PHMSA Issues Advisory Bulletin Regarding Mechanical Couplings Used in Natural Gas Distribution Systems

On March 4, the Department of Transportation’s Pipeline and Hazardous Material Safety Administration (PHMSA) issued an Advisory Bulletin urging operators of natural gas distribution systems to review their procedures for using mechanical couplings and ensure that design and installation procedures for couplings, leak survey procedures, and personnel qualifications meet federal pipeline safety requirements.  The Advisory Bulletin also urges operators to work with federal and state pipeline safety representatives, manufacturers, and industry partners to determine how best to resolve potential issues in their respective states or regions. 

Background:  Incidents Involving Mechanical Couplings

The PHMSA notice recounts that, in 1986, an Advisory Bulletin addressed pipeline failures attributable to temperature-related contraction of plastic pipe and inadequate restraint capabilities of mechanical couplings.  At that time, natural gas pipeline operators were advised to review procedures for using mechanical couplings to ensure that coupling designs, procedures, and personnel qualifications satisfied federal requirements.  In addition, a report by the National Transportation Safety Board issued at that time found that the cyclic effects associated with temperature-related contraction and expansion on plastic pipe in improperly designed mechanical joints can be cumulative and lead to failure even after several years of satisfactory service. 

Since the mid-1980’s, PHMSA has examined over 3,400 incident reports submitted by distribution companies and determined that some are attributable to failures of couplings or fittings.  While the percentage of these types of incidents is small as compared to all distribution incidents reported, the incidents were significant, resulting in property damage, injuries, and fatalities.  In addition, PHMSA believes that the number of coupling or fitting incidents could be much higher, as it did not examine incidents reported only to states.  Given the potential for future significant incidents, PHMSA has determined that increased attention should be given to mechanical couplings.       

PHMSA explained that while a number of variables exist with respect to these incidents, the safety problem appears to involve two predominant failure modes.  The first failure mode involves pipe pullout from compression couplings.  Pipe pullout incidents resulted from different factors, such as cyclic fatigue caused by changing seasons, shifting soil, or improper installation.  The common factor shared by these pullout incidents, however, was that the compression fitting did not have adequate restraint to assure safety under service conditions.  The second failure mode involves leakage through the seal between the coupling and the pipe.  These types of failures generally occurred because the integrity of the seal degraded and allowed a leak path to develop.  Other contributing factors to incidents involving mechanical couplings have included leak surveys conducted in conditions where gas was prevented from properly migrating to the surface, and surveys performed with improperly calibrated or inappropriate equipment or conducted by insufficiently trained personnel. 

PHMSA also noted the efforts of several states to address mechanical coupling failures by performing studies and tests and implementing repair and replacement programs. 

PHMSA’s Advisory Bulletin

PHMSA’s Advisory Bulletin notes that identifying all failure-related criteria that pipeline operators should address is difficult, but advises gas distribution system operators using mechanical couplings to ensure compliance with Part 192 of the federal pipeline safety regulations by performing the following:

• Review procedures for using mechanical couplings, including coupling design and installation and ensure that they comply with manufacturer’s recommendations;
• Review leak survey procedures to ensure that leak surveys are conducted properly, taking into account other factors, such as weather conditions and calibration; and
• Review qualifications of personnel to ensure that they address leak surveys sufficiently.

PHMSA also advises operators of gas distribution pipelines using mechanical couplings to take the following measures to reduce the risk of mechanical coupling failures:

• Use Category 1 fittings only if mechanical couplings are used on pipe sizes ½ inch (Copper Tube Size) to 2 inch (Iron Pipe Size).  According to the American Society for Testing and Materials, 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.  To the extent that coupling issues arise on larger diameter pipe, PHMSA will revisit this issue. 
• Improve recordkeeping on specific existing couplings, including their type, installation, date, maintenance schedule, and any failures encountered to help identify a trend of problems that may occur on specific couplings or installation methods.
• Consider implementing a full replacement program if there are too many unknown factors 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 states or regions.

Implications

The measures identified in PHMSA’s Advisory Bulletin serve as a reminder to gas distribution operators of the importance of maintaining vigilance in ensuring the safety and effectiveness of mechanical couplings, not only on existing systems, but on new installations, particularly as the nation continues to increase its reliance on natural gas.  Undoubtedly, the importance of continued heightened awareness of safety issues will again be emphasized in PHMSA’s anticipated distribution integrity management regulations, expected to be issued this spring.  Finally, PHMSA’s recommendation that operators engage with regulators and other industry stakeholders reflects PHMSA’s “enterprise approach” of encouraging collaboration among government, industry and the public to identify trends, share information and best practices, and identify and craft solutions.