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.
An initial service leak test may be acceptable when other types of tests are not practical, or where leak tightness can be demonstrated by normal service, including when initial service tests of other equipment are performed. Test equipment and the pipeline should be examined before pressure is applied to ensure that connections are tight, necessary restraints are in place and secure, and components that should be isolated or disconnected are isolated or disconnected. All low pressure filling lines and other items not subject to the test pressure should be disconnected or isolated.
During all pressure system tests, the pipeline section to be tested must be restrained against movement in the event of catastrophic failure. Joints may be exposed for leakage examination provided that restraint is maintained.
Some systems may not be suitable for pressure leak testing. These systems may contain non-isolatable components, or temporary closures may not be practical. Such systems should be carefully inspected during and after installation. Inspections such as visual examination of joint appearance, mechanical checks of bolt or joint tightness, and other relevant examinations should be performed.
Testing of non-pressure systems such as sewer lines should be conducted in accordance with ASTM International F 1417, Standard Test Method for Installation Acceptance of Plastic Gravity Sewer Lines Using Low Pressure Air.
Additional information on pressure testing of installed PE pipe systems is provided in Chapter 2 of the Plastic Pipe Institute (PPI) Handbook of Polyethylene Pipe, which is available at www.plasticpipe.org/pdf/chapter02.pdf