Hydrostatic Test Planning

If your company is planning to conduct a hydrostatic test of a new or an existing pipeline, we may be able to help you get the most effective test. We can help you select the most appropriate test pressure. For new pipelines, the test pressure should be as high as feasible without causing excessive amounts of yielding. Usually this involves testing to 100 percent of SMYS or more and monitoring by means of a pressure-volume plot. Things to consider are the distribution of pipe yield strengths based on pipe mill data, pressure-volume plotting, and acceptable limits on strain, elevation differences and test section lengths, and the impact of the test on pipe-manufacturing imperfections that are too small to be revealed by the test. We can assist in these matters. Based on the anticipated service and operating conditions, we may also be able to establish service-life projections for the various choices of pressure levels.

When it comes to testing or retesting existing pipelines, the issues may differ from those associated with testing a new pipeline. For example, why is the test being conducted? How long can the pipeline be out of service? As in the test of a new pipeline, the objective is to get the highest possible test-pressure-to-operating-pressure level. But, considerations such as the anticipated number of test breaks, the types of defects expected, and the limits on downtime may force compromises. What we do is to look at the benefits of the test in terms of demonstrating a suitable remaining service life. Whether or not the test can be carried out to levels of 90 to 95 percent of SMYS or to higher levels depends on what types of defects are present and how large they are. It is important to eliminate defects that have grown by pressure-cycle-induced fatigue, but it is not necessarily productive to cause failures of original manufacturing defects. Planning for such a test should involve a review of the pipeline's operating and service-failure history. Also, if available, the pipe manufacturer's data should be reviewed. We can help on these issues. We can suggest ways to minimize test breaks and downtime. We can also calculate remaining service lives after the test based on alternative tests.

In any test, be it of a new or an existing pipeline, it is important to examine any test failures to determine their causes. We are equipped to do this. Our report will show the causes and discuss the implications for the serviceability of the pipeline after the test.