New to API 510 BoK
Starting with the September 2022 API 510 examinations, the API 510 BoK includes thirteen of the thirty-six articles included in ASME PCC-2 Repair of pressure equipment and piping: 2018 edition. Increasingly, API 510,570 and 653 cross-reference PCC-2 for issues relating to repairs, alterations and pressure testing. Both API 510 and PCC-2 have the status of post-construction codes however as API 510 is the ‘governing code’ for the 510 exam, its content takes priority over that of PCC-2 if there are any minor inconsistencies.
The construction code as reference
API 510 and PCC-2 frequently refer to the requirements of ‘the construction code’ (e.g. ASME VIII-I for vessels) for fabrication details, NDE extent, PWHT and whether a pressure test is mandatory. This is unchanged as a result of including ASME PCC-2 articles into the BoK. API ICP exams are written using the principle that PCCs are used if following the construction code is not possible. Fillet-welded patches and PWHT replacements are good examples.
The PCC-2 articles: 2018 edition
The table below shows the PCC-2 articles included in the API 510 BoK starting with September 2022 exam cycle. A couple of articles are new/heavily revised for the 2018 edition, whilst most have remained virtually unchanged for the past few editions. Note the following points about the effect of their inclusion in the API 10 BoK
• Most of the Articles just clarify and explain the requirements for repairs/alterations already included in API 510 rather than adding anything fundamentally new. Examples are:
Flaw excavation On-stream repair welding/hot tapping Weld build-up and overlay CDW alternative to PWHT Pressure testing NDE in lieu of pressure testing
• A few Articles add new requirements not addressed fully in API 510. Examples are Butt-welded insert plates Fillet welded patches Flange repair and conversion (from ring-type to raised-face flanges) Inspection/repair of shell/tube heat exchangers
It seems unlikely there will be any major shift in 510 exam question content as a result of including PCC-2 in the BoK. Technical points suitable for new exam questions are included in the explanations and sample question sets for each article following
ASME PCC-2, Repair of pressure Equipment and Piping
ATTN: Test questions will be based on the following portions of the document only:Article 201: Butt-Welded Insert Plates in Pressure ComponentsArticle 202: External Weld Build up to repair Internal ThinningArticle 209: Alternatives to Post weld Heat TreatmentArticle 210: In-Service Welding Onto Carbon Steel Pressure Components or PipelinesArticle 211: Weld Build-up, Weld Overlay, and Clad RestorationArticle 212: Filet Welded PatchedArticle 215: Repair Welding Considerations for Cr-Mo Steel Pressure VesselsArticle 216: Welded Hot Taps in Pressure Equipment or PipelinesArticle 304: Flaw Excavation and Weld RepairArticle 305: Flange Repair and ConversionArticle 312: Inspection and Repair of Shell and Tube Heat ExchangersArticle 501: Pressure and Tightness of Piping EquipmentArticle 502: Non-destructive Examination in Lieu of Pressure Testing for Repairs and Alternations
Sample questions and answers
Included in each article summary below are three sample questions. Try each question open-book; there is little point in just guessing the answers. To see how you did, click on the answers link.
Article 201:Butt-welded insert plates in pressure components
Art 201 gives technical details of flush ‘insert’ patches. The inserts may contain nozzles and are suitable for vessels, piping and tanks and accepted by API 510/570/653 as permanent repairs. ASME PCC-2 doesn’t differentiate between permanent and temporary, just provides technical details. Key BoK points relate to:
• Shapes/thickness limits for the inserts• Minimum spacing to other inserts/ existing welds• Limits on forming (bending) the inserts to fit the pipe/vessel• NDE and pressure testing
Fabrication details are chosen to minimise stress concentrations and interaction of HAZs which would cause local hardening and embrittlement. As with most PCC-2 articles, the extent of NDE and PWHT defaults to that required by the original construction code.
Try these sample questions.
Qu 1. Which of these situations is not covered by PCC-2 Article 201?
a) Insert plates of dissimilar material to the parent plateb) Replacement of a full butt-welded shell coursec) Insert plates thicker than the parent materiald) Insert plates containing nozzles
Qu 2. What is the minimum acceptable corner radius of a butt-welded rectangular insert plate 1in (25mm) thick if the parent material is 0.9in (23mm) thick?
a) 1in(25mm)b) 2in (50mm)c) 3in(75mm)d) 6in(150mm)
Qu 3. Which welding technique should not be used for single-sided butt welds on an insert plate?
a) FCAWb) SMAWc) GTAWd) GMAW (S-C)
To see how you did, click on the answers link.
Article 202: External weld build-up to repair internal thinning
Art 202 gives technical details of weld build-up on an external surface to restore strength to a component that has internal thinning. It is mainly applicable to piping where it may be impossible to access the inside for adding weld-build up there. It supplements Article 211 which also covers weld build-up, overlay and cladding. Key BoK points are
• The length of the external overlay and how much it overlaps the internal thinned areas (see fig 202.3.1)• ‘Prequalified’ designs that can be used without a detailed engineering analysis• Proof and burst tests are needed when the overlay design is not ‘prequalified’. These are complicated and probably not suitable for API exam questions.• Welding techniques to avoid burn-through of the thinned component• Volumetric NDE and pressure testing
Qu 1. Internal thinning on a 20in (508mm) OD pipe of nominal thickness 0.75in (19mm) is to be repaired by weld-build on the external surface. If the length of thinning is 6in (152mm), what is the minimum length of full-thickness weld build-up (excluding taper)?
a) 52.1mmb) 152mmc) 256.2mmd) 309.8mm
Qu 2. Internal thinning on a 10in (254mm) OD pipe of nominal thickness 0.5in (13mm) is to be repaired by 0.3in (7.6mm) weld-build on the external surface. If the length of thinning is 4in (100mm), what is the maximum acceptable corner radius of the weld build-up?
a) There isn’t oneb) 7.6mmc) 13mmd) 50mm
Qu 3. Which of these is not a prequalified design for weld build-up repairs and so needs an engineering evaluation?
a) A schedule 60 straight piping sectionb) The maximum thinning length is half the nominal outside diameterc) A design temperature of 350 DegCd) All of the above
Article 209: Alternatives to PWHT
There is little ‘new’ in Article 209 that is not already covered in API 510 (and now also in the mandatory appendices of ASME VIII-1). Table 209(4.1.1) lists all relevant cross-references for the use of PWHT alternatives, including elevated preheat and CDW. There are no additional sample questions needed for Article 209 as it is adequately covered in API 510 and RP 577.
CDW as a repair technique
Controlled Deposition Welding (CDW), also called temper-bead welding, is an accepted technique for repair welding without construction-code post-weld heat treatment (PWHT) accepted by API and other PCCs. It works by laying down successive beads of weld, each providing grain-refinement to the bead underneath, replacing partially the effects of PWHT. There are two variations
• Full-bead technique: no grinding between subsequent beads• Half-bead technique: partial grinding of each bead weld cap before the next is added
CDW has many restrictions. If used for the wrong materials or without care of critical factors, it can be worse than no PWHT at all. Critical factors are
• It can only be used for P-1, P-3 or P-4 materials. In higher alloys, it causes brittleness• CDW provides some grain refinement (like PWHT) but is poor at stress relief. It’s risky for high-stress areas or with Hydrogen-initiated cracking (HIC) or wet H2 DMs.• It needs a WPS/PQR to get the correct welding parameters• WPSs can be difficult to follow if access is poor
The importance of weld hardness
HAZ hardness is the key criterion of a CD weld, as it influences impact (notch) toughness. The summary of many literature sources is
CDW can achieve grain refinement (at best) 80-85% of that of full PWHTAndIt is easy to worsen this by incorrect technique
The table shows typical hardness results achieved with CDWs compared to the un-welded base material. Note the wide variability, even under workshop conditions.
Owing to the variability, codes don’t quote fixed CDW acceptance limits. Some users accept a limit at the upper end of the range, and others trust the PQR results will transfer to the real weld.
Use API 510 for guidance
An excellent distillation of the results of all the research work on CDW is the guidelines in API 510 (22.214.171.124.3.3). It helps achieve the best possible (never perfect) replacement for PWHT on carbon steel and low-alloy materials. Two vital points are
• The need for a CDW metallurgical review; CDW is too variable to ignore.• Qualifying the CDW using a WPS/PQR
Article 210: In-service welding onto carbon steel pressure components/pipelines
This covers welding to a system that has fluid flowing in it and links to Article 216 on hot tapping. Most of the article is about welding techniques to avoid burn through and hydrogen cracking; the two biggest problems with on-stream welding (mainly piping and pipelines). Weld build-up of thinned surfaces may be needed to provide reinforcement before other welding occurs.
It covers the idea of %age Carbon Equivalent (CEq) as an indicator of how easy a material can be welded without becoming brittle. This is the same as in API RP 577.
Many in-service welds need prequalification (PQR) to prove their validity before use. It follows the principles of ASME IX, but fig (210- 126.96.36.199) shows how many destructive bend tests are required. Hardness measurements across the HAZ are important (note this is slightly different to the method described in API RP 577).
Qu 1. The two main concerns about in-service welding onto carbon steel pressure components are burn through and
a) Lack of fusionb) Welder safetyc) Low carbon equivalentd) Hydrogen cracking
Qu 2. Who decides if a PQR is necessary for an on-stream welding technique?
a) Owner-userb) Welding inspectorc) API inspectord) Owner-user or welding engineer
Qu 3. When can an on-stream weld procedure (PQR) qualified on lower carbon equivalent material be used in a repair application on a higher carbon equivalent material?
a) If the cooling rate is less than for the PQRb) If the cooling rate is greater than for the PQRc) For low alloy steeld) It can’t
Article 211: Weld build-up, weld overlay and clad restoration
Note the four different techniques covered in his article, (the definitions make good exam questions)
• Weld overlay is the application of corrosion-resistant weld metal on carbon steel or low alloy base metal.
• Weld build-up is the application of carbon steel or low alloy weld metal, applied for the purpose of restoring base metal thickness.
• Clad Restoration is the application of corrosion-resistant weld metal on carbon steel or low alloy base metal, for the purpose of restoring the original corrosion-resistant weld overlay or cladding. The original cladding could have been applied by methods such as roll bonding or explosion bonding.
• Back Cladding is the application of corrosion-resistant weld metal on carbon steel or low alloy steel weld in clad material that has been repaired.
Much of the article covers the welding techniques to obtain good fusion and avoid embrittlement and cracking. There are special requirements for low alloy steels involving dehydrogenation and/or PWHT. Specific tests involved are ferrite/ferricyanide testing for stainless steels and Alloy 400 Nickel alloys. Owing to the complexity of these, they are most suited for an occasional open-book exam question.
Qu 1. The application of carbon steel or low alloy weld metal, applied for the purpose of restoring base metal thickness, is termed
a) Weld overlayb) Weld build-upc) Claddingd) Back cladding
Qu 2. Which surfaces of vessels or piping does Article 211 refer to?
a) External surfaces onlyb) Internal surfaces onlyc) Internal or external surfacesd) Internal or external surfaces that have not been previously repaired
Qu 3. When performing weld overlay or back-cladding, when is more than 1 weld layer required?
a) Alwaysb) When the total depth of back cladding exceeds 1/8in ( 3mm)c) When CDW is usedd) If there is no PQR qualified
Article 212: Fillet-welded (lap) patches
Permanent or temporary?
Fillet-welded lap patches are accepted as permanent shell repairs by API 653 (storage tanks) but only as temporary by API 510 (vessels) and API 570 (piping). Three things get lap patches a bad reputation
• They superimpose tricky bending stresses on easy-to-calculate membrane stresses. That’s why they aren’t normally used in the pressure envelope.• They have a low weld joint efficiency (0.45 to 0.7) and a maximum allowed thickness. Hence, many lap patches need to be of stronger material than the parent to meet their trequired.• They introduce a crevice for the process fluid to corrode.
These are undesirable, but not insurmountable, problems, so lap patches find many uses in plant repairs. Temporary repairs sometimes end up being permanent.
Post-construction codes place restrictions on size and spacing to limit lap-patches disadvantages to manageable levels. It’s easy to find lap-patch repairs that break these rules and haven’t failed yet, but they’re good guidelines to follow. These patches are only suitable for service temperatures above the nil-ductility temperature of the materials, up to a maximum of 345°C (650°F).
Article 212 gives calculations for sizing lap patch ‘overlaps’, thickness and perimeter welds and tapers. These are generally too complicated to form API ICP exam questions. More applicable are straightforward questions (open- or closed-book) about the principles of:
• Spacing from nearby welds or structural discontinuities• NDE of the repair• Pressure testing ( if specified by the original construction code)
Try these sample questions
Qu 1. When may fillet-welded (lap) patches be used to cover areas containing a crack-like flaw?
a) The flaw has been analysed using an FFS studyb) If the flaw is just a grinding markc) If the material is ductile and not in the creep ranged) Never
Qu 2. When applying a fillet-welded lap patch over a thinned area, the patch must?
a) Have full penetration butt weldsb) Overlap the thinned area by a minimum of 1in (25mm)c) Be attached by at least two weld-runsd) Be no more than 10in (254mm) in its longest dimension
Qu 3. When adding a lap patch of thickness t to a curved vessel or pipe of Diameter D, what is the maximum separation gap allowed?
a) 10% of tb) 1% of Dc) 1/16in (1.5mm)d) 3/16in (5mm)
Article 215: Repair welding Cr-Mo steel vessels
This is a completely new PCC-2 Article added in the 2018 edition. Most of PCC-2 is about the repair of plain carbon and low-alloy steels, so this addresses Cr-Mo steels used in refinery and power generation boilers, heaters and piping. Cr-Mo materials suffer specific DMs (hydrogen embrittlement, temper embrittlement, high-temperature hydrogen attack and creep) at their high operating temperatures that can cause problems with weld repair. Key points are
• Typical materials are 1Cr-0.5Mo, 1 ¼ Cr – 0.5 Mo,2 ¼ Cr – 1 Mo, up to 9Cr – 1 Mo• Repair welds require specific PQRs to ensure their validity• Temperature input must be carefully controlled to prevent embrittlement• PWHT must be carefully chosen
Qu 1. Which of these is not a Damage Mechanism commonly suffered by Cr-Mo pressure vessel steels?
a) Creep embrittlementb) Temper embrittlementc) Sulphidationd) Hydrogen attack
Qu 2. Which of these is not covered in PCC-2 Article 205?
a) Repair of creep-damaged Cr-Mo steelsb) Repair of cracked Cr-Mo steelsc) Repair of hydrogen-degraded Cr-Mo steelsd) Repair of 3Cr-1Mo steels
Qu 3. Repairs to Cr-Mo vessels by adding a welded sleeve are?
a) Prohibitedb) Acceptable if they are correctly designedc) Permanentd) Temporary
Article 216: Welded hot tapping in pressure equipment/pipelines
SummaryThis is a long article that supplements API 2201 Hot Tapping, mentioned in API 510/570 PCCs. It also links with PCC-2 Article 210 In-service welding, as this is involved in the hot tapping procedure. Points that make sensible API ICP exam questions are
• Where hot tapping should not be used, mainly to avoid explosion risk (sec 2.4)• Special precautions (mainly safety-related)• Restrictions on hot tap location; e.g. proximity to existing welds (sec 3.6)• Wall-thicknesses to prevent welding burn-through (sec 3.11 and 4.1)• Pressure testing of hot tap fittings
Qu 1. Who must approve the written procedure for a hot tapping operation?
a) The hot tapping contractorb) The welding engineer and API inspectorc) The owner-userd) All of the above
Qu 2. Which of these is not suitable for a hot-tapping operation?
a) A pipeline containing highly flammable gasb) Carbon steel containing hydrogen-rich process fluid at 250 degCc) Stainless-steel pipingd) Material that does not require PWHT
Qu 3. Which of these are not normally suitable for hot tapping?
a) Vessels under external pressureb) Vessels under cyclic internal pressurec) Pressurised storage tanks with no material notch-toughness requirementsd) Kerosene (gas oil) pipelines
Article 304: Flaw excavation and weld repair
This is a short article in PCC-2 Part 3 Mechanical Repairs. In many cases, component wall thinning or cracks can be ground out (excavated) and left unwelded if the remaining thickness is greater than tmin. Key points that make good ICP exam questions are about
• Methods of excavation that do not leave hardened (embrittled) cut edges• NDE on the excavation before leaving as-is, or filling with weld• Using WPSs and PQRs if weld deposition
Most of the points are recognised as ‘good engineering practice’ and also found in API 510/570, API RP 577 and construction codes.
Qu 1. What is required before arc-gouging defects out of a material that requires PWHT in the construction code?
a) PWHTb) Preheatc) Flap-wheel of the surfaced) Surface peening
Qu 2. What taper should be used when excavating a defect, leaving thickness lower than t min?
a) Any taperb) 5:1c) 4:1d) 3:1
Qu 3. Which standard covers markings for identifying grinding wheels?
a) ANSI B74.2b) ANSI B7.1c) ANSI B74.13d) ANSI B16.25
Article 305: Flange repair and conversion
Flange face defects cause leakage so for new and repaired flanges, typically raised face (RF) types, tolerances are specified for
• Surface flatness (in micro-inch/micrometres) of the mating face• Profile of the concentric or spiral groove pattern• Seating width
All are necessary for a tight seal without over-tightening the flange bolts. In use, corrosion or fretting of the flange face cause defects. Faces can be re-machined within hub-thickness tolerances.
Some defects are acceptable
Defects within a proportion of the gasket seating width and below a certain depth can be acceptable without re-machining. Commonly used codes are ASME PCC-1 Guidelines for pressure boundary bolted flange joint assembly and TEMA (Tubular Exchanger Manufacturers Association) standard for heat exchangers.
PCC-2 Article 305 explains limitations and precautions when doing welded repairs to flange faces. Flange construction code e.g. ASME B16.5 give minimum hub thicknesses. Most flanges have sufficient over-thickness to allow several machinings. If a hub is machined too thin, it bends (rotates) during bolt-tightening, causing leaks.
Flange conversionArticle 305 explains the (relatively uncommon) technique for converting a ring-type joint flange into a raised face flange by welding up the ring groove, re-machining, and checking by NDE.
Qu 1. If a raised face flange is machined or refinished, what is the minimum acceptable height of the raised face?
a) 0.8mmb) 3mmc) As per the code requirements of ASME B16.5d) As per the code requirements of ASME B16.5 or TEMA
Qu 2. What code covers tolerances on the flatness of flange faces?
a) ASME B16.5b) API 650c) ASME PCC-2d) ASME PCC-1
Qu 3. What is the maximum flange-face roughness for a ring-type joint (RTJ)?
a) 6.4 µm (250 µin)b) 3.2 µm (125 µin)c) 1.6 µm (63 µin)d) 0.8 µm (32 µin)
Article 312: Inspection and repair of shell/tube heat exchangers
Article 312 is a little unusual in applying only to shell-and-tube heat exchangers. API 510/570 Cross-reference it as well as the TEMA (Tubular Exchanger Manufacturers Association), itself unusual in providing rules for both construction and in-service use. Art 312 refers to in-service use only and covers the steps of
• Inspecting the tubes and tube plate (specific NDE methods such as ET, PSET, IRIS)• How many tubes to inspect as a representative sample• Plugging and sleeving of damaged tubes• Weld repair of tube plate• Pressure testing after repairs
There is a detailed fig (312- I-1.3) showing the effectiveness of the different NDE techniques. Much of this article is too detailed for closed-book ICP exam questions, but open-book question answers are fairly easy to track down once you’ve determined the question is about heat exchangers (there are no technical details on exchanger inspection in API 510 or 570).
Qu 1.What is the maximum shell-side operating pressure for which a friction-fit tapered tube-plug can be used on a shell and tube heat exchanger?
a) A pressure equal to the tube-side operating pressureb) 100 psi(0.75MPa)c) 200 psi (1.5 MPa)d) There is no maximum, provided the plugged tube is pierced
Qu 2. Which of these NDE is most suited for inspection of non-ferromagnetic tubes?
a) ETb) RFETc) PSETd) MFL
Qu 3. What is the minimum of tubes that should be inspected on an exchanger containing 500 tubes?
a) 50b) 100c) 125d) All of them
Article 501: Pressure and tightness testing
What’s the point?Pressure (normally hydro) tests detect leaks after new construction or repair and are covered in some detail in API 510/570. Pressure tests are a crude measure of strength, but often the code-specified test pressure is not high enough to cause the failure of a seriously weakened component because
• Hydrotests impose static pressures only, not impact or operating loads• Equipment factors of safety are high, so hydrotests don’t exert failure-inducing loads• Many crack-initiating weld defects can easily pass a hydrotest
API 510/570 say when a hydrotest is needed using three terms
• At the inspector’s discretion (i.e. optional)• Normally required (not the same as mandatory)• Mandatory.
Mandatory hydrotests are mainly for new construction, where there’s a possibility of major design/material errors or systemic welding problems.
Where a hydrotest is a good idea
Situations where a hydrotest is a good idea, even if not code-mandatory, are:
• When there’s a risk of brittle fracture owing to material substitutions• Components with tube-to-tube plate expansions or welds• Hasty repairs with unconvincing weld procedures, qualifications or material ID• Difficult-to-weld nickel alloys• Welds on castings.
Article 501 coverage
Art 501 gives general technical information on pressure, but remember it does not take priority over the content of API 10/570 in ICP exam questions. Where 510/570 cross-references the pressure testing requirements of the construction code (ASME VIII-I or B31.3), Art 510 just repeats these requirements, i.e. contains nothing new. Tests described are
• Hydrotest• Pneumatic test• Low pressure (bubble) leak test• Tightness test
The dangers of pneumatic testing are emphasised, elaborating on the content of 510/570. Mandatory appendix 501-II gives detailed methods for calculating blast damage and exclusion areas for pneumatic tests. These are too complicated for ICP exam questions.
Qu 1.Pressure testing after repair welding may provide?
a) A guarantee of fitness-for-serviceb) Some stress relief at stress concentrationsc) An alternative to design proof testingd) All of the above
Qu 2. What types of pressure tests should be performed after weld repairs on an existing vessel?
a) Hydrotestingb) Pneumatic testingc) Hydrotesting and leak ‘tightness’ testingd) Whatever was specified for initial construction
Qu 3. After a weld repair on an existing vessel with a MAWP < 200psi a pressure test is?
a) Optionalb) Not requiredc) Only required if the repair welding has not had PWHTd) Mandatory
Article 502: NDE in lieu of pressure testing for repairs and alterations
Using NDE in lieu of pressure testing after repair/alterations are allowed in API 510/570/653 under various situations. The general principle is that NDE can be used if pressure testing is impractical/impossible or, can give an equivalent or better assurance of integrity, given the expected damage mechanisms.
Art 502 makes reference to the pressure-testing exemptions of NB-23 (National Board Inspection Code).NB-23 is mentioned in API 510 but is not included in the 510 or 570 BoKs, you just need to know of its existence.
Qu 1.NDE of a repair/alteration sometimes give better assurance of integrity than a pressure test, when?
a) Allowable stress of the material is a concernb) A repair or alteration has been majorc) Crack initiation is a concernd) Material deficiencies cannot be ruled out
Qu 2. Pressure testing of a repaired item is primarily to determine?
a) Structural integrityb) Leak tightnessc) Material strengthd) All of the above
Qu 3. Pressure-testing an item in-service that has already been pressure-tested during construction gives little assurance of?
a) Resistance to brittle fractureb) Leak tightnessc) Absence of sub-critical flawsd) Structural integrity
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