The installation of a weight on the Keystone oil pipeline in South Dakota upon its construction in 2008 appears to have caused mechanical damage to the coating, leading to a recent rupture and oil spill, according to a preliminary investigative report1 issued by the U.S. Pipeline and Hazardous Materials Safety Administration (PHMSA) (Washington, DC, USA).
The 30-in (762-mm) diameter pipe was constructed of API 5L X70 line pipe manufactured by Berg Steel Pipe Corp. (Houston, Texas, USA), with a double-submerged arc welded seam and coated with a fusion-bonded epoxy coating, according to the report. The protective coating was part of the corrosion protection solution originally installed by pipeline operator TransCanada (Calgary, Alberta, Canada) on the Keystone system.2
Weights are used to keep pipelines in place and reduce the risk of damage to the line if water levels rise. In this case, however, initial findings show the weight caused damage to the company’s corrosion-resistant coating.
On the day of the incident, an initial estimate of 5,000 bbl (794,937 L) of oil leaked from the crude oil transmission pipeline near Amherst, South Dakota, USA. The failure occurred on November 16, 2017, on the ~47-mi (75-km) pipeline segment known as the “Phase 1 Line,” which is part of Keystone’s massive 1,082-mi (1,741-km) liquid pipeline system that runs from Hardisty, Alberta, Canada to Patoka, Illinois, USA. The release occurred in a rural agricultural area.
Upon detecting a pipeline pressure drop and an increase in flow rate on the line, the pipeline operator shut down the line within minutes. PHMSA sent four technical experts to the spill site the next day. On November 28, PHMSA issued a Corrective Action Order (CAO) to the operator requiring additional tests to identify and address any threats to the integrity of the system.
As part of that request, the company excavated the failed section of the pipe and shipped it to the U.S. National Transportation Safety Board’s (NTSB) (Washington, DC, USA) metallurgical lab in Ashburn, Virginia, USA for further evaluation. That evaluation, which remains ongoing, could determine whether the line suffered any damage from corrosion, which may have resulted from coating failure.
Though TransCanada replaced the damaged section of the pipeline within two weeks of the leak to enable its restart, the CAO also mandated the line be operated at 20% lower pressure than normal, including a maximum discharge pressure at the nearest pump station of 1,046 psig (7.21 MPa). This was done to ensure a safe and gradual increase in the volume of oil moving through the system.
“We are following a strict startup protocol that includes visual checks from the land of valve sites and pump stations as well as aerial inspections along the pipeline right-of-way,” TransCanada says in a statement.
The investigation is ongoing, but PHMSA says its preliminary information shows the rupture to have characteristics of mechanical damage from original construction. “Preliminary information indicates the failure may have been caused by mechanical damage to the pipeline and coating associated with a weight installed on the pipeline in 2008,” Alan K. Mayberry, PHMSA associate administrator for pipeline safety, writes in the CAO.
Weights were placed on the pipeline in areas where water could potentially result in buoyancy concerns, Mayberry explains.
According to the CAO, TransCanada was operating pigging equipment including a cleaning tool and a SmartBall† leak detection tool near the rupture before the leak. “Both tools passed the site prior to the rupture without identifying any oil leakage from the pipeline at this location,” Mayberry writes, adding that there is no indication that the tools contributed to the release.
As part of the order, PHMSA also mandated the submittal of a remedial work plan (RWP) to the agency’s director within 120 days of the order’s receipt. That plan calls for additional information from the operator, including a proposal to analyze available data on other weight locations throughout the Keystone pipeline to see if there are similar characteristics to the site of the coating failure near Amherst.
The RWP also specifies that the operator must perform internal inspections with technologies appropriate to identify mechanical damage and/or indications of cracks with similar characteristics to that of the failure site. The plan must include a review of original construction records, inline inspection reports, and all other data pertinent to the analysis of the failed pipe. Through utilizing that information, integrating all available data, and performing root cause analysis, the RWP should be designed to prevent reoccurrence, Mayberry says.
In addition, within 90 days of receiving the NTSB’s metallurgical analysis, the CAO calls on the operator to complete a root cause failure analysis (RCFA) and submit a final report to PHMSA. The RCFA must be supplemented or facilitated by an independent third party, and its purpose is to document the decision-making process used in the analysis and all factors contributing to the failure.
“The final report must include findings and any lessons learned and whether [they] are applicable to other locations on the Keystone pipeline,” Mayberry writes.
To ultimately return the pipeline to its pre-failure operating rate, the company must submit a written request to the agency demonstrating that full restoration to its pre-failure pressure is justified “based on a reliable engineering analysis showing that the pressure increase is safe and considering all known defects, anomalies, and operating parameters.”
PHMSA says its failure probe is ongoing, adding that the CAO could be amended based on further findings during the investigation. In a separate statement, TransCanada says it plans to comply with any future PHMSA orders and requirements as a result of the incident to ensure the pipeline’s integrity.
† Trade name.
Source: PHMSA, www.phmsa.dot.gov.
1 “Keystone Pipeline Release—Britton, S.D.,” PHMSA News, Nov. 28, 2017, https://www.phmsa.dot.gov/news/keystone-pipeline-release-britton-sd (Dec. 20, 2017).
2 “Ten Keystone XL Safety Features You Might Not Know,” TransCanada Stories, Oct. 23, 2013, http://blog.transcanada.com/ten-safety-features-of-keystone-xl-you-might-not-know/ (Jan. 8, 2018).