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.
When dealing with the CRN system it is important to think beyond the first registration. Will the burst test report be acceptable in other provinces? Will it be acceptable in ten years when it is time for renewal? It is important to find all the differences and take a conservative approach.
Caution on Stainless Steel: Do not strain, brittle coat or displacement test stainless materials (Except for HLW hot water heaters). ASME VIII, I, and IV refer to these as 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 yield stress to ultimate stress being below 0.625, again a description of stainless steel.
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) – 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) – When other codes do not tell how many tests are required for different sized parts that are otherwise similar, this passage from VIII-1 is often used. This is usually more restrictive than the more common practice of bursting a smallest, largest and one in the middle.
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 Material Test Report). This sometimes leads to registration issues.
Elevated Temperatures: UG-101(k) – If the operating temperature will be high enough that the part is no longer as strong as during the test, this section will correct for the difference.
Brittle Coat Testing: UG-101(l) – The first of many allowed test methods. Brittle coat testing is seldom used for VIII-1 applications. See caution 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 caution on stainless steel above.
Displacement Testing: UG-101(o) – Another more complex method with lower test pressures. Also not used very often. See caution on stainless steel above.
External Pressure: UG-101(p) – External pressure tests are run at 3x the external pressure, but a special test chamber is often required.
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 commonly see manufacturers running tests on every design or material variation.
Proof Test: HLW-502 – Section HLW has very 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. Stainless boiler parts must burst tested once to HG-502.3 and a second time by brittle coat test to this section if the part is to be used in both HLW and H stamp boilers.
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 the caution 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 this is often a way of describing stainless steel.
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) is often used for guidance.
A piping designer assumes a B16.9 fittings has the same strength as the equivalent schedule pipe. It is up to the manufacturer to prove that the fitting actually is this strong. They have the choice of proving this through calculations 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 of scaling of results from one material / size / thickness to other fittings compared with other ASME codes.
Burst Testing: 104.7.2(C) – Burst testing done to MSS SP-97, ASME B16.9, or ASME I A-22. ASME I A-22 is most commonly used.
Related Components: 104.7.2 – “It is permissible to interpolate between sizes, wall thicknesses and pressure classes and to determine analogies 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 useful size guidelines. Likewise, VIII-1 UG-101(d)(1) limits like materials to materials with the same P number.
Proof Testing: 304.7.2(c) – Proof testing can be done under ASME B16.9, MSS SP-97, ASME VIII-1. We prefer 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. To repeat, think beyond the first registration, think of other provinces and re-registering in the future.
Alberta Rules (Added Oct 10 2014)
Alberta has released a useful document 00370159.DOC.1 “PROOF TESTING REQUIREMENTS” which we expect to reduce the variation in requirements between reviewers, and hopefully even between provinces. 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: 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.