Weight on Keystone pipeline led to coating failure and oil spill
Materials Performance has released an article by Ben DuBose referencing the Pipeline and Hazardous Materials Safety Administration, PHSMA, which describes the root cause of a recent rupture in a segment near Amherst, South Dakota, USA.
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.
This pipeline has been a target of protest and construction was halted by the Obama administration, only to be given the green light by incoming President Donald Trump.
The 30" (762 mm) diameter pipe was constructed of API 5L X70 line pipe, with a double-submerged arc welded seam and coated with a fusion-bonded epoxy coating. The protective coating was part of the corrosion protection solution originally installed by pipeline operator TransCanada.
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 5000 bbl (794,937 ℓ) of oil leaked from the crude oil transmission pipeline near Amherst, South Dakota, USA. This pipeline segment, known as the ‘Phase 1 Line’, is part of Keystone’s massive 1082 mile (1741 km) liquid pipeline system that runs from Hardisty, Alberta, Canada, to Patoka, Illinois, USA. The release occurred in a rural agricultural area.
The pipeline operator detected a pipeline pressure drop and an increase in flow rate on the line and shut down the line within minutes and issued a corrective action order (CAO) to the operator requiring additional tests to identify and address any threats to the integrity of the system.
The company excavated the failed section of the pipe and shipped it to the US National Transportation Safety Board (NTSB)’s (Washington DC, USA) metallurgical lab in Ashburn, Virginia, USA, for further evaluation. 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 1046 psig (7.21 MPa). This was done to ensure a safe and gradual increase in the volume of oil moving through the system.
“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. He suggests that weights were placed on the pipeline in areas where water could potentially result in buoyancy concerns.
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.
A remedial work plan (RWP) calls for additional information from the operator, including a proposal to analyse 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, in-line inspection reports and all other data pertinent to the analysis of the failed pipe.
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 that it plans to comply with any future PHMSA orders and requirements as a result of the incident to ensure the pipeline’s integrity.
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