Case study: technical review of large scale commercial installations using polyamide 11 based high pressure natural gas piping system and durability testing

Since late 2008, through amendment to US DOT CFR Title-49, Part-192, plastic piping system made from Polyamide 11 (PA-11) is permitted by the USA Department of Transportation for use in natural gas distribution systems. While research, development, and application testing of PA-11 pipe and resin, as presented previously, has proven its reliability and safety, commercial installations have provided an opportunity to expand our understanding of this piping system and its applications. This paper will present an overview of the commercial field installations that have been completed since 2009. This will include the layout and operating pressures, the design and engineering aspects, installation techniques and cost analysis of the PA-11 piping system. The case study aims to summarize key learning from seven installations totaling close to 40 km of this new piping system that is in service today. These PA-11 piping systems were designed in a 4 inch IPS SDR 11 pipe suitable for operations up to 17bars, to replace ageing metallic gas mains. A 17km long main that connected two city gates was installed with open trench installation method, and some horizontal drilling application under highways and water bodies. Some service lines have been installed severing farm houses directly from these main lines. All these installations confirmed that PA-11 piping system can be installed using similar techniques and same tools as PE piping system, and can be safely operated at much higher pressures than Polyethylene (PE) solid wall piping systems. Cost analysis of these installations also confirmed that PA-11 piping system offers a significant cost savings over steel system on a total installed cost basis. The lifetime cost savings (Cost of Ownership) of PA-11 piping systems is an additional economic advantage with negligible maintenance cost when compared to steel piping systems.