Comparative Risks of Static Tests for Pipelines

This online engineering PDH course presents the processes associated with a pipeline static strength test and discusses the risks associated with both hydrostatic tests and pneumatic tests.

When a pipeline, gathering line, or well flow line is constructed, an important step in the process is to verify that the line is fit for its purpose using some form of non-destructive testing. Many projects employ x-ray or magnetic particle testing during construction to confirm that welds meet design conditions. Virtually all projects include an after-construction strength test in addition to any other non-destructive tests. These strength tests are intended to ensure that the line can be safely operated at pressures approaching the Maximum Allowable Working Pressure. To conduct a strength test you fill the piping up with a test fluid, raise the pressure to some multiple of the MAWP, hold the pressure for a defined period, and depressurize/remove the test fluid.

The test fluid tends to be water or some available gas with a very strong bias in the industry towards water. This bias manifests itself in informal reluctance to consider another fluid; Company Policy prohibiting pneumatic tests; and even regulations putting rigid restrictions and very large exclusion zones around pneumatic tests.  This bias, like so many arbitrary exclusions, stems from an improper extrapolation of very good research.  This course discusses actual risks and tries to expose the source of bias in favor of hydrostatic tests.