PHMSA requires Hilcorp to replace its MGS fuel gas system pipeline A
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The federal Pipeline and Hazardous Materials Safety Administration is requiring Hilcorp to replace the fuel gas pipeline between the company’s Middle Ground Shoal A Platform and the MGS onshore facility.
A leak was reported in the fuel gas line April 1. (See story in April 11 issue of Petroleum News.)
PHMSA issued a corrective action order, CAO, on April 3, requiring reduced pressure in the fuel gas line, the Middle Ground Shoal A pipeline, completion of a temporary repair within 15 days and a shutdown of the line if that deadline could not be met.
On April 6 PHMSA amended that CAO, requiring Hilcorp to replace the line between Platform A and shore.
After the fuel gas leak was discovered April 1, Hilcorp initially reduced pressure in the fuel gas line, which carries transmission-quality natural gas, 98.67% methane.
It further reduced the pressure in compliance with the April 3 CAO.
On April 3 Hilcorp reported an abnormal operating condition - a pressure drop and increase in flow on the line. As a result, Hilcorp shut in the line. The company also reported that day that it was able to locate heaters which it could use to assist in freeze protection which had been provided by fuel gas from the MGS-A pipeline.
In response to the leak Hilcorp planned a multi-beam sonar survey and said it would attempt to get divers into the area when it was possible to do that safely.
The amended CAO specifies that the affected segment of the line, shut-in April 3, is to remain shut-in and may not be restarted until authorized by the PHMSA director under terms of the amended order.
Hilcorp then has 45 days to submit a replacement work plan and 365 days from the April 6 date of the order to complete the replacement.
Fifth leakPHMSA said this is the fifth leak on the MGS-A line since June 2014. Leaks previously occurred in June 2014 and August 2014, December 2016 through May 2017 and in 2019.
Most of the leaks “were determined to be caused by rock contacting the pipeline in areas where the pipeline was not continuously supported by the seabed,” PHMSA said; cause of the 2019 leak was “corrosion/weld discontinuity.”
Prior leaks were repaired with bolt-on split-sleeve clamps.
PHMSA said the 2014 leaks were 42 yards apart, the 2016-17 leak was some 2/3 mile from the previous two leaks and the current leak is in the general vicinity of the 2014 leaks.
A consent agreement following the 2016-17 leak required corrective measures, including integration of in-line inspection and sonar inspection results. That integration, PHMSA said, identified locations which required pipeline repairs or other mitigation measures. “Repairs and other mitigation actions included application of a pipeline clamp, coating repairs, and pipeline protection and stabilization,” the agency said.
PHMSA said state and federal agencies, including the Alaska Department of Environmental Conservation and the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service “have expressed concerns to PHMSA regarding damage to marine life in the Cook Inlet as a result of methane release into the water.”
Terms of amended CAOThe amended CAO requires that the MGS-A line remain shut-in and may not be operated until authorized by the PHMSA director.
Prior to restart, a restart plan must be approved, providing for adequate patrolling of the area during restart, which must occur in daylight. Pressure on the line may not exceed 65 psig until a higher operating pressure is approved by the director.
The restart plan must provide a repair plan.
The amended CAO says the affected segment of the line must be temporarily repaired by April 17 and permanently repaired by May 1, and Hilcorp must develop and implement a “Pipeline Leak Inspection and Repair Plan” for the MGS-A line.
Conditions are specified for removal of the pressure restriction.
Hilcorp is required to complete a root cause failure analysis and submit a final report to the director within 120 days. The analysis “must be supplemented or facilitated by an independent third-party and must document the decision-making process and all factors contributing to the failure.” Selection of an independent third party requires prior approval of the director.
A replacement work plan is required within 45 days and replacement must be completed within 365 days.
Line installed in 1965Hilcorp purchased Middle Ground Shoal Cook Inlet oil and gas facilities from XTO Energy in September 2015, a purchase which included the MGS-A pipeline.
The Middle Ground Shoal A pipeline is an 8-inch diameter line from the MGS onshore facility to A Platform, installed in 1965; the portion from the A Platform to C Platform was installed in 1967.
MGS Platform A was the earliest to be installed in Cook Inlet, in 1964, by Shell.
XTO, formerly Cross Timbers, purchased Shell’s Cook Inlet interests, including Platform A and Platform C, in 1998.
Both the MGS-A and MGS-B lines originally carried oil. MGS-A was converted to gas service in 2005. MGS-B no longer carries oil, but Hilcorp maintains a flow of water to that line and has told PHMSA that MGS-B could freeze in colder temperatures in a low-flow or no-flow condition, potentially causing a breach in that line.
Fuel gas provided by MGS-A is used to power boilers and the platform, providing freeze protection for MGS-B.
Hilcorp was ultimately able to mobilize heaters to the platform, allowing it to continue to flow water to MGS-B.
- KRISTEN NELSON