API 510 Chapter 5

API 510 Chapter 5 Repair, Alteration, Re-rating (Section 8)

API codes are not only about inspection. Since their inception in the 1950s, the in-service inspection codes API 510, 570 and 653 have had the activities of repair, alteration and re-rating as a central part of their content. Worldwide, other in-service inspection codes do not necessarily follow this approach – re-rating, in particular, is uncommon in some countries. Many countries, as a result of legislation, experience or simple technical preference, do not do it at all. Remember, however, that the API 510 exam is strictly about what is in the code documents, not your experience or personal view, so you need to accept the API philosophy as set out in the codes

5.1 Definitions The three important definitions are those for repair, alteration and re-rating. Within the confines of the API codes these three definitions are almost a subject in themselves. They are not difficult – just a little confusing. The easiest way to understand them is to start with the definition of alteration.

Note two points:

  • There are a specific set of circumstances that define the term alteration.
  • If any grinding, cutting or welding activities are done that do not meet the requirements to be an alteration then they are defined as a repair.

The activities that define an alteration are best understood by looking at Fig. 5.1. Note how an alteration must involve a physical change with design implications that affect the pressure-retaining capability (i.e. the ‘pressure envelope’).

Figure 5.1 Vessel alterations
Figure 5.1 Vessel alterations

This is set out in definition 3.2 of API 510 and is fairly easy to understand.

Slightly more difficult to accept is what is not defined as an alteration. Figure 5.2 shows the situation. Examination questions normally revolve around these definitions and may be open- or closed-book types.

5.2 Re-rating This normally involves raising or lowering the design temperatures (MDMT) or design pressure (MAWP), or both. These are several different scenarios that may lead to a re-rating. Figure 5.3 shows the situation. A re-rating may be necessary if a vessel is badly corroded. Serious thinning may require the MAWP to be reduced. Alternatively, if a process change involves a vessel requiring an increase or decrease (i.e. MDMT related) in temperature, then a re-rating will be required to ensure the vessel is safe under the new conditions. An overriding principle is that any vessel subject to an

Figure 5.2 Vessel repairs
Figure 5.2 Vessel repairs
Figure 5.3 Reasons for re-rating
Figure 5.3 Reasons for re-rating

alteration has then to be re-rated. This makes sense as the alteration is, by definition, design related, so any changes in design condition has to be formalized by re-rating the vessel.

Watch out for exam questions about the code edition to which a re-rating is carried out. As a matter of principle, the primary objective is to re-rate a vessel to the latest edition of the code to which it was built (see Fig. 5.4). If this is possible, it will obviously incorporate any improvements in the code that have been introduced since the vessel was built. Codes do develop through time; allowable stress values, for example, may be increased or decreased based on new material developments or experience of failures.

As an alternative, if it is not possible to re-rate to the most up-to-date code edition, then the idea is to re-rate to the edition to which the vessel was built, as long as jurisdiction/ statutory requirements allow it.

You can see the two re-rating scenarios above set out in clause 8.2.1(b) of API 510. Note the mention of code cases


Figure 5.4 Re-rating options
Figure 5.4 Re-rating options


Figure 5.5 The re-rating flowchart
Figure 5.5 The re-rating flowchart

2290 and 2278 – these are the results of two code ‘case study changes’ relating to relevant editions. That is all you need to know for the purposes of the API 510 exams. The other relevant area to look at is Fig. 8.1 of API 510. This is simply a list of steps that must be complied with if you want to rerate a vessel designed to ASME VIII code edition 1968 to pre-1999 to the latest edition of ASME VIII. Figure 5.5summarizes the situation – if you can understand this figure there is no need to worry too much about the wording of API 510 section 8.2.1(b).

Notice how the flowchart of Fig. 8.1 in API 510 works. Remember that the objective is to re-rate a vessel built to a 1968 to pre-1999 ASME VIII code using the revised material properties of the current code edition (e.g. 2007). The chronological steps start from the top centre of the flowchart with the objective being to progress vertically downwards, ending up at the rectangular box nearer the lower right of the page. This is the ‘destination’ box that allows you to legitimately re-rate the vessel to the latest code edition. Note how the vertical steps include things relating to mainly the material properties of strength and toughness (resistance to impact). This is to ensure that older or substandard materials cannot get through. Equally importantly, note the two boxes near the middle of the flowchart where it is necessary to confirm that the material has not been degraded (by corrosion, age-hardening, temper embrittlement, creep, etc.). This can sometimes be the most difficult step to fulfil, as the operational history of plant is so often incomplete. Don’t worry about these practicalities for the API 510 exam – the exam questions are artificially simplified and often just replicate the exact wording in the flowchart ‘boxes’.

5.2.1 What happens after a re-rating?

There are two main issues here: pressure testing and nameplates. Look at API 510 section 8.2.1(d), which mentions pressure testing – it confirms that pressure testing is ‘normally’ required, but not actually mandatory, as you are allowed to substitute it with ‘special NDE’ (section 8.2.1 (d)(2)) as long as this is acceptable to the pressure vessel engineer. If you do perform a pressure test, remember the situation regarding hydraulic test pressure:

  • ASME code edition before 1999: test pressure = 1.5 x MAWP
  • ASME code edition 1999 and later: test pressure = 1.3 x MAWP

he awkward scenario of what to do if you want to re-rate a vessel to a 1999 or later code, when it was built to an earlier (1968 to pre-1999) code with the higher MAWP multiplier, is covered in clause 8.2.1(d). Here the vessel has already been tested to higher than the ‘1999 and later’ 1.3 x MAWP multiplier, so there is no need for an additional test.

Nameplates are fairly straightforward. API 510 section 8.2.2 explains that a re-rating requires an additional nameplate to be fitted (not a replacement). Alternatively, it is acceptable to add additional stamping. Either must be witnessed by the inspector to make the re-rating valid. This is a common examination question.

5.3 Repairs Under the logic of API 510, any welding cutting or grinding operation that does not qualify for being an alteration (see Fig. 5.2) is, by default, classed as a repair. The main objective of API 510 with respect to repairs is to give technical guidelines as to how these repairs may be carried out rather than to specify any restrictive tests associated with them. Looking back to API 510 clause, you can see that a pressure test is not mandatory following a repair – it is at the discretion of the inspector. Surprisingly, it is not absolutely mandatory after an alteration either – clause backs off slightly and says only that it is ‘normally required’. That is not the same as it being mandatory. Expect exam questions to simply refer to the exact wording of these code clauses, rather than requiring you to interpret them or explain the logic behind them.

5.3.1 Repair techniques Over recent code editions, API 510 has persistently increased its technical coverage of vessel repairs. This makes sense as ‘repair’ actually appears in the title of API 510. Most of the additions have been to section 8 – evidenced by the fact that

API 510 Repair, Alteration, Re-rating

Figure 5.6 API 510 section 8: repair issues
Figure 5.6 API 510 section 8: repair issues

it now contains up to seven levels of numbering hierarchy (e.g. clause, leaving it a little out of balance with other sections of the document. As a result of this growth, API 510 section 8 contains a lot of technically valid and useful points – perhaps several hundred of them. The problem is that they are contained in dense clauses of text with few explanatory pictures, so they don’t exactly jump out of the page at you.

Figure 5.6 below is an attempt to summarize the situation. Look how the main issues are divided into four as follows:

  • Temporary versus permanent repairs (which is which)
  • Specific requirements for temporary repairs
  • Specific requirements for permanent repairs
  • Technical requirements (and restriction) of welding techniques – with the objective of avoiding two main generic problems – brittle fracture and excessive heat input.

Figure 5.7 shows some key technical points about weld overlay repairs while Fig. 5.8 shows the API 510 views on approvals and authorization of repairs.

Now try the familiarization questions in section 5.4.

Figure 5.7 API 510 section weld overlay repairs
Figure 5.7 API 510 section weld overlay repairs

Meaning Review of what is to done(

Figure 5.8 Who approves repairs and authorizations?
Figure 5.8 Who approves repairs and authorizations?

5.4 API 510 section 8 familiarization questions


Q1. API 510 section 8.1.1: repairs and alterations
What repair and alteration activities is the API inspector able to authorize alone (before the repair organization starts work)without reference to the engineer?



Q2. API 510 section temporary repairs
Temporary repairs may remain in place past the first opportunity for replacement if:



Q3. API 510 section temporary repairs: fillet welded patches
Generally speaking, fillet-welded patches are unlikely to be suitable for providing a temporary repair to parts for a pressure vessel containing:



Q4. API 510 section temporary lap band repairs
The circumferential fillet welds attaching a lap band repair to a vessel shell should be designed with an assumed joint efficiency of:



Q5. API 510 section flush insert plate repairs
Flush insert patches may be used to repair corroded shell plates as long as:



Q6. API 510 section weld overlay repairs
A weld overlay repair stands ‘proud’ of the surface of the vessel shell. The inspector should:



Q7. API 510 section repair to P3, P4, and P5 stainless steels
Weld repairs to P3, P4, and P5 stainless steels in any service require specific UT testing for:



Q8. API 510 section PWHT
The API 510 approach to PWHT is that:



Q9. API 510 section local PWHT
What is the minimum preheat that must be maintained during a repair that will have local PWHT?



Q10. API 510 section preheat method in lieu of PWHT
CD welding in lieu of PWHT can only be used on:


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