Burst Testing at PVEng
Pressure Vessel Engineering regularly provides burst testing services to prove products for CRN registration. We have years of experience using burst testing to register products and have the knowledge to get the job done right and as economical as possible.
Benefits of using PVEng:
- 10+ years of successful experience
- Extensive knowledge of registration requirements
- Fast professional service
For projects with several components we can identify the minimum amount of testing required and provide more economical approaches when appropriate. We also provide Finite Element Analysis for components which are not appropriate for destructive testing.
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General Burst Test Requirements
The maximum allowable working pressure for vessels or vessel parts for which the strength cannot be computed with satisfactory assurance of accuracy can be established by burst testing in accordance with ASME VIII-1 UG-101(a)(1), or through Finite Element Analysis (FEA) in accordance with ASME VIII-2.
Burst testing and FEA may only be used for the purpose of establishing a maximum allowable working pressure of those elements or components for which code calculations cannot be applied. Code calculations must be completed for all elements or components which they may be applied as per ASME VIII-1 UG-101(b).
Burst testing is usually limited to “fittings”; generally a component can be classified as a fitting providing its volume is < 1.5 cu.ft. FEA is typically used for components larger than this, or where it is not economical to complete destructive testing.
In Canada fittings fall into the following categories (CSA B51-14,Table 1):
- A: Pipe fittings, including couplings, tees, elbows, wyes, plugs, unions, pipe caps, reducers
- B: All flanges
- C: All line valves
- D: All types of expansion joints, flexible connections, hose assemblies
- E: Strainers, filters, separators, steam traps
- F: Measuring devices, pressure gauges, level gauges, sight glasses, levels, pressure transmitters
- G: Certified capacity-rated pressure-relief devices acceptable as primary overpressure protection on boilers, pressure vessels and pressure piping, fusible plugs
- H: Pressure retaining components that do not fall into above categories
Fittings can be “grouped” into the above categories and registered as a catalog to reduce registration costs. *Saskatchewan does not require category A, B, C and G fittings to be registered. British Columbia does not require registration of all Category A, B, C and G fittings.
Determining the MAWP (maximum allowable working pressure)
The MAWP for ductile metals is typically 20 – 25% of the proof test pressure, calculated in accordance with ASME VIII-1 UG-101(m).
(1) P = (B / 4) X ((Su * E) / (Suavg)) (2) P = (B / 4) X ((Su * E) / (Sur)) Where B = Burst test pressure, or pressure at which test was stopped E = Efficiency of welded joint as per ASME VIII-1 UW-12 (if applicable) F = Casting quality factor as per ASME VIII-1 UG-24 (if applicable) Su - Specified minimum tensile strength at test temperature Suavg = Average tensile strength at test temperature Sur = Maximum tensile strength at test temperature
When using eq (1) above some provinces require a minimum of (3) tensile test to be completed to determine Suavg. Using eq (2) eliminates this requirement; however few material specifications provided a maximum tensile value, in which case this equation may not be used.
The resulting MAWP must then be reduced by the elevated temperature reduction, corrosion reduction and casting efficiency if applicable:
Elevated temperature reduction as per ASME UG-101(k)
(3) MAWP = P * (S / S2) Where S = Maximum allowable material stress at design temperature S2 = Maximum allowable material stress at test temperature (Values S & S2 are listed at ASME IID Table 1A & 1B)
For unlisted materials similar material allowable stresses from ASME IID may be used providing similarity is justified. Proof testing may also be completed at the elevated temperature, or tensile tests performed at elevated temperature to determine material strength reduction.
Corrosion reduction as per ASME VIII-1 UG-101(i)
(4) MAWP = P * ((t - c)n / t n)
c = corrosion allowance
n = 1 for curved surfaces, 2 for flat surfaces
t = nominal thickness of material at the weakest point
Casting efficiency as per applicable code, i.e. ASME VIII-1 UG-24, ASME B31.3 Table A-1A
Brittle fracture failure must also be addressed if the component is subject to operation temperature lower than proof test temperatures. Minimum temperature values are provided for ASME / ANSI listed materials in some ASME codes i.e. ASME IID, ASME B31.3. If materials are unlisted documentation must be provided to identify the brittle fracture transition temperature. If documentation is not available impact testing or a low temperature proof test may be required.
For materials other than ductile metals TSSA provides the following guidelines for minimum proof test pressure:
- Flexible hose assemblies 4X
- Rubber expansion joints 4X
- Cast Iron 6X
- Glass 10X
- Non-metallic, non-automated fabrication process 10X
The above values must also be increased to account for temperature, corrosion, and casting efficiencies as listed above. These are TSSA guidelines only; higher safety factors may be required for different provinces. It is suggested for this reason that all burst tests be taken to failure.
Finite Element Analysis (FEA) can be an economical alternative to burst testing or as a means to qualify components which would not otherwise meet the above safety factors.
Burst testing must be completed for each material of construction unless they can be grouped by the same p-number with similar properties.
The maximum allowable working pressure for geometrically similar parts may be established by a series of burst tests that uniformly cover the complete range of sizes. Interpolation between and an appropriate selection of intermediate sizes may be used to qualify all components of a range of sizes ASME VIII-1 UG-101(d)(2).
Canadian Registration Requirements
Documentation required for a CRN submission using burst testing as a qualifying means is listed below. These documents are required to be submitted to each province of registration.
Quality Control Certificate (Manufacturers – pick one of the following)
- ISO (with appropriate scope)
- ASME “U” stamp
- Others (suggested to be reviewed by Pressure Vessel Engineering)
Statutory Declaration (Manufacturers)
- Signed by a person of authority employed by the manufacturer
- Fitting marking identified (as per MSS SP-25)
- Required for each fitting category (if applicable)
Burst Test Report
- Witnessed and signed by an Authorized Inspector
- Design conditions
- Code of construction
- Maximum allowable working pressure
- Maximum temperature
- Minimum temperature
- Corrosion allowance
- Material(s) of construction
- Welding (if applicable)
Material specifications for non-code listed materials
- Mechanical properties
- Chemical properties
Burst Test Requirements
Burst testing must be completed in accordance with ASME VIII-1, UG-101. Burst testing must be witnessed and signed off by an authorized inspector. A burst test report must be completed containing, but not limited to:
- The test set-up
- Test gauge information
- Test procedure
- Authorized Inspector sign off and National Board number
This article was written using the following documents as references:
- CSA B51-09: Boiler, pressure vessel, and pressure piping code
- ASME VIII-1, 2007 ed: Boiler and Pressure Vessel Code
- TSSA: Guidelines for the registration of non-nuclear fittings in the province of Ontario
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-188.8.131.52 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.
Common Problems Using Burst Testing
PVEng has registered hundreds of fittings using burst testing. Based on our own experience and reports from our customers, these are the most common burst test fitting registration problems, starting with the most frequent:
1) Burst test pressure is not correct (4.5x factor used).
Many applicants have been told by a jurisdiction that they can register fittings by burst testing the parts to a 4.5x factor of safety*. Typically they are told this by phone, occasionally by email, it does not matter which. The problem starts after the burst test is complete and the fitting is being registered. Three problems can occur. i) the fitting goes to a different reviewer at the same jurisdiction who does not agree with using the 4.5x factor – the job is rejected*; ii) the registration is accepted by the first jurisdiction but rejected by another jurisdiction; or iii) The job gets registered across Canada, but as the CRN expires at the 10 year anniversary, the original burst test results are not accepted for renewal and new tests are required.
Fitting burst tests are most commonly done to the requirements of VIII-1 UG-101(m). The required test pressure is dependent on the strength of the part vs the specified minimum material strength. Additional correction factors based on operating pressure, weld or casting efficiencies, and corrosion allowances all increase the required burst pressures. It is not uncommon to require a burst test pressure 6-7x operating to meet all of the requirements of UG-101(m).
Although a burst test does not have to be taken to destruction, we recommend that the pressure be taken as high as possible to allow for all of the correction factors required. Proper safety precautions are mandatory during burst tests as large amounts of stored energy are possible, even when tested using liquids.
We have found no written guidelines that allow the 4.5x factor of safety to be used. For further information see “Registration of Plastic Fittings“.
* We at PVEng agree that a fitting is safe after being tested to 4.5x operating pressure for most service conditions; however the problem is in getting the results accepted by all review engineers.
** In one jurisdiction about 75% of the reviewers will accept the 4.5x “rule”, in another about 50%. If you use this rule, it is critical that the job goes back to the reviewer that advised you to use it. Do not expect it to be accepted Canada wide.
2) Not enough pull tests have been performed on the parts.
See UG-101(j)(2) for the rules covering the yield/tensile test coupons. Three to four test specimens are supposed to be taken from an un-yielded location of the part that has been tested. This can be difficult for small fittings, and then the tests have to be taken from another part from the same heat batch.
VIII-1 UG-101(j)(2): Yield or tensile strength so determined shall be the average from three or four specimens cut from the part tested after the test is completed. The specimens shall be cut from a location where the stress during the test has not exceeded the yield strength. The specimens shall not be flame cut because this might affect the strength of the material. If yield or tensile strength is not determined by test specimens from the pressure part tested, alternative methods are given in (l), (m), (n), and (o) below for evaluation of proof test results to establish the maximum allowable working pressure.
Some material specifications provide a maximum and minimum allowed tensile and yield range. These materials can be burst test with only 1 pull test. The trade-off is that the required burst test pressure based on the maximum strength is likely to be higher than if the three tests were taken and the results averaged.
Updated Oct 10 2014: See the above ABSA document which clarifies when more than one pull test sample is required and when the MTR can substitute.
3) The witnessing of burst test is not being accepted.
Companies not located in North America are sometimes using inspectors other than National Board certified Authorized Inspectors to witness burst tests. Although the inspectors being used are qualified for the job, at least one jurisdiction will reject burst tests not witnessed by an Authorized Inspector as defined in UG-91:
All Inspectors shall have been qualified by a written examination under the rules of any state of the United States or province of Canada which has adopted the Code.
The inspectors that meet this requirement are National Board certified. Make sure they put their National Board serial number after their signature on the burst test report.
4) Using burst tests to prove parts that could also be proven by code calculations
Proof tests are not allowed to be used to replace code rules – see UG-101(b). You might need the proof test to show the strength of part of your fitting, but if other portions can be calculated to code, then they must be. The proof test cannot be used to provide a higher operating pressure for those parts that can be calculated.
5) Not enough tests have been done to prove a complete range of parts
Typically to prove a range of parts for CRN registration by code calculations the smallest, largest and a size at mid-range are analyzed and the results are interpolated for the other sizes. Detailed geometric information is required to prove that the calculations are accurate or conservative for all the sizes not computed. This also applies if burst testing is used to justify fittings, however UG-101(d)(2) requires that 5 burst tests be done covering the range. Most reviewers will accept 3 tests to cover a range but we know of at least one that will always insist on 5 tests.
6) Burst tests used to justify materials not tested
UG-101(d)(2) specifies when one material can be used to justify another based on similarities like greater tensile strength + equal P number + same or tougher material grouping – read carefully. Typically if a product is available in multiple materials, then multiple burst tests will be required. Although it is possible to use code calculations of weak materials to prove the strength of otherwise identical fittings made from stronger materials, this is not allowed in burst testing.
Alternatives to Burst Testing – the requirements of 6 and 7 above can make it more economical to use methods such as finite element analysis instead of burst testing, even on small parts.
7) Lastly, the report is occasionally a problem.
VIII-1 UG-101(b) specifies that the report:
VIII-1 UG-101(b): The report shall include sufficient detail to describe the test, the instrumentation and the methods of calibration used, and the results obtained.
Also refer to the Alberta requirements listed above.
It is our experience that the variations found in the requirements for burst testing vary greatly between review engineers, but the new Alberta guidelines should help. As always, try to get your advice in writing, and try to get your project reviewed by the same reviewer providing the advice. Regardless of any advice that you get, the closer you stick to the requirements of bust testing as outlined by VIII-1 UG-101, the less trouble you will have now or in 10 years when it is time for renewals.