The Department of Transportation / Pipeline Hazardous Materials Safety Administration (PHMSA) issued a final rule that amends the design factor and design pressure limits for natural gas pipelines made from new Polyamide-11 (PA-11) thermoplastic pipe. These two changes in the regulations allow pipeline operators to operate certain pipelines constructed of new PA-11 pipe at higher operating pressures than is currently allowed for other plastic pipe materials. PHMSA published a Notice of Proposed Rulemaking (NPRM) (73 FR 1307; January 8, 2008) proposing to increase the design factor and corresponding operating pressure limitations for natural gas pipelines made from new PA-11 thermoplastic pipe. PHMSA is adopting the amendments as proposed in the NPRM with four exceptions:

• Adding the term "copper tubing size (CTS)" to clarify that pipeline operators may use copper tube size pipe as well as iron pipe size pipe. IPS means Iron Pipe Size, while CTS means copper tube size. These are recognized pipe size standards that refer to a nominal pipe diameter, not to the actual inside diameter (ID) or outside diameter (OD) of a pipe. IPS is generally used for pipe sizes 2 inches or greater; CTS is generally used for pipe sizes 2 inches or less.
• Adding the term "thicker pipe wall" to clarify that "SDR-11 or greater" means pipe with thicker pipe wall.
• Clarifying that the use of arithmetic interpolation to determine a design pressure rating at a specified temperature (i.e., "S" in the plastic pipe design formula in § 192.121) will not be allowed for PA-11 pipe.
• Not requiring that pipe with design pressures above 100 psig (689 kPa) be buried with a warning tape or other device designed to warn an excavator of the presence of a high pressure gas line.

The final rule amends the existing plastic pipe design formula in § 192.121 to cover pipelines made from new 4-inch IPS (or CTS) or less, SDR-11 or greater (i.e., thicker pipe wall) PA-11 pipe with a design factor of up to 0.40 and increases the design pressure limitation in § 192.123 to 200 psig (1379 kPa) for these same pipelines. The design factor for all other plastic pipes remains as prescribed in the existing regulations.

These rule changes are effective January 23, 2009.

For a copy of the Final Rule: Polyamide-11 (PA-11) Plastic Pipe Design Pressures, contact Jessica Roger.