Stress-corrosion cracking (SCC) is a far more extensive problem on natural gas pipelines and hazardous liquid pipelines in Canada than in the United States, according to a draft version of a joint study released by the Office of Pipeline Safety (OPS) Friday.

The Interstate Natural Gas Association of America, which represents interstate gas pipelines, said SCC accounts for just 1.5% of the reportable incidents for pipelines in the U.S., while the National Energy Board reported that 15% to 20% of the failures in Canada were attributed to SCC, according to the nearly 200-page “Stress Corrosion Cracking Study.”

SCC forms on the exterior surface of underground pipelines as a group of hairline cracks. It often is the result of the interaction between pipeline stress, corrosion and certain environmental soil conditions.

Although the incident rate for SCC is “relatively small” in the U.S., it is a “widespread phenomenon,” said the report, which was coordinated with U.S. and Canadian regulators, major pipeline groups, pipeline companies and technical experts.

“SCC remains a significant issue largely because the industry’s understanding of this phenomenon is still evolving and practical methods of addressing SCC are not as mature as methods for addressing other failure causes.” While much remains to be learned about SCC, “an understanding is developing within the pipeline industry about how to effectively manage the SCC integrity threat,” it noted.

“There have been several recent occurrences of SCC failures in the United States, underlining the need for a coherent approach using the knowledge and tools currently available, as well as the need for further research,” the report noted.

The OPS, which is part of the Department of Transportation, has asked the public to comment on the draft report, setting a deadline of Nov. 21 for comments. Approximately one month after the public comment period, the OPS said it will issue a final report on SCC.

The entire report can be accessed on OPS’ website at

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