Cold weather-related incidents have occurred in gas distribution systems, gas transmission systems, and hazardous liquid transmission systems. By far the most common cause of such incidents is frost heave, acting on buried pipe. However, a large number of less-frequent incident scenarios related to cold weather have been described in PHMSA’s reportable incident database, affecting both buried and above-ground installations. All types of pipe materials found in distribution service have been affected, however piping with certain attributes appear to have higher-than-average susceptibility. These are: cast iron pipe, pipe of unknown material type, steel pipe installed prior to 1950.
IM principles require that the operator consider integrity threat interaction. Frost heave or snow load might be readily tolerated by some materials or a piping system in sound condition, while low-ductility materials or pipe joints made by vintage techniques may remain reliable absent certain outside forces, however, when these circumstances exist simultaneously the likelihood of a failure is significantly greater. Systems of the type listed above in locations susceptible to frost heave therefore represent potential interacting-threat situations.
Piping systems having the attributes listed above and located in areas known or suspected to be susceptible to frost heave or thaw settlement should be identified and considered for condition monitoring or mitigation activities. While frost heave was responsible for the largest number of incidents, other causes have also been identified, including snow and ice falls from rooftops, confined freezing of water trapped in components, or build-up of ice where standing water accumulates around risers or under low-mounted above-ground components.
Condition monitoring could involve a range of activities, including but not limited to:
- Periodic visual site inspection during cold weather months by someone qualified to recognize evidence of frost heave or thaw settlement;
- Examination of piping buried above the frost line for evidence of deflection at joints during routine excavations;
- Visual inspection of sites for frozen standing water around risers or under equipment mounted low to the ground.
Mitigations could include but are not limited to:
- Replace iron pipe, unknown-material pipe, and threaded steel pipe with plastic or welded steel pipe in locations known or suspected to be susceptible to frost heave;
- Remediate drainage or soil conditions that promote frost heave at susceptible sites;
- Correct drainage conditions that promote accumulation of standing water around risers or under low-mounted equipment;
- Drain trapped moisture from equipment during routine maintenance or inspections.