Hazards of Piping Dead Legs

The Pipeline Safety Trust has published a report to do with the recent gas pipeline explosion in Beaver County, Oklahoma. The failure occurred in a ‘dead leg’ pipe, which is defined as follows,

. . . a part of the pipeline that juts off the main pipeline, leads nowhere, and sees virtually no flow or movement but is still exposed to the product the pipeline transports. This dead leg pipe could have been an abandoned feeder pipe from an inactive production site.

The report goes describes why dead legs can be hazardous.

Because dead leg pipe can experience a near-complete lack of flow, the product, which in the case of the Phillips 66 pipeline is natural gas, can pool at the bottom of the “inactive” pipe allowing liquid to form and making the threat of internal corrosion severe.

“A prudent operator would either diligently monitor or remove dead leg pipes on their system and certainly would have isolated it from their active system,” Pipeline Safety Trust (PST) Executive Director Bill Caram said. “It is impossible to use smart pigs or other inline-inspection tools (ILI) to monitor dead legs for threats, making it harder to manage the integrity of the pipeline and contributing to their failure rate.

Although this report focuses on gas pipelines, dead legs are potentially hazardous in almost types of process and energy facility. Because there is no flow through them corrosive materials can build up. Then, if there is a leak, the contents of the entire pipeline system can flow out through that leak.

Hazards analysis teams should ensure that risks to do with dead legs are reviewed. If there is a possibility of corrosion the dead leg should be either removed or isolated with a blind flange.