Pressure Testing It is common practice to pressure-test a pipe system prior to placing it in service. Tests may be conducted using hydrostatic or pneumatic pressure. However, the Plastics Pipe Institute does not recommend pneumatic pressure testing of an above-ground installation, for which the test should be conducted hydrostatically, using a non-hazardous liquid such as water. Safety is of paramount importance when conducting pressurized internal fluid (liquid or gas) leak tests. Liquids such as water are preferred as test fluids because less energy is released if the test section fails catastrophically. Leak tests of pressure systems generally involve filling the system or a section of the system with a liquid or gaseous fluid and applying internal pressure to determine resistance to leakage. Leak tests of non-pressure systems typically involve testing sections of the system or individual joints using end plugs or bulkheads to determine resistance to leakage. Hydrostatic pressure leak tests of PE pressure piping systems should be conducted in accordance with ASTM International F 2164, Standard Practice for Field Leak Testing of Polyethylene (PE) Pressure Piping Systems Using Hydrostatic Pressure. The preferred hydrostatic testing liquid is clean water. Other non-hazardous liquids may be acceptable. Pneumatic testing should not be considered unless the piping system is so designed that it cannot be filled with a liquid; or the piping system service cannot tolerate traces of a liquid testing medium. If it is determined that pneumatic testing is applicable, the pressurizing gas should be non-flammable and non-toxic. As a general rule, pneumatic (compressed gas) pressure system leak testing should be approved in advance by the Owner and the responsible Project Engineer.