The Pipeline and Hazardous Materials Safety Administration (PHMSA) says pipelines can use new Polyamide 11 (PA 11) thermoplastic pipe at higher operating pressures than currently allowed starting on Jan.25, 2009, and without applying for waivers. In issuing the new rule, PHMSA said distribution and transmission pipelines which bury the plastic pipe do not have to attach warning tapes or other devices designed to alert excavators to the presence of a high pressure line. Some state regulators had pressed for the warning tape requirement.
PA 11 pipe is frequently used as a replacement for smaller diameter metal pipe because plastic avoids corrosion risk. States and PHMSA have allowed its use at higher operating pressures under a handful of waivers granted by PHMSA in the past few years. Those waivers were based on successful tests run by Nicor Gas in conjunction with the Gas Research Institute (GRI) and its successor, the Gas Technology Institute (GTI). Nicor got one of those waivers for use of PA 11 in Illinois (the Illinois Commerce Commission also approved that) with PHMSA and state agencies granting subsequent waivers to Atmos Energy, Nashville Gas, Questar Gas and the City of Mesa Gas Utilities, among others.
The PHMSA final rule issued in late December allows distribution and transmission pipelines to start using PA 11 of a .40 allowable design factor at operating pressure up to 200 psig (the current limit is 100 psig) if the minimum wall thickness is Standard Dimension Ratio 11 or thicker and the rapid crack propagation characteristics of each new pipe design are measured using accepted industry standard test methods.
PHMSA estimates that approximately 1,450 gas distribution systems operating 1.2 million miles of gas distribution mains and 1,450 gas transmission and gathering systems would be affected by the proposed rule. The latter have approximately 35,000 miles of pipeline in Class 3 locations and approximately 1,400 miles of pipeline in Class 4 locations.