Comparative Risks of Hydrostatic and Pneumatic Pipeline Testing

Abstract

An important step in a pipeline-construction project is confirming that the piping and facilities are adequate for the expected operating pressures via static strength tests. All fluids have mass and internal energy. Fluids under pressure have significantly elevated internal energy. All fluids are compressible to some greater or lesser extent, and the fluid added to raise the pressure of the fluid in the bulk volume adds significant energy. The raw mass of a fluid must be considered when evaluating terrain elements and support elements (i.e., pipe stands and pipe racks). The selection process for a test fluid should always endeavor to minimize the total risk of the entire process. Code-guidance has historically not shown a clear preference for the selection of one particular test medium over another. Some jurisdictions have written regulations that step away from ASME guidance and do show a clear preference for hydrostatic testing over pneumatic testing. This preference manifests itself in several ways, but the primary representation is the requirement in statutes and regulations that a pneumatic test should have an “exclusion zone” around the test to reduce the risk of injury during the test. These documents tend to not have an exclusion-zone requirement for hydrostatic tests. This paper is undertaken to demonstrate the relative risks of liquid versus gaseous test media and presents a background of why pneumatic tests have been singled out by regulators as higher risk and shows why this regulatory preference can result in increasing risk rather than decreasing it.