Hydrotest on Offshore Pipeline
Wednesday, February 17, 2016
The hydrotests are conducted mainly to verify the mechanical strength of pipeline or pipeline sections. Hydrotesting is carried out by pressurizing the system to a specified internal pressure and holding it for a certain period of time to check whether or not there is a pressure drop. If the pressure drops within the hold period, it is assumed that a leak or leaks may exist somewhere in the system. After the holding period is over, the pressure is released and a complete visual inspection follows. Standard codes, such as ASME B31.4, ASME B31.8, and API RP 1111, provide guidance on how to perform pressure tests of gas and liquid pipelines.
Hydrotest use water as fluid with
pressure larger than the design pressure. The test pressure is recommended to
be set at no less than 1.25 times the internal design pressure for both
hydrostatic testing and leak testing. The holding time is recommended to be at
least 4 hours for hydrostatic testing and at least 1 hour for leak testing.
A complete description of the
test equipment and instruments is very important for the success of the tests.
The following is a partial list of the devices needed for the tests:
- A high-volume pump that can fill the line at high enough velocity to remove debris and to push the pigs
- A filter that would remove all particles larger than a certain size to ensure the test fluid is clean
- A meter to measure the quantity of water filled
- Injection pumps for chemical injections
- A variable speed, positive displacement pump to pressurize the line. The pump should have a known volume per stroke and should have a stroke counter
- A pressure recorder that would continuously record the test pressure for the whole test period. The pressure measuring equipment should have an accuracy and repeatability of +-0.1%
- A temperature measurement device that is properly calibrated and should continuously measure the fluid temperature. The device should be able to read in increments of no less than 0.18F (0.058C)
- A temperature device to measure the ambient temperature
- Pressure relief valves
- Pig transmitter device or remote pig signaling system
How the test results will be
reported and what will be reported should be defined before performing the
tests. The test records should include the details of the test operations and
details of any failures. The failure report should include the exact location
of each failure, the type of failure, the causes for the failure, and the
recommended repair methods. When the tests are finished, all waste should be
disposed of in the correct manner which should be defined in the company’s
waste management and disposal policy.
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Source:
Guo, Boyun, Shanhong Song, Jacob Chacko, Ali Ghalambor. USA. 2005.
Bai, Yong and Bai, Qiang. Subsea Pipelines And Risers. USA: Elsevier Inc. 2005.
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