Volume 8, Issue 8 (September 2011)
Polyamide 12 Natural Gas Distribution Systems Operating at Pressures Greater Than 125 Psig
As a result of the long history of use of polyethylene systems in natural gas distribution systems, the advantages of thermoplastic distribution systems over steel systems are clearly recognized. These advantages include both short-term economic benefits due to advantages in total installed costs and long-term life service benefits due to the excellent corrosion resistance of thermoplastic systems. Historically, a weak point of the thermoplastic systems currently in use commercially are limitations in use due to operating pressure and end use temperature constraints. Initiatives exist within the natural gas distribution sector to identify materials capable of offering the advantages of currently available thermoplastic systems while extending the operating pressure range and end use temperature. Polyamide 12 has been identified as one material capable of meeting these needs. In 2004, a project was initiated by UBE Industries, Ltd. to evaluate the feasibility for use of polyamide 12 in natural gas distribution systems in the United States. The objective of the project was to develop a polyamide 12 natural gas distribution system capable of operating at pressures greater than that imposed by current restrictions and at temperatures above those achieved by commercially available thermoplastic systems. U.S. regulatory restrictions limit the use of thermoplastic systems to a maximum operating pressure of 125 psig. As the project progressed, the scope was expanded to include global activities. The project was broken into two distinct phases. Phase 1, from February 2004 to December 2006, included a comprehensive laboratory evaluation and limited field service use to determine the feasibility for use of polyamide 12 natural gas distribution systems operating at pressures greater than 125 psig and elevated temperatures. Long-term strength performance, slow crack growth and rapid crack propagation characteristics, the effect of secondary stresses along with extensive testing to accepted industry test methods were evaluated. Studies were conducted to develop a full set of installation, maintenance, and operating procedures for the use of polyamide 12 systems. Additionally, several small scale private property installations took place as part of the phase 1 project. Based on the positive results from laboratory and field evaluations of polyamide 12 systems, a phase 2 project was developed. The objective of the phase 2 project was to commercialize the use of polyamide 12 systems for use at pressures greater than 125 psig. During this phase of the project, installations are being performed with utilities in North America within their respective operating areas. These installations are being performed under special permits in cooperation with the respective federal and state regulatory bodies. As a separate activity, samples have been removed from the trial installations at specific time intervals and characterized for retention of physical and mechanical properties. The sample removal and evaluation study is an ongoing activity. The results of the project demonstrate that polyamide 12 offers a viable, cost effective alternative to steel pipe for systems operating above the range of currently available thermoplastic systems capability. In terms of both pressure bearing capabilities and high temperature operating performance, polyamide 12 systems extend the range of use for thermoplastic systems in natural gas distribution applications. The paper presents an overview of the laboratory analysis and field installation activities performed in the polyamide 12 gas distribution systems project. The data are presented in the context of compliance to the active ASTM polyamide 12 standards.