Safety Bulletin 2003-01

Spring 2003

EMERGENCY SHUTDOWN VALVE RISERS ON PIPELINES

A recent sour gas pipeline failure highlighted the need for pipeline companies and pipeline contractors to observe all regulations and requirements when constructing and operating pipelines.

The sour gas pipeline failed at an emergency shutdown (ESD) valve riser. The failure resulted in a release of sour natural gas and small quantities of associated liquids. The line was shut in and remained so until the EUB conducted an extensive investigation of the incident and was satisfied that all safety, construction, and operational concerns were completely addressed.

The following factors were found to have contributed to the incident

• The direct cause of the failure was an improper weld on the pipeline at the ESD valve riser.
• An indirect cause was improper backfilling, which caused high stress at the weld.
• A second indirect cause was inadequate supervision or inspection of the welding and installation, which failed to prevent, or detect, the weld defect at the riser and identify the inadequate backfilling and compaction procedures.
• A related factor that contributed to the volume of the release was that the ESD valves did not close immediately after the failure. They were closed manually prior to the automatic set point being activated. This was due to the low-pressure trip set point of the valves being set considerably lower than the pipeline’s normal operating pressure. As a result, the gas leak continued for a longer period of time.

Recommendations

Pipeline owners and engineers should ensure that for any pipeline construction project, a complete and thorough quality assurance protocol be implemented in order to ensure that:

• The contractors understand the design features specified, so that construction is properly executed in accordance with the design.
• Specific procedures are developed for critical functions, such as materials specification, welding or backfilling, and are followed as specified.
• Critical procedures inspection criteria are developed and inspectors use those criteria.
• Any deviations from the original design are reported and approved by the project engineer, or alternatively, are corrected to the design specifications.
• ESD valve setpoints are appropriate for the expected service.

Contact

For more information about pipelines in Alberta, contact the Alberta Energy and Utilities Board Pipeline Section at (403) 297-8432, (403) 297-8967, or (403) 297-8148.
For more information about on-site inspections of energy facilities, communicating with residents and landowners, and oil and gas incidents and emergencies, contact the Alberta Energy and Utilities Board Field Centre near you:

To call toll-free, dial 310-0000
Bonnyville (780) 826-5352
Drayton Valley (780) 542-5182
Grande Prairie (780) 538-5138
Medicine Hat (403) 527-3385
Midnapore (403) 297-8303
Red Deer (403) 340-5454
St. Albert (780) 460-3800
Wainwright (780) 842-7570