Underground Hydro Test

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ASME B31.3 requires this testing to ensure tightness and strength. ASME B31.3 section 345

Buried high pressure oil and gas pipelines are tested for strength by pressurizing them to at least 125% of their maximum operating pressure (MAOP) at any point along their length. Since many long distance transmission pipelines are designed to have a steel hoop stress of 80% of specified minimum yield (SMYS) at MAOP,

this means that the steel is stressed to SMYS and above during the testing, and test sections must be selected to ensure that excessive plastic deformation does not occur.

Your stroke counter will give you a exact figure if the deformation in volume, one the stroke volume is known and the size of the pipeline.

The volume will increase by overstressing - your pressure goes down due to this event and the count of strokes times the volume per stroke (of your pump) is the expansion.

Test pressures need not exceed a value that would produce a stress higher than yield stress at test temperature. ASME B31.3 section 345.4.2 (c)

Other codes require a more onerous approach. BS PD 8010-2 requires testing to 150% of the design pressure - which should not be less than the MAOP plus surge and other incidental effects that will occur during normal operation.

Leak testing is performed by balancing changes in the measured pressure in the test section against the theoretical pressure changes calculated from changes in the measured temperature of the test section.

The exact procedures to follow are described in the codes. (see internet) This is a very good one:

Australian standard AS2885.5 "Pipelines—Gas and liquid petroleum: Part 5: Field pressure testing" gives an excellent explanation of the factors involved.