By AUSTIN LOVE
Council Project Manager
In 2012, Alyeska identified a 6 inch wide area of external corrosion on crude oil piping near the end of one of their oil-loading berths, known as Berth 5, at the Valdez Marine Terminal. Corrosion in the 48 inch diameter pipe is of particular concern, as it is located over water.
This corrosion was caused because this section of pipe was not covered with an anti-corrosion coating during construction of the terminal. When the area of corrosion was originally discovered, it was not deemed substantial enough for significant repair and was covered with an anti-corrosion coating to prevent further deterioration. However, re-analysis in October found that the corrosion was more severe than initially determined. At one approximately 1.5 inch diameter spot, Alyeska concluded that about 80 percent of the metal had been lost due to corrosion. Wall loss of 80 percent is a typical threshold, used by regulators and industry, at which mandatory repair is needed even if engineering analysis deems conditions to be safe for operations to continue. Upon this discovery of significant corrosion Alyeska alerted the council and regulators.
This segment of piping routinely has 100,000 barrels of crude oil flowing through it per hour when tanker ships are being loaded at the Valdez Marine Terminal. If a leak developed at this location, it is estimated that about 6,000 barrels (252,000 gallons) of oil would spill into Port Valdez before an upstream valve could stop the flow of oil.
At that time, Berth 5 was the only operating berth at the terminal while Berth 4 was down for maintenance. To mitigate the increased potential for an oil spill from this corroded piping section, Alyeska initiated a number of temporary measures. They immediately reduced the maximum loading rate from 100,000 barrels per hour to 75,000 barrels per hour. Precautionary booming and oil containment structures were setup to mitigate the possibility of leaks from the weakened piping sections. Within a few days of notifying regulators and the council, Alyeska fabricated and installed a carbon steel piping clamp that was bolted around this area of corrosion. The clamp does not provide any structural support for this piping segment, rather it was installed as extra precaution to prevent a crude leak from the weakened pipe section. This pipe clamp is not intended to be a permanent fix although it can remain in place for an indeterminate amount of time until a permanent solution is found. In December 2014 a brace was installed just downstream of the corroded area to reduce the forces and stress associated with tanker loading on the corroded segment.
Alyeska hired a pipeline engineering firm to evaluate the operational limitations associated with this corroded piping. The firm’s analysis, completed in December 2014, led to the conclusion that the pipe can be safely operated at a maximum pressure of 400 pounds per square inch (psi) and sustain momentary pressure spikes of 440 psi. Normal operating pressures of this piping are below 200 psi and the largest recorded pressure spike since 2001 was 313 psi. The firm’s investigation determined that an immediate permanent repair was not warranted but that one should be completed soon.
Alyeska hired another engineering firm to comprehensively evaluate the structural integrity of the crude oil piping and provide design recommendations for permanent repair. Possible permanent repairs include a welded on metal sleeve, a specialized composite pipe wrap, or replacing the section with new pipe, which is considered by Alyeska as the last option. The second analysis with repair recommendations should be completed by February.
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