5 - Hydrostatic Testing

Abstract

This chapter focuses on the various issues regarding the use of hydrostatic testing to verify pipeline integrity. In the case of a new pipeline constructed of modern high quality and high-toughness line pipe, the maximum test level can generally be in excess of 100% of SMYS. The average yield strength of an order of pipe is usually well above the minimum specified value and very few pieces will have yield strengths low enough to cause yielding at 100% of SMYS. Yielding does not hurt or damage sound pipe and does not damage the coating also. Very little pipe actually undergoes yielding in a test to 110% of SMYS and those joints that do yield do not affect pipeline integrity, where the amount of yielding is also small. The most important reason why a hydrostatic test may not be the best way to validate the integrity of an existing pipeline is that in-line inspection is often a better alternative. From the standpoint of other types of defects also, the appropriate in-line inspection technology is evolving rapidly and, in some cases, it has proven to be more effective than hydrostatic testing. There are still certain existing pipelines for which hydrostatic testing remains the best and, in some cases the only means to revalidate their serviceability. In those cases, the mill hydrostatic test level for the pipe should be determined . It is also a good idea to conduct an integrity test as a "spike" test, where the idea is to test to as high a pressure level as possible, but to hold it for only a short time. The spike test establishes the effective test-pressure-to-operating-pressure ratio apart from checking for leaks.