Learning the lessons from the spill
Alyeska tightens loading arm test procedures and revisits valve design in wake of Berth 5 incident at Valdez Marine Terminal
Alyeska Pipeline Service Co. has tightened its procedure for testing loading arms at the Valdez Marine Terminal in the wake of the September oil spill incident at the terminalís berth 5, Scott Hicks, the terminal manager, told the Prince William Sound Citizensí Advisory Council board on Jan. 18. The company is also planning a project to replace valves in the loading arms using an improved valve design - leakage around a valve was a root cause of the oil spill incident, Hicks said. However, Alyeska has largely attributed the incident to human error. A work crew testing the berth 5 loading arm had inadvertently left the arm in an unsafe condition during a pause in a loading arm test.
Routine valve testHicks explained that the incident occurred during routine testing of a ball valve designed to prevent fluids spilling from the loading arm when the loading arm is not in use. The fluids are subject to hydrostatic pressure as a result of the loading berth being at a lower elevation than the valve system used to control the flow of oil to the tanker loading berth. The ball valves do tend to leak slightly, with the rate of leakage increasing over time as a result of wear on the ball seatings, Hicks explained. But the facility is designed so that fluids leaking through the valve remain within the terminalís oil containment system, thus preventing any leakage of oil to the surrounding environment. Under an agreement with the U.S. Coast Guard, Alyeska tests the valves annually, to ensure that the leakage rates do not exceed specified limits. Every few years valves have to be replaced, when leakage rates become too high. The testing involves draining as much oil as possible from a loading arm, pumping seawater into the arm, and then raising the fluid pressure to about 190 pounds per square inch. The procedure works best at high tide, Hicks said.
Started at low tideOn the fateful day of the berth 5 incident, a work crew started to conduct the test at low tide but was unable to raise the fluid pressure quite high enough. The crew decided to defer the test to high tide, later in the afternoon, and meanwhile left the seawater pump in place while conducting other tasks. Unfortunately, however, there were a couple of valves in the system that the crew did not think to close. With relatively high-pressure seawater in the arm and a somewhat leaky ball valve, seawater flowed back out through the seawater pump and into the water of Port Valdez. The arm held some residual crude oil, about half of which escaped into the port along with the released seawater. In all, about 70 gallons of oil escaped, Hicks said. A rapid spill response ensued, using boom to contain the spilled oil around the berth area. Protection was also put in place for the Valdez Duck flats and the Solomon Gulch salmon hatchery. Fishing vessels under contract to Alyeska for spill response services mopped up the spilled oil using oil skimmers. It took about four days to complete the cleanup, Hicks said.
Lessons learnedBased on lessons learned from the incident, Alyeska has tightened up its loading arm testing procedure, to prevent a repeat of a similar error. The company has also tested all of the loading arms at the terminal, to ensure that there is no external leakage of fluids. However, given that the leakage of the ball valve in the berth 5 arm underlay the spill, the company has found a superior valve design and has initiated a project to replace the existing valves. The valves are large and have to be manufactured - Alyeska anticipates replacing the valves in 2019 and 2020, Hicks said.