Maximum pressure for pipeline pneumatic test

[franciscobruzone]

Hello,

I can't find an explantion for what the code ASME B31.8 states regarding the maximum pressure test prescribed in table 841.3.2-1.

In this table the code says that the minimum pressure at which the pipe must be tested is 1.25 x MOP and the maximum 1.25 x DP. The problem is that the MOP and the DP are the same according to the proyect basic design parameters which is covered by the code as well.

The whole point of pneumatically testing the pipeline is to increase the altimetric difference during the test and reduce the number of test segments. But with what the code says I can't keep the condition of MOP=DP and have at the same time a relatively high altimetric difference.

Furthermore in table 941.3.3-1 the maximum hoop stress premissible during air or gas test is stablished for location class 2,3 and 4 but not 1. This confuses me a lot since I cannot see why I would reduce my MOP to 50% of my SMYS in location class 3 according to this table.

Can anybody help me with this dilema.

Thank you all,

Francisco

 

[LittleInch]

First item is indeed an issue if your MOP = your DP. This essentially means a flat pipeline.

Given that MOP is supposed to allow for excursions and trips etc, and B31.8 does not allow any overpressure above Design Pressure, I would set your MOP to be say 5% lower than your DP. Then hopefully the density of air is not enough to make such a difference across your elevation.

MOP is in your hands to reduce more so than DP increasing.

Table 841.3.-1 is only referenced in section 841.3.3 but confusingly is then listed after 841.3.4. 841.3.3 refers only to test of pipe with yield stress < 30% SMYS, but pressures > 100psig.

Ignore it and concentrate on table 841.3.2-1

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