Pressure testing of in-service welded fittings

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Question:

Section 16.14 of both the 2016 and 2020 versions of AS/NZS 2885.2 specifies the pressure used to leak test an in-service welded fitting. However the wording changed from "... not greater than the current internal pressure of the pipeline” to "... at least the current internal pressure of the pipeline”. What was the thinking behind this change? Would the standard 1.25 x MAOP be a sensible test limit in line with the rest of the AS/NZS 2885 series?

Answer:

Some pipelines operate at a pressure well below the MAOP, so the 2016 version wording could result in low test pressures. The minimum test pressure is specified as the internal pressure in the pipe at the time of the test, and the effect of pipeline buckling due to the external test pressure needs to be considered for any test pressures exceeding the internal pressure in the pipe at the time of the test. The test should be performed at the highest pressure possible, but not exceeding 1.25 X MAOP or the pressure that would cause external buckling of the pipeline.