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