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

1.

Q1. ASME Section V Article 2: radiography T-223
When performing a radiograph, where is the ‘backscatter indicator’ lead letter ‘B’ placed?

 
 
 
 

2.

Q2. ASME Section V Article 2: radiography T-277.1 (d)
Wire IQIs must be placed so that they are:

 
 
 
 

3.

Q3. ASME Section V Article 6: penetrant testing T-620
Liquid penetrant testing can be used to detect:

 
 
 
 

4.

Q4. ASME section V article 1: T-150
When an examination of the requirements of section V is required by a code such as ASME B31.3 the responsibility for establishing NDE procedures lies with:

 
 
 
 

5.

Q5. ASME Section V Article 6: penetrant testing mandatory appendix II
Which penetrant materials must be checked for the following contaminants when used on austenitic stainless steels?

 
 
 
 

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

1.

Q1. ASME Section V Article 7: magnetic particle testing T-720
Magnetic particle testing can be used to find:

 
 
 
 

2.

Q2. ASME Section V Article 7: magnetic particle testing T-720
During an MT procedure, maximum sensitivity for finding discontinuities will be achieved if:

 
 
 
 

3.

Q3. ASME Section V Article 7: magnetic particle testing T-741.1 (b)
Surfaces must be cleaned of all extraneous matter prior to magnetic testing. How far back must adjacent surfaces to the area of interest be cleaned?

 
 
 
 

4.

Q4. ASME Section V Article 7: magnetic particle testing T-741.1 (d)
According to ASME V, what is the maximum coating thickness permitted on an area to be examined by MT?

 
 
 
 

5.

Q5. ASME Section V Article 7: magnetic particle testing T-764.1
Which of the following methods can verify the adequacy of magnetic field strength

 
 
 
 

6.

Q6. ASME Section V Article 7: magnetic particle testing T-762(c)
What is the lifting power required of a DC electromagnet or permanent magnet yoke?

 
 
 
 

7.

Q7. ASME Section V Article 7: magnetic particle testing T-752.2
Which types of magnetizing current can be used with the prod technique?

 
 
 
 

8.

Q8. ASME Section V Article 7: magnetic particle testing T-752.3
What is the maximum prod spacing permitted by ASME V?

 
 
 
 

9.

Q9. ASME Section V Article 7: magnetic particle testing T-755.1
What is the best description of the limitations of yoke techniques?

 
 
 
 

10.

Q10. ASME Section V Article 7: magnetic particle testing, appendix 1
Which MT technique is specified in ASME article 7 mandatory appendix 1 to be used to test coated ferritic materials?

 
 
 
 

11.

Q11. ASME Section V Article 23: ultrasonic thickness testing, section 5.1
UT thickness checking using standard equipment is used for temperatures up to:

 
 
 
 

12.

Q12. ASME Section V Article 23: ultrasonic thickness testing, section 8.5
Special ultrasonic thickness measurement equipment can be used at high temperatures. If the equipment is calibrated at ambient temperature, the apparent thickness reading displayed at an elevated temperature should be:

 
 
 
 

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