The Department of Transportation Pipeline and Hazardous Materials Safety Administration (DOT / PHMSA) issued an update to information provided in Advisory Bulletin ADB–86–02 advising owners and operators of gas pipelines to consider the potential failure modes for mechanical couplings used for joining and pressure sealing two pipes together. Failures can occur when there is inadequate restraint for the potential stresses on the two pipes, when the couplings are incorrectly installed or supported, or when the coupling components such as elastomers degrade over time. In addition, inadequate leak surveys which fail to identify leaks requiring immediate repair can lead to more serious incidents. PHMSA advises operators of gas distribution pipelines using mechanical couplings to do the following to ensure compliance with 49 CFR 192:
- Review procedures for using mechanical couplings, including the coupling design and installation and ensure that they meet manufacturer’s recommendations;
- Review leak survey procedures to ensure that leak surveys are properly conducted, taking into account other contributing factors (i.e., weather conditions, calibration); and,
- Review personnel qualifications to ensure they address leak surveys sufficiently.
PHMSA also advises operators of gas distribution pipelines using mechanical couplings to consider taking the following measures to reduce the risk of failures of mechanical couplings:
- Use Category 1 fittings only if mechanical couplings are used on pipe sizes 1/2′ CTS (Copper Tube Size) to 2′ IPS (Iron Pipe Size). Per ASTM D2513-99 titled “Standard Specification for Thermoplastic Gas Pressure Pipe, Tubing and Fittings,” Category 1 is a mechanical joint design that provides a seal plus a resistance to a force on the pipe end equal to or greater than that which will cause a permanent deformation of the pipe. At this time there is insufficient data to indicate there are issues involving fittings for larger diameter pipe. PHMSA will revisit if such issues do arise with larger diameter pipe.
- Improve recordkeeping on specific couplings that exist, i.e., their type, installation date, maintenance schedule, and any failures encountered, to help identify a trend of problems that may occur with a specific coupling or type of installation.
- Consider whether to adopt a full replacement program if there are too many unknowns related to couplings in service.
- Work with Federal and State pipeline safety representatives, manufacturers, and industry partners to determine how best to resolve potential issues in their respective state or region.
For a complete copy of the updated advisory, or for more information, contact Jessica Roger