Pressure values for the sensitivity leak test

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ASME B31.3 refers to what we commonly call hydrostatic testing, pneumatic testing, sensitivity leakage testing, airtightness testing, etc., all of which are termed LEAK TESTING, which translates to “leakage test”. However, this is not exactly the same as what is commonly referred to as a leak test in China. In China, the term “LEAK TESTING” as defined in ASME B31.3 is replaced by “pressure test”; meanwhile, “leak test” specifically refers to “airtightness testing” and “sensitivity leak testing”. Today’s focus isn’t on this; it’s just being brought up. 1 Regarding the selection of pressure values for the sensitivity leak test (detection), I previously compared the descriptions in multiple versions of ASME B31.3 (Para. 345.8.2). I found that they were all consistent with one another. Although I didn’t fully understand those descriptions, they utilized terms such as “at least”, “the lesser”, and “or”, which made them rather confusing. The provisions of ASME B31.3 Paragraph 345.8.2 are as follows: … When the Bubble Test – Direct Pressure Technique is used, (a) the test pressure shall be at least the lesser of 105 kPa (15 psi) or 25% of the design pressure. (b) The pressure shall be gradually increased until a gauge pressure equal to the lesser of half of the test pressure or 170 kPa (25 psi) is attained; at that point, a preliminary check shall be carried out. Then the pressure shall be gradually increased in steps until the test pressure is reached, with the pressure being held for enough time at each step to allow the stresses in the piping to equilibrate. Regarding clause (a), the translation provided by a translation software is: (a) The test pressure shall be at least the smaller of 105 kPa (15 psi) or 25% of the design pressure. According to GB/T20801.5-2020, the test pressure for (sensitivity leakage tests) \"shall be not less than 105 KPa or 25% of the design pressure, whichever is lower.\" The relevant description in Clause 9.3.6 of SH/T3501-2021 (Code for Construction and Acceptance of Steel Piping Systems for Toxic and Flammable Media in Petrochemical Industry) is: The “test pressure for the sensitivity leak test shall be no less than the lesser value between 105 kPa and 25% of the design pressure.” Due to the ambiguity of ASME B31.3 provisions, “or” and “and” were used in the translation; it seems that there is no difference, as both convey the same meaning. Therefore, there are two cases: 1) When the design pressure of the pipeline P > 0.4 MPa, the value of 25% of P is defined as P1. Since P1 > 0.1 MPa, the smaller value between P1 and 0.1 MPa is 0.1 MPa. Thus, the pressure for the sensitivity leak test (let Pt denote this test pressure) must be Pt ≥ 0.1 MPa. 2) When the design pressure P ≤ 0.4 MPa, the value of 25% of P is defined as P1; P1 ≤ 0.1 MPa. The smaller value between P1 and 0.1 MPa is taken as P1 (P1 ≤ 0.1 MPa). However, due to the “at least” requirement, the value Pt = 0.1 MPa is used as the pressure value for the sensitivity leak test. Comparing 1) and 2), it can be seen that in any case, 0.1 MPa can be chosen as the pressure Pt for the sensitivity leak test. Of course, when P > 0.4 MPa, any value of Pt greater than 0.1 MPa may also be used; however, this value should not exceed 25% of P. Article (b) states that the pressure should be increased step by step to the lower of 0.5 Pt or 170 KPa (0.17 MPa). From this, it can be seen that at this point, it falls under the condition where P > 0.4 MPa. Chapter 10 of Volume V of the ASME BPVC pertains to leak testing. Section T-1044 therein sets limits on pressure; it stipulates that unless specified in a mandatory appendix or in other volumes of this Code, pressure leak tests shall not be conducted at pressures exceeding 25% of the design pressure. T-1044 PRESSURE/VACUUM (PRESSURE LIMITS) Unless specified in the applicable Mandatory Appendix of this Article or by the referencing Code Section, components that are to be pressure-leak tested shall not be tested at a pressure exceeding 25% of the Design Pressure. 3(a) The test pressure shall be at least the lesser of 105 kPa (15 psi) or 25% of the Design Pressure. Given the doubts I had regarding the translation of the provisions in ASME B31.3 as mentioned in point 1, as well as the requirement in Section 10, T-1044 of ASME BPVC-V Volume 2 that Pt ≤ 25%P, I have reached the following understanding regarding the translation of ASME B31.3: namely, the test pressure Pt should be a value ≥ 0.1 MPa, with an upper limit of 25%P; in other words, 0.1 MPa ≤ Pt ≤ 25%P. Some people are concerned about the reliability of leak detection results at low pressures. In ASME B31.3 Interpretation 17-02, it is asked whether the pressure for the sensitivity leak test must be greater than 15 Psi (0.1 MPa) The reply is: No. This means it can be 0.1 MPa. Of course, the question also implies that Pt can also be greater than 0.1 MPa. However, it should be noted that the GB/T 20801.1-2020 standard explicitly states that it does not apply to pipes with a pressure rating above PN420, etc. Therefore, the relevant requirements for Class K pipes under ASME B31.3 may not necessarily conform to the provisions in the relevant volumes of GB/T 20801-2020. For example, regarding the leak testing of Class K (high-pressure) pipes as specified in ASME B31.3, there are relevant requirements in Section K345: K345.1(a) stipulates that a hydrostatic test or pneumatic test must be conducted on each weld and each component (except for fasteners, gaskets, and pressure relief devices used during operation). Otherwise, as required by K345.1(b), the installed piping system (excluding pressure relief devices used during operation) must be subjected to a leak test at a pressure not less than 110% of the design pressure to ensure its integrity. Note: This test is equivalent to the airtightness test mentioned in domestic standards (hereinafter referred to as the “airtightness test”, although the text does not explicitly state that the medium used in the test is gas). K345.1(d) stipulates that, with the owner’s approval, the pressure relief devices used during operation may be included in the airtightness test. In such cases, the test pressure may be reduced to prevent the operation or damage of these devices; however, it must not be lower than 90% of the minimum set pressure of the pressure relief devices in the system. K345.1(e) requires that, for the leak test of the final weld (sealing weld), a tightness test with a leak detection device may be used as an alternative to a hydrostatic test or pneumatic test. K345.1(f) requires that the following three leak tests shall not replace hydrostatic testing or pneumatic testing: (1) the initial operating pressure test, namely ASME B31.3 Para.345.7 or GB/T20801.5-2020’s 9.1.6. (2) The sensitivity leak test is equivalent to Para. 345.8 of ASME B31.3 or 9.2.1 of GB/T 20801.5-2020. (3) The substitute leak test is equivalent to Para. 345.9 of ASME B31.3 or 9.1.7 of GB/T 20801.5-2020. In other words, 1) for Class K pipelines, a sensitivity leak test cannot replace the pressure test (hydraulic or pneumatic) that is required; of course, exemption from the initial operation pressure test or from any pressure test is also not allowed. 2) For Class K pipelines, a gas tightness test is also required. When no safety valve is present during operation, the test pressure must be ≥110% of P (assuming P is the design pressure). When a safety valve is installed, the test pressure must be ≥90% of P.