NEB unveils pipeline SCC study results

Canada's National Energy Board (NEB) has released a report and 27 recommendations by a panel on stress corrosion cracking (SCC) in pipelines. It rejected reduced pressures on lines as a solution to the problem. A three-member panel began a public inquiry in August 1995 after a series of pipeline ruptures in TransCanada PipeLines Ltd.'s gas pipeline system. The NEB report says SCC remains a serious concern for industry and regulators and contends the problem will worsen unless action is

Jan. 6, 1997

3 min read

A three-member panel began a public inquiry in August 1995 after a series of pipeline ruptures in TransCanada PipeLines Ltd.'s gas pipeline system.

The NEB report says SCC remains a serious concern for industry and regulators and contends the problem will worsen unless action is taken.

"Since SCC is a time-dependent process, without proper attention, it will worsen and be the cause of more pipeline failures," the report said.

The NEB panel recommends a comprehensive approach to the problem, including implementation by each pipeline company of an SCC management program, changes to the design of pipelines, continued research, establishment of an SCC database, improved emergency response practices, and information sharing.

The panel examined and rejected a reduction in pipeline pressures as a possible solution. The report says there is no clear evidence of a threshold level of pressure below which SCC will not begin and grow, so a pressure reduction will not prevent failures and will be very costly.

"We find that there are other measures that are more systematic, efficient, and effective in mitigating SCC and thereby promoting public safety," the report said.

The report adds that since decreasing pressure means a larger defect will be required before failure, pressure reduction should be considered as a temporary measure for sections of a pipeline system where there is a threat of imminent failure.

The NEB panel said SCC has caused 22 failures, including 12 ruptures on Canadian pipelines. Most of the SCC-related failures occurred since 1985 on pipelines coated with polyethylene tape and that were installed during 1968-73.

About 4% of Canadian pipelines in operation are in this category. Soil type, temperature, and stress on the line also are factors in causing SCC.

SCC has been recognized as the cause of pipeline failures in a number of countries, including the U.S., Australia, Iran, Iraq, Italy, Pakistan, Saudi Arabia, and those of the former Soviet Union.

The report said SCC affects both oil and gas pipelines across Canada and is more widespread than previously believed.

The NEB has accepted the panel's conclusions and soon will disclose steps to implement them.

The Canadian Energy Pipeline Association said it is pleased with the recommendations and has already established a database to track SCC incidents.

Preliminary investigation into a gas pipeline explosion at Vermilion Bay, Ont., earlier this month indicate SCC was not a factor. The line showed signs of general corrosion. TransCanada PipeLines is replacing 157 ft of pipe.