A pneumatic pressure test can be performed when hydrotesting a pipe is infeasible and/or impracticable. Despite its use throughout the industry, little published reference material is available regarding this important and ubiquitous topic with no known industry codes, standards or criteria identified to provide guidance related to stabilization time, test evaluation, and acceptance criteria.
This paper provides an evaluation of minimum stabilization time for various pipe sizes and lengths obtained from transient, parametric simulation results. By evaluating typical test parameters, the paper concludes that gas mass should be used as the principal evaluation criterion, since it is conserved during testing if there is no leak. This paper introduces an acceptance index for which a test can be accepted provided the acceptance index is within defined lower and upper limits obtained from the accuracy of the pressure and temperature measuring devices.
Field test data from three cases studies are successfully presented to verify the feasibility and validity of the proposed acceptance criteria for natural gas mains pneumatically tested with nitrogen at test pressures in the range of 300 psig (2,068 kPag) to 900 psig (6,205 kPag).