PHMSA currently collects reports from pipeline operators by material categories.  These categories include cast/wrought iron, steel, and plastic. Cast or wrought iron pipelines were used from the early days of energy transportation through the 1940s.  These pipelines are among the oldest energy pipelines constructed in the United States. Many of these pipelines still deliver natural gas to homes and businesses today. However, the degrading nature of iron alloys, the age of the pipelines, and pipe joints design have greatly increased the risk involved with continued use of such pipelines. Steel has been used extensively since the 1950s.  Uncoated steel pipelines are known as bare steel pipelines and while many of these pipelines have been taken out of service, some of these pipelines are still operating today. The age and lack of protective coating typically makes bare steel pipelines of higher risk as compared to some other pipelines.  Plastic pipelines for gas distribution became prevalent in the early 1970s.

In 2011, following major natural gas pipeline incidents, DOT and PHMSA issued a Call to Action to accelerate the repair, rehabilitation, and replacement of the highest-risk pipeline infrastructure. Among other factors, pipeline age and material are significant risk indicators. Pipelines constructed of cast and wrought iron, as well as bare steel, are among those that pose the highest-risk.  To illustrate the progress pipeline operators are making in the replacement of aging gas pipelines, PHMSA provides an annually-updated online inventory of high-risk pipeline infrastructure by state. Specifically, the dynamic inventory highlights efforts to replace iron and bare steel gas distribution pipelines and shows trends in pipeline miles by decade of installation.  PHMSA has also seen evidence that other pipeline materials pose risks.  In 1999, PHMSA issued two advisory bulletins (ADB-99-01 and ADB-99-02) about brittle failures of plastic pipes manufactured in the early 1970s.  Modern plastic pipe is manufactured to resist brittle failures. 

On May 21, 2015, PHMSA published in the Federal Register a Notice of Proposed Rulemaking (NPRM) to amend the natural and other gas pipeline safety regulations (49 CFR Part 192) to address regulatory requirements involving plastic piping systems used in gas services.  These proposed amendments are intended to correct errors, address inconsistencies, and respond to petitions for rulemaking.  The requirements in several subject matter areas are affected, including incorporation of tracking and traceability provisions; design factor for polyethylene (PE) pipe; more stringent mechanical fitting requirements; updated and additional regulations for risers; expanded use of Polyamide-11 (PA-11) thermoplastic pipe; incorporation of newer Polyamide-12 (PA-12) thermoplastic pipe; and incorporation of updated and additional standards for fittings.  Click here for more information on the NPRM.