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A May 1 gas line repair deadline
The Pipeline and Hazardous Materials Safety Administration has sent a letter to Hilcorp Alaska proposing an order to set a deadline of May 1 for repairing a leaking subsea gas pipeline in the Cook Inlet. PHMSA, an agency within the Department of Transportation, regulates pipeline safety for the federal government.
If the pipeline is not repaired by May 1, Hilcorp must shut the line down until a restart is authorized, PHMSA proposes. Meanwhile Hilcorp must maintain the gas pressure in the line at as low a level as possible. And, within two weeks, the company must file a pipeline leak inspection and repair plan.
The leak was discovered on Feb. 7 by a Hilcorp helicopter at a location between Nikiski on the Kenai Peninsula and the offshore Middle Ground Shoal field’s Platform A. The pipeline, which lies in a water depth of 80 feet, supplies dry processed fuel gas to the A, C, Dillon and Baker platforms. According to the PHMSA letter, Hilcorp conducted the helicopter surveillance flight in response to observed anomalies in pipeline flow data.
Diving hazards Recognizing the very high danger associated with diving operations in the neighborhood of the leak in current sea ice conditions, especially given the extreme tides in the inlet, PHMSA is giving Hilcorp until May to effect a repair. Hilcorp has estimated that it will not be possible to conduct safe diving operations until at least late March, and possibly the end of April. The company has assessed that the use of divers is the best approach to safely fixing the pipeline breach.
The PHMSA deadline also recognizes the environmental risks associated with shutting down the pipeline until the repair is completed. A shutdown of the pipeline could result in the leakage of some residual crude oil in the line - the line had previously been used to carry oil. Moreover, the cessation of the fuel gas supply would require a shutdown of the transportation of produced crude oil from an offshore platform through another undersea line. And, given the subsequent possibility of that line freezing in current cold conditions, a breach in the oil line and a subsequent oil spill could result, the PHMSA letter says.
Hilcorp has, however, minimized gas flow through the line by shutting down non-essential operations on the offshore platforms that the line supports.
Installed in 1965 The PHMSA letter says that the broken gas line is eight inches in diameter and is encased in concrete. It was installed in 1965.
The pipeline has suffered leaks twice in the past: in June and August 2014, the letter says. These leaks, which occurred in ice-free conditions, were determined to have been caused by abrasion from rocks contacting the pipeline at locations where the seabed did not support the line, the letter said. Conducting repairs involved installing bolt-on, split-sleeve clamps. The leaks were 42 yards apart and about two-thirds of a mile from the current leak.
The abrasion is thought to be caused in part from the relative movement of the pipeline and rocks under the effect of vortex-induced vibrations of the pipeline. And, with these vortex-induced vibrations have been a known threat for years, Cook Inlet pipeline operators typically monitor subsea pipelines annually, to identify sections of lines unsupported by the seabed. If necessary, additional support may be added to these sections, the letter says.
The design of the damaged gas line does not allow the use of in-line inspection tools. Pressure testing was conducted on the line in 2005. And, although Hilcorp conducts annual side-scan sonar or multi-beam echo-sounder surveys, these surveys do not provide enough information to be able to determine whether there are problems such as eroded pipe, rock impingements, dents, gouges or missing concrete coating, the letter says.
The U.S. Coast Guard has been notifying mariners of the leak but has not at this point implemented a safety zone around the leak location. Currently the agency sees the risk to life and property to be low, although the risk could increase when the sea ice dissipates. The Federal Aviation Administration has enforced restricted airspace one nautical mile around the leak, to an altitude of 1,500 feet, the PHMSA letter says.
In a March 8 press release, Hilcorp said that to date no significant impacts to wildlife or the environment have been observed and that the gas release does not pose a threat to the general public. The company said it is maintaining a lower pressure in the pipeline and that the escape rate of gas is about 229,000 cubic feet per day. A response team is ready, with equipment staged, to commence repairs as soon as it is safe to do so, the company said. Hilcorp also said that it has been conducting air and water sampling and is working with the Alaska Department of Environmental Conservation on a more comprehensive plan for the monitoring of fish and wildlife; air and water quality; sound; and ice conditions.
- ALAN BAILEY
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