Burst Testing Rules
There are many ASME rules covering burst testing originating in many different code books. A successful burst test requires the use of the correct code book, and the correct method within the code book.
Stainless Steel: Do not strain, brittle coat or displacement test stainless materials (Except for HLW hot water heaters). Many code references are confusing. In multiple codes direct contradictions can be found in what tests are allowable for which materials. This can be found in ASME VIII, I, and IV with regards to materials without a “sharp kneed” portion of the stress-strain diagram (generally a description of stainless steel). Also watch out for restrictions on the ratio of ultimate to yield stress being below 0.625. When dealing with the CRN system, it is important to find all the contradictions and take the most conservative approach possible. Sometimes this leads to ridiculous outcomes like the stainless burst tests for ASME IV commented below, but your submission will be reviewed by multiple reviewers across Canada, and only the most conservative interpretations will survive both the original submissions and re-submissions at time of renewal 10 years later for fittings. Manufacturers with existing CRNs based on brittle coat testing of stainless have been required to re-test their parts using burst methods to maintain their existing CRNs.
This is the most commonly referenced code book for burst testing. Rules are found in UG-101. Important sections include:
Duplicate Parts: UG-101(d)(1) – You have finished a burst test for one material, how many other materials can the results be applied to? This section allows results to be used on other materials with the same P number as long as it is stronger than the material tested.
Geometrically Similar Parts: UG-101(d)(2) – How many tests do you need to prove a range of parts? This is different from the usual method of 3 burst tests across a range of sizes used for many CRN applications, and can lead to registration difficulties depending on how closely the reviewer wants to stick to ASME pressure vessel requirements for products that are registered as fittings.
Corrosion Allowance: UG-101(i) – Your burst test was done on a new part but you have a corrosion allowance – here is how to correct the calculated rating.
Yield and Tensile Test: UG-101(j) – This section is most commonly ignored – the code requires multiple physical tests, not the 1 or 2 often performed (often from the MTR). This sometimes leads to registration issues.
Elevated Temperatures: UG-101(k) – How to correct your burst test results for design temperatures above the test temperature.
Brittle Coat Testing: UG-101(l) – The first of many allowed test methods. Brittle coat testing is seldom used for VIII-1 applications. See comments on stainless steel above.
Burst Testing: UG-101(m) – The most commonly used test method involving simple testing under elevated pressures. No the test does not need to go to destruction, but the test pressures are often a surprising 6-7x design pressure once all the correction factors for material strength and temperature effects are included. The pressures can be even higher if correcting for weld efficiencies and corrosion allowances.
Strain Testing:UG-101(n) – A more complex test method with lower test pressure requirements. Not used very often. See comment on stainless steel above.
Displacement Testing: UG-101(o) – Another more complex method with lower test pressures. Also not used very often. See comment on stainless steel above.
External Pressure: UG-101(p) – What to do for shapes that can collapse under the pressure load. This is a 3x pressure test where the test pressure is in the same direction as the external pressure load. A special test chamber might be required to successfully apply the test pressure to the outside of the object under test.
The HG section of the code provide 4 methods of testing:
Strain Tests: HG-502.1 – A complex method of testing using strain gauges to prove that the design did not hit the yield point. See comments on stainless above.
Displacement Tests: HG-502.2 – Another complex method of testing using dial gauges. Again to prove that the design did not hit the yield point. See comments on stainless above.
Bursting Tests: HG-502.3 – A simple method of proving that a design is safe by pressurizing it until it fails. This is more conservative than other more complex tests.
Brittle Coat Test: HG-502.4 – A procedure of coating a product with a brittle coating – usually lime, and pressurizing it until the coating flakes off. It is both simple and less conservative than the burst test making it the favorite test method. See comments on stainless above.
Duplicate Parts: HG-504 – This standard restricts the use of test results from one design on to similar parts. We see manufacturers running tests on every design or material variation.
Proof Test: HLW-502 – Section HLW has different requirements for burst testing from section HG – only the brittle coat procedure (like HG-502.4 is allowed), regardless of use of stainless material. We have seen interesting situations where manufacturers of stainless boilers must burst once to HG-502.3 and a second time to this section if the product is to be CRN registered to both HLW and H stamp use.
Burst testing rules for Section I are found in A-22. Two methods are provided based on yielding (strain and displacement) and one on bursting the part:
Yield Point: A-22.5 – For a yielding based test (strain or displacement testing), the yield point must be “sharp kneed”. Our current understanding is that this precludes strain or displacement testing of stainless steel parts. See comments on stainless steel above. Also watch out for the restrictions imposed by A-18.104.22.168 on the difference between the yield and tensile point.
Strain Testing: A-22.6.1 – A test based on measuring the strain in a part to prove that it did not yield under test. See A-22.5.
Displacement Testing: A-22.6.2 – A test based on measuring displacement to prove that yielding did not occur. See A-22.5.
Burst Testing: A-22.6.3 – Useful for any material in ASME Section I. Refer to comments in ASME VIII-1 UG-101(m).
Parts Subject to Collapse: A-22.7 – Parts subject to external pressure can be proof tested at 3x the design pressure.
Duplicate Parts: A-22.9 – Tests on one material are not transferable to other materials. Geometrically similar parts can be proven based on “a series of tests covering the complete range of the pressure part”. Unfortunately, the number of tests, and the method of proving that the range has been certified is not provided. ASME VIII-1 UG-101(d)(2) provides some guidance that might be acceptable for ASME I CRN use.
B16.9 fittings are used as if they are pipe (the end user runs pipe calculations before using them). It is up to the manufacturer to prove that the fitting actually is the same strength as pipe. They have the choice of proving this through calculation or burst testing. Section 9 covers how the burst testing is to be done. Points of Interest:
Test Procedure: 9.3 – The required test results to prove that the fitting can be rated as a certain schedule pipe. Testing is done by pressurization, but does not have to proceed to destruction.
How Many Tests: 9.4 – B16.9 allows much more applicability or scaling of results from one material / size / thickness to other fittings compared with other ASME codes. Some CRN reviewers are nervous of any rules that are more lenient than ASME VIII-1 UG-101(d)(2) which specifies how many tests are required for pressure vessel code.
“The pressure design of components not covered by the standards listed in Table 126.1 or for which design formulas and procedures are not given in the Code shall be based on calculations consistent with the design criteria of this Code. These calculations shall be substantiated by one or more of the methods listed below” (104.7.2):
Experience: 104.7.2(A) – See B3.13 below – this is never acceptable.
Experimental Stress Analysis: 104.7.2(B) – we have never seen this used.
Burst Testing: 104.7.2(C) – Burst testing done to MSS SP-97, ASME B16.9, or ASME I A-22. See comments below for B31.3, it is probably best to do the tests to ASME I A-22.
Detailed Stress Analysis: 104.7.2(D) – Stress analysis like Finite Element Analysis (FEA). Although this method can be used, jurisdictions often require the analysis to be validated using burst test, strain or displacement testing. Using FEA without physical testing is normally allowed to prove the cycle life of a component.
Related Components: 104.7.2 – “It is permissible to interpolate between sizes, wall thicknesses and pressure classes and to determine analogoies among related materials.” Unfortunately how to determine material analogies and how many samples are required to interpolate sizes or thicknesses is not specified. ASME VIII-1 UG-101(d)(2) provides some size guidelines that most Canadian reviewers are acceptable with. VIII-1 UG-101(d)(1) limits like materials to materials with the same P number.
“Pressure design of unlisted components to which the rules elsewhere in [the B31.3] code book can be proof tested according to the rules of [B31.3]”. Available methods include:
Experience: 304.7.2(a) – Although the code book allows for the use of “extensive, successful service under comparable conditions with similarly proportioned components of the same or like material.” this is NEVER allowed in Canada under the CRN system. We get asked this all the time – the answer is no! The successful service history of a product is ignored in the CRN system.
Proof Testing: 304.7.2(c) – Proof testing can be done under ASME B16.9, MSS SP-97, or most commonly ASME VIII-1. Be cautious when choosing which standard to use. Although B16.9 allows the most lenient applicability of results from one material or size to another, it is prudent to use the more conservative VIII-1 requirements. The important point is that your results must be acceptable to all reviewers in Canada now and ten years from now for your fitting renewals. We experience no problem registering B31.3 fittings when ALL VIII-1 UG-101 requirements are followed. We have never used the methods of MSS SP-97.
Alberta Rules (Added Oct 10 2014)
Alberta has released document 00370159.DOC.1 “PROOF TESTING REQUIREMENTS” which we expect to reduce the variation in requirements between reviewers. This document could also be considered a guideline when registering with other provinces, but is only officially recognized in Alberta. This is not on the ABSA website, but you can request a copy of it. Here it is copied in full:
Proof Test Requirements
When the pressure rating of a component can’t be established by design calculations proof testing in accordance with UG-101 (m), Section VIII, Div. 1 shall be used.
The Proof Test Report shall be documented and include:
- Present complete calculations for the MAWP or Burst pressure as per UG-101(m)(2), considering the actual and specified mechanical properties;
- Identify the tested part by drawing and revision number, size or designation, and complete material specification;
- Identify the test method and equipment used, and provide the test gauges # and last calibration date;
- Identify the pressure at which the test was stopped and specify the reasons and observations;
- The Test Report shall be signed by: Manufacturer’s representative and by a Provincial Authorised Inspector (if test done in Canada) or a National Board commissioned Authorized Inspector (third party).
- A copy of the A.I’s National Board card (both faces) shall be provided;
Other required documentation to support the Proof Test Report:
- Calculations, as required, to account for usage at higher temperature and corrosion allowance, see UG-101(i) and (k);
- The drawing of the tested part, must identify the part# and complete material specification;
- Where the tested part is too small to permit obtaining 3 tensile specimen samples, then the Material Test Report (MTR) data may be used;
- A copy of the Material Test Report of the tested part. This document must identify the Heat/Cast/Lot# and the part/drawing# of the part).
NOTE: to achieve the required proof test pressure the proof tested assembly may require modifications or adaptations to avoid leakage. Please consult ABSA’s Design Survey with respect to the proof test assembly and any modifications or adaptations and obtain the approval, before starting the testing.
Our comments: “Where the tested part is too small to permit obtaining 3 tensile specimen samples, the the Material Test Report (MTR) data may be used” is a considerable relaxation on previous ABSA requirements, and goes a long way toward making small products manufactured from sheet like compact heat exchangers easier to register. Very few reports include information on the Authorized Inspector other than endorsement number and signature. Copying both sides of the N.B. card is not usually done.