material to be considered codecompliant.

Historically, you can expect a couple of questions in the API 510 exam relating to each of these criteria. The first criterion is a little more difficult to understand as there are several parts to it, and the code is not that easy to interpret on a casual reading. The second part is easier and just involves reading figures from tables, once you know where to find them. We will look at this now in UCS-66.

12.2 Impact exemption UCS-66

The main exam questions on this subject come from the tables and charts of UCS-66. Strictly, there are some opportunities for overall impact test exemptions that may apply before UCS-66 is even considered – these are tucked away in a totally separate part of the code: UG-20. Don’t worry too much about these UG-20 requirements. They appear rarely, if at all, as exam questions, because they would divert attention away from UCS-66, which is where the impact strength questions usually come from.

In concept, UCS-66 is straightforward – the steps are as follows (see Fig. 12.2):

Step 1. For a given material determine, from figure UCS-66, whether it is covered by material curve A, B, C or D. Simply read this off the table, being careful to read the notes at the bottom of the table. In particular, notice that

Figure 12.2a1 The UCS-66 steps. Courtesy of ASME (continues on next page)
Figure 12.2a1 The UCS-66 steps. Courtesy of ASME (continues on next page)

 

Figure 12.2a2 The UCS-66 steps. Courtesy of ASME
Figure 12.2a2 The UCS-66 steps. Courtesy of ASME

 

Figure 12.2b The UCS-66 steps. Courtesy of ASME
Figure 12.2b The UCS-66 steps. Courtesy of ASME

curve A provides a default for any relevant materials not listed in curves B, C or D. Note also how a material that has been normalized may be in a different group to the same material that is non-normalized. This is because normalizing affects the grain structure, and hence the brittle fracture properties.

Step 2. Determine the nominal thickness of the material. This is normally given in the exam question.

Step 3. In figure UCS-66 (for US units) or figure UCS-66M (for SI units), check the material thickness on the lower (horizontal) axis. Then read up the graph until you reach

Figure 12.2b The UCS-66 steps. Courtesy of ASME
Figure 12.2b The UCS-66 steps. Courtesy of ASME

the relevant curve A, B, C or D and read off the corresponding temperature on the vertical axis. Figure 12.2 (a) and (b) shows the procedure.

Step 4. Now the important part – the reading you just obtained on the vertical axis is the minimum temperature at which the component can be used (i.e. designed to be used) without requiring impact tests to check its resistance to brittle fracture. This design temperature is referred to as the minimum design metal temperature (MDMT) and is shown on the vessel nameplate. If you are confused by this, just follow these two rules: 

  • If the required MDMT (i.e. the lowest temperature that you want the vessel to operate at) is higher than the temperature on the vertical axis of figure UCS-66, then impact tests are not required (because the material is not brittle at that temperature).
  • Conversely, if the required MDMT is lower than the temperature on the vertical axis of figure UCS-66, then impact tests are required, to see if the material has sufficient toughness at that temperature.

Step 5. Check the figure UCS-66.1 ‘low stress ratio temperature reduction’. A feature of the ASME VIII-I code is that a material is considered less susceptible to brittle facture at a set temperature if the stress on the component is low. Technically, this is probably a disputable point, but the ASME codes have used it successfully for many years. The stress ratio is defined simply as the amount of stress a component is under compared to the allowable stress that the code allows for the material. It varies from 0 to 1.0, i.e. 0 % to 100 %, and in an exam question is normally given.

Figure UCS-66.1 and Fig. 12.2(c) show how the stress ratio reduction is used. This time, enter the graph on the vertical axis at the given stress ratio, move across to the curve and then read off the coincident temperature on the horizontal axis. This figure is the temperature reduction that can be subtracted from the previous temperature location on the vertical axis of figure UCS-66.

Step 6. Check the UCS-68 (c) ‘voluntary heat treatment temperature reduction’. This is the final potential reduction allowed to the MDMT. Clause UCS-68 (c) (a few pages forward in the code) says that if a vessel is given voluntary heat treatment when it is specifically not required by the code (i.e. because the material is too thin or whatever), then a further 30 °F reduction may be applied to the MDMT temperature point identified on the original UCS-66 vertical axis. Note that this is in addition to any reduction available from the low-stress scenario.

Final step – general ‘capping’ conditions. Hidden in the body of the UCS-66 text are a couple of important ‘capping’ requirements. These occasionally arise in the API exam. The most important one is clause UCS-66 (b)(2). This is there to ensure that the allowable reductions to the impact exemption temperatures don’t go too far. Effectively it ‘caps’ the exemption temperature at 55 °F for all materials. Note, however, the two fairly peripheral exceptions to this when the 55 °F cap can be overridden. These are:

  • When the stress ratio is less than or equal to 0.35 (i.e. the shaded area of figure UCS-66.1). This is set out in UCS-66 (b)(3) and reinforces the ASME code view that components under low stress are unlikely to fail by brittle fracture.
  • When the voluntary heat treatment of UCS-68 (c) has been done and the material is group P1.

The exam questions Historically the API 510 exam questions on impact test exemption are pretty simple. They rarely stray outside the boundary of figure UCS-66 itself. The allowable reduction for low stress ratio and voluntary heat treatment are in the exam syllabus, but don’t appear in the exam very often.

Now try these familiarization questions on impact test exemption.

12.3 ASME VIII section UCS-66: impact test exemption familiarization questions

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API 510 Chapter 11

API 510 Chapter 11- ASME VIII and API 510 Heat Treatment

Post-weld heat treatment (PWHT) is included in the API 510 examination syllabus, mainly in relation to vessel repairs. This makes sense as one of the roles of an API 510 inspector is to oversee repairs on behalf of the plant owner/user. Figure 11.1 shows the importance of this. Not all of the technical information relevant to PWHT is actually included in the API 510 document itself – most is contained in two welldefined (but separated) sections of ASME VIII.

This is not the end of the story. API 510 now adds (as it does with a few other topics) some requirements that can override the PWHT requirements of ASME VIII. The logic behind this is that whereas ASME VIII is a workshop-based construction code, under which PWHT can be done in a furnace under workshop conditions, API 510 deals with repairs, many of which will be carried out on site, where such closely controlled conditions are not possible. API 510 therefore provides easier alternatives that can be legitimately used during repairs. We will look at these parts of the content in turn. 

Figure 11.1 Post-weld heat treatment (PWHT)
Figure 11.1 Post-weld heat treatment (PWHT)

11.1 ASME requirements for PWHT Just about all of the main examination questions on PWHT that relate to ASME VIII are taken from either sections UCS-56 or UW-40. They are well separated in the code document but are cross-referenced directly to each other.

11.2 What is in UCS-56?

UCS-56 contains a couple of pages of text surrounding a group of seven or eight tables. Figure 11.2 shows a sample. The main content is in the tables; their purpose is to specify PWHT temperatures and holding times for different thicknesses of material. Each table covers different P-groups of material – because simplistically, the P-group is related to the tendency of a material to suffer post-weld cracking problems.

11.2.1 UCS-56 table notes

Don’t ignore the half-page or so of notes underneath the various tables contained in UCS-56. They include information on either mandatory requirements or overriding exemptions, based mainly on material thickness.

Most exam questions (open book) will simply involve looking up the relevant PWHT time and temperature for a given material thickness in the correct ‘P-group’ table. Strictly, the material thickness to use is that of nominal thickness. This is defined not in UCS-56 but in UW-40 (f) – Fig. 11.2 shows the main points.

11.2.2 The UCS-56 text sections

There are a number of good open-book examination question subjects hidden away in the two pages of UCS-56 text. These relate to:

  • The rate of heating of the PWHT furnace
  • Allowable temperature variations in the furnace
  • Furnace atmosphere
Figure 11.2 A specimen PWHT table UCS-56 and UW-40 nominal thickness
Figure 11.2 A specimen PWHT table UCS-56 and UW-40 nominal thickness

In addition to these clauses UCS-56 (f) and beyond gives six specific requirements relating to PWHT of weld repairs. In brief they are:

  • The need for notification of repairs .
  • Maximum allowable depths of repair weld (38 mm for P1 Grades 1, 2, 3 and 16 mm for P3 Grades 1, 2, 3 materials)
  • Excavation and PT/MT examination prior to repair
  • Additional WPS requirements
  • Pressure test after repair

Be careful not to misunderstand these requirements – ASME VIII is a construction code only, so the repairs it is referring to in UCS-56 (f) are repairs carried out as part of the original manufacturing process, not repairs carried out after in-service corrosion or some other damage mechanism. For in-service repairs ASME VIII requirements are overridden by the less stringent requirements of API 510 section 8, which does not place any limit on repair weld depth and divides repairs into temporary and permanent types.

11.2.3 The UW-40 text section

Whereas UCS-56 covers the times and temperature requirements for PWHT, UW-40 describes the procedures for how to do it. There are eight main options, some more practical than others.

11.3 API 510 PWHT overrides

API considers it a major advantage to be able to override the ASME VIII requirements for PWHT. Remember the logic behind this – API 510 relates to vessels once they are in use where the practicalities of site working probably will not allow manufacturing shop conditions to be reproduced so easily, if at all.

API 510 section 8.1.6.4 says that, in principle, repair welding must follow the requirements of ASME VIII (it means UW-40 and UCS-56) but opens the door to two overriding PWHT alternatives set out in API 510 section 8.1.6.4.2. This subsection has been progressively expanded and elaborated over recent code editions – you can see this in the out-of-balance subdivisions in the code clauses (it goes to a concentration-popping seven levels of subhierarchy, e.g. section 8.1.6.4.2.2.1).

The two methods of PWHT replacement (section 8.1.6.4.2) are:

  • Replacement of PWHT by preheat
  • Replacement of PWHT by controlled deposition (CD) welding methods

These are shown in Figs 11.3 to 11.5. Both work on the principle that the stress-relieving effects of PWHT can be achieved (albeit imperfectly) by providing the heat required in some other way than placing the repair in a furnace.

11.3.1 Replacement of PWHT by preheat

As the name suggests, this simply involves replacing PWHT with preheating the weld joint and then maintaining the temperature during the welding process. The maintained temperature serves to give sufficient grain refinement to reduce the chances of cracking when the weld is finished and allowed to cool down. While this technique provides sufficient grain refinement it is clearly not as good as full PWHT, so it is limited to materials of P1(Grade 1, 2, 3) and P3(Grade 1, 2) designations. These have a low risk of cracking anyway, owing to their low carbon content. P2 Grade 2 steels containing manganese and molybdenum are excluded, as they have a higher potential for cracking.

API exam questions normally centre around the parameters and restrictions of the preheat techniques. These are listed in API 510 section 8.1.6.4.2.2.1, and illustrated in Fig. 11.4.

11.3.2 Controlled deposition (CD) welding

This is sometimes known as temper-bead welding and is described in some detail in API 510 section 8.1.6.4.2.3. The principle is simple enough – when one layer of weld metal is laid down on top of another the heat from the upper one provides some heat treatment (grain refinement) to the weld underneath. A multilayer weld which is built up in this way will therefore be given an amount of grain refinement throughout its depth. The top layer of the final weld pass will not have anything above it to provide it with heat treatment, so the solution is to grind it off. Figure 11.5 shows the idea.

API 510 (section 6 ) overrides ASME VIII PWHT Requirements API 510 Continues the principle of ifentifying alternatives to full PWHT on weld repaira it identifies 2 methods of replacing PWHT, depending on whether impact (Charpy) testing is involved

Figure 11.3 PWHT replacement options
Figure 11.3 PWHT replacement options

treatment, so the solution is to grind it off. Figure 11.5 shows the idea.

The CD technique is considered to be a little better at replacing full PWHT than the preheat only alternative. It is therefore used for materials where the specification requires impact (notch toughness or Charpy) testing as a condition of their use in pressure equipment. The fact that impact tests were required indicates that the material has a tendency towards brittleness so the preheat method would not be good enough.

These two PWHT replacement techniques, preheat and CD welding, have become a mainstay of API codes. They are now mentioned in API 510, 570 and 653 and, we can assume, are commonly used in practice, although more commonly in the USA than elsewhere. PWHT exam questions PWHT replacement questions seem to be well-represented in the API exam question book. Questions on the validity of the two techniques, times, temperatures and heat-soak band dimensions crop up time and time again.

Now try these familiarization questions.

Figure 11.4 PWHT replacement by preheat
Figure 11.4 PWHT replacement by preheat

 

Figure 11.5 Controlled deposition (temper bead) welding
Figure 11.5 Controlled deposition (temper bead) welding

11.4 ASME VIII sections UCS-56 and UW-40: PWHT familiarization questions

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API 510 Chapter 10

API 510 Chapter 10 – ASME VIII Welding and NDE

10.1 Introduction

This chapter is to familiarize you with the general welding approach contained in sections UW of ASME VIII. API 510 is for in-service inspection of vessels and therefore most welding carried out will be repair welds, rather than welds carried out on new systems. API 510 also makes it a mandatory requirement to comply with the welding rules contained in ASME VIII.

Take a quick look at the scope of sections UW-1 through to UW-65 of the code (which are all of the UW sections). Not all the numbers run consecutively; some are missing. Note the following:

  • Section UW is not just about welding; there are design and NDE-related subjects in there as well.
  • Coverage of welding processes really only starts properly at section UW-27. Before that, the content is more about welded joints themselves, rather than the processes used to weld them.

10.2 Sections UW-1 to UW-5: about joint design

You can think of these sections as an introduction to section UW (don’t ask where UW-4 has gone). Fundamentally, they are about joint design rather than welding techniques but you need them for background information. The best way to understand these is not to read them in the order presented in the code. Start with UW-3 (and its UW-3 figure) and then move to UW-2, which explains the restrictions placed on these joint categories by four special categories of vessel service.

10.2.1 UW-3: welded joint categories

The background to these joint categories is that the ASME design codes (unlike some other vessel codes) are built around the idea of a joint efficiency factor denoted by the symbol E. The factor E appears in the internal pressure equations and depends on:

  • The method of welding
  • The amount of NDE carried out on the weld

Various categories of joints are identified, which (as we will see later) are given different joint efficiencies.

ASME VIII pressure vessel welded joints are given a letter designation A, B, C or D depending on their location in the vessel. The designations are described in section UW-3 and illustrated on the page afterwards in figure UW-3. Note how this figure contains all the practical weld joint types that are found in standard types of pressure vessels. The most critical welds are those classified as category A, as these are the ones that require the most NDE. The content of ASME VIII figure UW-3 is shown in Fig 10.1. Note these points about it shown in the annotations:

Cat A includes all longitudinal welds and critical circumferential welds such as hemispherical head to shell welds.

Cat B includes most circumferential welded joints including formed heads (other than hemispherical) to main shells welds.

Cat C includes welded joints connecting:

  • Flanges to nozzles or shell components.
  • One side plate to another in a flat-sided vessel.

Cat D includes welded joints connecting nozzles to shells, heads or flat-sided vessels.

Note one specific point identified in figure UW-3: a Cat B angled butt weld connecting a transition in diameter (i.e. tapered section) to a cylinder is included as a special requirement provided the angle (see figure UW-3) does not

Figure 10.1 ASME VIII weld categories (courtesy ASME)
Figure 10.1 ASME VIII weld categories (courtesy ASME)

exceed 30°. All the requirements of a butt-welded joint are applied to this angle joint.

This figure UW-3 is of limited use on its own. Its purpose is mainly to link with section UW-12: joint efficiencies. This section, with its accompanying table UW-12, allows you to determine the joint efficiency to use for a weld, as long as you know the category of weld (A–D), the weld joint arrangement (single or double groove, etc.) and the extent of NDE that has been carried out. We will see how to use this soon.

10.2.2 UW-2: service restrictions

Stepping back one section, UW-2 gives guidance on which types of pressure vessels/parts have restrictions on what type of weld should be used for each joint category. The four types of vessels referenced are:

(a) Vessels for lethal service (containing a lethal substance)

(b) Low-temperature vessels that require impact testing

(c) Unfired steam boilers

(d) Direct-fired vessels

These are referenced a, b, c, d in the code. Unfortunately, the page containing these is formatted using an impenetrable hierarchy of subheadings, making the explanations some what difficult to follow.

Most of the ‘meat’ in this section resides in the subsection covering the first category of vessel identified: (a) vessels for lethal service. The other three categories are more or less based on this first one, with some selected changes. Look at the requirement for lethal service and highlight the following key points:

  • Butt-welded joints must be fully radiographed.
  • Carbon or low alloy steel vessels need PWHT.
  • Cat A joints need to be type 1(double vee or equivalent) welds (the types are given in table UW-12).
  • Cat B joints can be either type 1 or type 2 (single vee with backing strip)
  • Cat D must be full penetration welds.

There is a lot in this section about Cat C ‘lap joint stub end’ welds. These are an alternative to forged weld-neck flanges and not particularly common (even though there is a large section on them) except (presumably) on ASME VIII vessels for lethal fluid service.

Note how the (b) category, covering low-temperature vessels, has very similar requirements to the lethal service category, one slight difference being that Cat C welds have to be full penetration. The other two types of vessels, (c) unfired steam boilers and (d) direct-fired pressure vessels, are, again, similar, but with a few changes.

Remember the key point again: 

Most of the ‘meat’ in section UW-2 resides in subsection (a) vessels for lethal service. The other three categories are based on this first one, with some selected changes.

10.3 UW-12: joint efficiencies

UW-12 (text and table) are a core part of the welding requirements of ASME VIII. It is set out as shown in Fig. 10.2. Table UW-12 covers all types of gas and arc welding processes and spreads over two pages. Look at this table in your code and the notes 1–7 at the bottom of the second page of the table. These are often used as the subject matter for open-book examination questions in which table UW-12 is involved.

Now look at the body of table UW-12. It contains the following information:

  • The weld type number – these range from types 1 to 8
  • The joint description for each weld type
  • Any limitations associated with a weld type
  • The joint category (Cat A to D as already seen in UW-3)
  • The degree of RT carried out, subdivided into three levels as follows:
  • Column (a) – full radiography
Figure 10.2 The format of ASME VIII table UW-12
Figure 10.2 The format of ASME VIII table UW-12
  • Column (b) – ‘spot’ radiography
  • Column (c) – no radiography

These RT categories have their origin in section UG-116

Figure 10.2 shows where this is heading. Now look in more detail at ASME VIII table UW-12 and note the following key points:

Look how joint efficiency E depends only on the type of joint and the extent of RT examination carried out on it. The three columns a, b and c cover the situation for conditions of full, ‘spot’ and no RT.

The text is divided into six subsections (a to f) describing a variety of individual cases. You can think of this as elaborating on the content of table UW-12. Look through sections d, e and f in the code and note the points indicated below:

Item (d): seamless (forged) sections of vessels This is a special technical case, but a common area for examination questions. Note what the code says:

(d) Seamless vessel sections are considered equivalent to welded vessel sections of the same geometry in which all Cat A welds are type 1. This applies to both head and shell sections.

Although (by definition) seamless shells or heads have no seams, there is still the need to decide a joint efficiency to use in the pressure design calculations. It is best not to think too deeply about this or you might think it doesn’t quite make sense. ASME VIII obviously thinks it does. The E value to use is set out as follows:

  • E = 1.0 when ‘spot’ RT has been done.
  • E = 0.85 when ‘spot’ RT has not been done or when Cat

A/B welds joining seamless sections together are of type 3, 4, 5 or 6.

Item (e): welded pipe or tubing Following the same impeccable logic as for vessels, welded pipe or tubing is also treated in the same manner as seamless, but with the allowable tensile stress taken from the appropriate ‘welded product’ values in the material stress tables. The requirements of UW-12 (d) are applied as before.

10.4 UW-11: RT and UT examinations

Note the following principles of ASME VIII (UW-11).

10.4.1 RT levels

The three levels of RT are:

  • Full RT (100 % of weld length of code identified welds) .
  • Spot’ RT (a sample of weld length – minimum 6 inches)
  • No RT (radiography not required at all)

The simple principle is that critical welds (those with a high risk of failure due to high stresses) will generally require full radiography to determine whether defects are present that could lead to failure. Welds that are less critical or less likely to fail if they contain a defect may not require full RT but will still require ‘spot’ RT. Joints that are not under internal pressure/high loads are less likely to fail and do not require any RT at all.

10.4.2 Minimum specified RT/UT requirements

This is the most important part of UW-11 (see Fig. 10.3). It gives the six situations where full RT is mandatory under UW-11 (a):

1. All butt welds in the shell and heads of vessels containing lethal substances.

2. All butt welds in vessels over 1 1/2 in (38 mm) thick, or exceeding the thicknesses prescribed in table UCS-57 (have a quick look forward to this table). Note the exemption from this: Cat B/C butt welds in nozzles and communicating chambers ≤ NPS 10 or ≤ 1 1/8 in (29 mm) wall thickness do not require RT. This is a GENERAL

Figure 10.3 Important principles of ASME VIII (UW-11)
Figure 10.3 Important principles of ASME VIII (UW-11)

EXEMPTION FOR SMALL NOZZLES. THESE REQUIRE NO RT AT ALL (so effectively escape ‘under the radar’ from the RT requirements of the various categories RT1, RT2, etc.).

3. All butt welds in the shell/heads of unfired steam boilers exceeding 50 psi (345 kPa).

4. This one covers nozzles. Full RT is required for all butt welds in nozzles, etc., attached to vessel sections or heads that require full RT under (1) or (3) above.

UW-11 (b): ‘spot’ RT

This says that you may use ‘spot’ RT (and use a lower joint efficiency E ) instead of full RT on type 1 or 2 welds.

UW-11 (c): ‘no’ RT As a principle, no RT is required when the vessel or vessel part is designed for external pressure only, or when the joint design complies with UW-12 (c). Sections (d) to (f) cover a few additional UT requirements when specialist welding techniques are used (electrogas, electron beam, etc.).

Note this important point, hidden away at the end in (g):

(g) For RT and UT of butt welds, nominal thickness is the thickness of the thinner of the two parts to be joined. This nominal thickness may be needed to determine if RT or UT is required.

10.5 UW-9: design of welded joints

Finally, we will look at UW-9: design of welded joints. This is more a design issue than a welding one, and there is less to this section than first appears. The main content relates to two areas:

  • Taper transitions between welded sections of unequal thickness
  • Stagger’ of longitudinal welds in vessels

Don’t expect to have to consult detailed figures of weld joints in this section. There is only one figure UW-9, showing the requirement for tapers. Look first at this figure and notice the main points in its descriptive text UW-9 (c):

(c) Tapered transitions requires that tapered transitions must have a taper of at least 3:1 between sections if the sections differ by the smaller of:

  • More than 1/4 of the thickness of the thinner section or .
  • 1/8 in (3.2 mm).

Now move to UW-9 (d). This requires that longitudinal joints between courses must be staggered by at least five times the thickness of the thicker plate unless 4 inches (100 mm) of the joints on either side of the circumferential joint is radiographed (probably unlikely). Note the requirement hidden in the body of the text referencing UW-42. It means that if the taper is formed by weld build-up the additional metal must be examined by PT/MT.

The two points above appear very frequently as API 510 exam questions. Now try these familiarization questions.

10.6 ASME VIII section UW-11 familiarization questions (set 1)

Please go to API 510 Chapter 10 to view the test

10.7 Welding requirements of ASME VIII section UW-16

(a) UW-16 minimum requirements for attachment welds at openings

UW-16 deals with the configuration and size of vessel nozzles and attachments welded into vessels. It gives the location and minimum size of attachment welds and must be used in conjunction with the strength calculations required in UW 15. Note that weld strength calculations are not included in the API 510 syllabus. Note also that the terms nozzles, necks, fittings, pads, etc., mean almost the same thing. This is a fairly complex section about a fairly simple subject, and can be a bit tricky. Have a look at figure UW-16 spread over a few pages of ASME VIII. It produces a few open-book exam questions occasionally, but doesn’t seem to be mainstream content.

(b) Symbols

This paragraph defines the symbols used in UW-16 and in figures UW-16.1 and UW-16.2. You will need to recognize these symbols in order to understand figure UW-16.1, the one with the most important content for exam purposes. The main ones are:

  • t = nominal thickness of vessel shell or head .
  • tn = nominal thickness of nozzle wall

te = thickness of reinforcing plate .

tw = dimension of attachment welds (fillet, single-bevel or single-J), measured as shown in figure UW-16.1 .

tmin = the smaller of 3/4 in (19 mm) or the thickness of the thinner of the parts joined by a fillet, single-bevel or single J weld .

tc = not less than the smaller of 1/4 in (6 mm) or 0.7 tmin.

t1 or t2 = not less than the smaller of 1/4 in (6 mm) or 0.7tmin.

Don’t be put off by these definitions, which look a little complicated. If you have difficulty differentiating between tc, t1, t2 and tw, review them in conjunction with figure UW-16.1 itself.

Paragraphs (c) and (d) cover the two main options for connecting nozzles to shells using Cat D welds.

(c) Necks attached by a full penetration weld Paragraph (c) basically tells us that:

  • A set-on nozzle will have full penetration through the nozzle wall.
  • A set-in nozzle will have penetration through the vessel wall.

Examples of each are then given in sketches UW-16 (a) to UW-16 (e).

To ensure complete weld penetration, backing strips or similar must be used when welding from one side without any method of inspecting the internal root surface.

A nozzle requires a hole to be cut in the shell producing a weakened area that may require strengthening. This strengthening can be added in the following ways:

1. By integral reinforcement (also known as self-reinforcement). This consists of using a thicker shell and/or nozzle, forged inserts or weld build-up, which is integral to the shell or nozzle. Figure UW-16.1 sketches (a), (b), (c), (d), (e), (f-1), (f-2), (f-3), (f-4), (g), (x-1), (y-1) and (z-1) show examples.

 

2. By adding separate reinforcement pads. (These are also termed compensation pads). They are welded to the outside and/or inside surface of the shell wall to increase the thickness in the weakened area. Figure UW-16.1 sketches (a-1), (a-2) and (a-3) give examples of compensated nozzles.

Note the different ways of welding the reinforcement pads to the shell:

At the outer edge of the pad by a fillet weld, and either:

  • where it meets a set-on nozzle, by a full penetration butt weld plus a fillet weld with minimum throat dimension tw 5= 0.7tmin or .
  • where it meets a set-in nozzle, by a fillet weld with minimum throat dimension tw = 0.7tmin(figure UW16.1 sketch (h)).

At the outer and inner edge of the pad by a fillet weld if it does not meet the nozzle. The fillet weld will have a minimum throat dimension of 1/2 tmin. See figure UW-16.1 sketch (a-2) for an example of a fillet welded attachment.

Now try these familiarization questions.

10.8 ASME VIII section UW-16 familiarization questions (set 2)

Please go to API 510 Chapter 10 to view the test

10.9 RT requirements of ASME VIII sections UW-51 and UW-52

Remember API 510? We saw some very general requirements for the NDE of repair welds, using the same principles to those for welds carried out on new systems. This made it a mandatory requirement to comply with the welding rules contained in ASME VIII. We have also seen that ASME VIII contains various requirements for RT, spread around several sections of the code. These included the RT ‘marking’ categories of UW-11 (RT1, RT2, etc.) and the joint efficiencies that result from the choice of RT scope, set out in UW-12. This worked on the general principle of ASME VIII of being able to choose the RT category to follow (within limits), as long as you are happy to live with the joint efficiency that results.

We will now look at some further RT requirements of ASME VIII as set out in sections UW-51 and UW-52. As with all parts of the ASME code, you will find the inevitable cross-references to other code sections, but they are not as extensive here as in some other parts of the code. Have a look at Fig. 10.4; this shows a summary of the referenced sections relating to RT.

Before progressing further with UW-51/UW-52 bear in mind the existence of table UCS-57: radiographic examination (see Fig. 10.5). This table is very important as it gives the nominal wall thickness above which it is mandatory to fully RT butt-welded joints. The content of UW-51 and UW-52 must therefore be seen against the background of these mandatory requirements.

Figure 10.4 A summary of ASME VIII RT
Figure 10.4 A summary of ASME VIII RT

10.9.1 UW-51: ‘full’ RT examination of welded joints

UW-51 and UW-52 are complementary sections. UW-51 deals with ‘full RT’ situations and UW-52 deals with those applicable to ‘spot’ RT.

Starting with UW-51 (a), this specifies that radiographed joints have to be examined in accordance with article 2 of section V. These are well defined and covered in the ASME V chapter of this book. There are a few differences that take

Figure 10.5 RT requirements of UCS-57. Courtesy of ASME
Figure 10.5 RT requirements of UCS-57. Courtesy of ASME

precedence over section V but they are mainly procedural (i.e. documentation/record-related). The main thrust of these is as follows:

  • The manufacturer must retain a complete set of radiographs and records for each vessel until the Inspector has signed the Manufacturer’s Data Report
  • The manufacturer must certify that only qualified and certified radiographers and radiographic interpreters are used
  • Radiographs will only be acceptable if the specified IQI hole or wire is visible

UW-51 (b) specifies conditions under which imperfections (‘indications’) are not acceptable and actions are to be taken. Note the following ‘principle’ point about the use of UT instead of RT:

Unacceptable imperfections must be repaired and reradiographed. The Manufacturer can specify UT instead of RT, providing the original defect has been confirmed by UT to the satisfaction of the Authorized Inspector prior to making the repair. For material > 1 in (25 mm) the User must also agree to its use. This UT examination must be noted under remarks on the Manufacturer’s Data Report Form.

Note: Historically, the ASME code has been built on the premise of using RT as the main volumetric NDE method, but in recent years has started to accept UT as a viable alternative. In reality, however, RT still forms the basis of the ASME code’s approach to integrity and it will probably take many years for this to change.

Defect acceptance criteria

ASME VIII, unlike some codes, does provide information on weld defect acceptance criteria. Note how these are slightly different for the ‘full’ and ‘spot’ RT scenarios. For ‘full’ RT, the following imperfections are unacceptable:

  • Cracks, or incomplete fusion or penetration
  • Elongated indications with lengths greater than the following
  • 1/4 in (6 mm) for t up to 3/4 in (19 mm)
  • 1/3t for t from 3 4 in (19 mm to 21 4 in (57 mm)
  • 3/4 in (19 mm) for t over 2 1/4 in (57 mm

where

t = the thickness of the weld excluding reinforcement

For a butt weld joining two members having different thicknesses at the weld, t is the thinner of these two thicknesses. If a full penetration weld includes a fillet weld, the thickness of the throat of the fillet must also be included in t.

This section also concentrates on acceptance criteria for aligned indications. The following conditions are cause for rejection:

A group of aligned indications with an aggregate length greater than t in a length of 12t unless the distance between the successive imperfections exceeds 6L, where L is the length of the longest imperfection in the group.

Rounded indications in excess of those given in ASME VIII appendix 4. Paragraph (c) gives examination requirements for real-time radioscopic examination. This is not a mainstream NDE technique in the pressure vessel industry so is unlikely to feature in the examination. Ignore it.

10.9.2 UW-52: ‘spot’ RT of welded joints

UW-52 begins with a note explaining the benefits and shortcomings of spot radiography. It basically points out that spot RT is useful for monitoring weld quality but can miss areas with weld defects present. If a weld must not have any defects in it then 100 % RT must be carried out.

Figure 10.6 shows the minimum extent of spot RT as specified by UW-52 (b). Look at these examples on its interpretation (it is fairly straightforward once you’ve got the idea):

  • A single vessel with 55 ft of weld will have two spots examined, one spot for the 50 ft and one spot for the remaining 5 ft.
  • Two identical vessels have 20 ft of weld each. This gives a total of 40 ft and therefore only one spot needs to be taken on one of the vessels.
  • Two identical vessels have 40 ft of weld each. This gives a total of 80 ft and therefore two spots need to be taken (one for the 50 ft and one for the remaining 30 ft). In this case one spot would be taken on each vessel.
  • Three identical vessels have 15 ft of weld each. This gives a total of 45 ft and therefore only one spot needs to be taken on one of the vessels.
  • There are also some more general points on choosing the number and location of the spots.

UW-52 (c) gives acceptance criteria for spot RT. Note how they differ slightly from those in UW-52 for ‘full’ RT. The main points are as follows:

Figure 10.6 ASME VIII (UW-52) spot RT
Figure 10.6 ASME VIII (UW-52) spot RT
  • Cracks or zones of incomplete fusion or penetration are unacceptable.
  • Slag inclusions or cavities with length > 2/3t are unacceptable (the value of t is given in UW-52 (c)(2), which also gives limits on multiple inclusions or cavities <2/3t).
  • Rounded indications need not be considered. (This is an important point . . . these are only relevant when a weld needs full RT.)

Re-test of rejected welds UW-52 (d) deals with re-tests when spot radiographs have failed their acceptance criteria. This uses the simple 2 for 1 principle, similar to that used in other codes (see Fig .10.7). Note the following main points in UW-52 (d):

1. When a spot radiograph is acceptable then the entire weld increment represented by it is acceptable.

2. When a spot radiograph shows a defect that is not acceptable then two additional spots must be examined in the same weld increment at locations chosen by the inspector:

If the two additional spots examined are acceptable the entire weld increment is acceptable provided the defect disclosed by the first radiograph is removed and the area repaired by welding. The weld-repaired area must then be radiographed again. .

If either of the two additional spots examined are unacceptable then the entire increment of weld represented must be rejected and either:

  • Replace the entire weld or
  • Full RT the weld and correct any defects found.

Repair welding must be performed using a qualified procedure and in a manner acceptable to the Inspector. The re-welded joint, or the weld-repaired areas, must then be spot RT examined at one location in accordance with the foregoing requirements of UW-52.

The 2 to 1 Replacement rule

Figure 10.7 RT re-tests
Figure 10.7 RT re-tests
Please go to API 510 Chapter 10 to view the test

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