elylrc
Mechanical
- Oct 7, 2010
- 20
I am going to hot tap into a gas pipeline. What codes govern the hydrotest pressure required? The following is what I have read and does not appear to provide an answer.
1. ASME B31.8 is quite clear about hydrotesting new pipelines and re-hydrotesting existing pipelines to operate at a higher MAOP. In this case for zone 3, 1.4 times 1036 psig MAOP) = 1450 psig. However, apart from a definition, the only mention of hot taps for steel pipelines is as follows in section 841.2.6 Hot Taps. "All hot taps shall be installed by trained and experienced crews."
So I assume that B31.8 intends that hot taps be hydrotested to the criteria it sets forth.
2. API RP 2201 is a recommended practice for safe hot tapping practices and not a code for hot tap design. So I don't believe that Section 10.5 was written with anything in mind other than how to perform a pressure test with the hot tap machine installed to ensure a safe hot tap operation.
3. API Std 510, referred to in RP 2201 is a pressure vessel inspection code and is not relevant to piping systems and states this quite clearly:
"APPENDIX A—ASME CODE EXEMPTIONS
b. All classes of containers listed for exemption from the scope of ASME Section VIII: Division 1:
5. Piping components such as pipe, flanges, bolting, gaskets, valves, expansion joints, fittings, and the pressure-containing
parts of other components such as strainers and devices which serve such purposes as mixing, separating, snubbing, distributing,
and metering or controlling flow as long as the pressure-containing parts of these components are generally recognized as
piping components or accessories."
So the question becomes, is how does one satisfy ASME B31.8 ? It does not appear that one can in this situation. At least not based on API 1111, Section 4.3.2.1 Collapse Due to External Pressure. Assuming that the end of the existing pipeline was shut-in, the pressure would eventually rise to MAOP when the upstream control valves would close. With this internal pressure, API 1111, Section 4.3.2.1 calculates the external collapse pressure would be lower than the required B31.8 test pressure.
1. ASME B31.8 is quite clear about hydrotesting new pipelines and re-hydrotesting existing pipelines to operate at a higher MAOP. In this case for zone 3, 1.4 times 1036 psig MAOP) = 1450 psig. However, apart from a definition, the only mention of hot taps for steel pipelines is as follows in section 841.2.6 Hot Taps. "All hot taps shall be installed by trained and experienced crews."
So I assume that B31.8 intends that hot taps be hydrotested to the criteria it sets forth.
2. API RP 2201 is a recommended practice for safe hot tapping practices and not a code for hot tap design. So I don't believe that Section 10.5 was written with anything in mind other than how to perform a pressure test with the hot tap machine installed to ensure a safe hot tap operation.
3. API Std 510, referred to in RP 2201 is a pressure vessel inspection code and is not relevant to piping systems and states this quite clearly:
"APPENDIX A—ASME CODE EXEMPTIONS
b. All classes of containers listed for exemption from the scope of ASME Section VIII: Division 1:
5. Piping components such as pipe, flanges, bolting, gaskets, valves, expansion joints, fittings, and the pressure-containing
parts of other components such as strainers and devices which serve such purposes as mixing, separating, snubbing, distributing,
and metering or controlling flow as long as the pressure-containing parts of these components are generally recognized as
piping components or accessories."
So the question becomes, is how does one satisfy ASME B31.8 ? It does not appear that one can in this situation. At least not based on API 1111, Section 4.3.2.1 Collapse Due to External Pressure. Assuming that the end of the existing pipeline was shut-in, the pressure would eventually rise to MAOP when the upstream control valves would close. With this internal pressure, API 1111, Section 4.3.2.1 calculates the external collapse pressure would be lower than the required B31.8 test pressure.
