System pressure test for offshore pipelines - Are there alternatives?
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An important part of the pre-commissioning tasks is the system pressure test. The background for performing this final test is to confirm the leak tightness and to some degree the strength of the whole system and ensure that it is without any gross errors and defects. In some cases filling the pipeline with water in order to pressure test it is quite cumbersome and associated with some challenges and even additional threats to the pipeline integrity, i.e. the benefits with the test is lower than the advantages. For this reason the DNV-OS-F101 contains a clause opening for replacing the system pressure test by alternative means to ensure the same level of integrity. The system pressure test was developed in the 1950’ies as a way to avoid a lot of the failures experienced when pipeline were set into operation. By pressure testing the system after all installation and construction works were finalised, any gross defects were revealed and could be fixed before the pipeline was filled with hydrocarbons. As such this test proved to be a very useful test. However, due to developments in pipe materials, pipe manufacturing, welding, NDT, installation methods and QA/QC it is questioned whether the test is still relevant or could be avoided. This presentation is trying to summarise the background for the system pressure test, trends in defects discovered by the test and the current status. It further look into the requirements in DNV-OS-F101 in case one consider replacing the system pressure test by alternative means and give a few example of projects where this has been done where the benefits and disadvantages are briefly discussed.
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