In the aftermath of the collapse of a 2-million-gallon liquid fertilizer storage tank at its Chesapeake, Va., facility (GM Dec. 1, p. 10, Nov. 24, p. 13, Nov. 17, p. 12), Allied Terminals now faces the task of having to drain and inspect, both internally and externally, three similar tanks for the same faulty welds found by federal investigators to be the cause of the Nov. 12 catastrophic incident.
The U.S. Chemical Safety Board (CSB) issued the “urgent recommendation” for Allied to take immediate action after concluding that the failure of Tank 201, which contained an aqueous solution of urea and ammonium nitrate fertilizer, likely resulted from defective welds on the tank wall performed in 2006 to strengthen four fertilizer tanks constructed around 1929 by replacing vertical riveted seams. “This action is designed to protect the safety of workers, the public and the environment,” said CSB Chairman John Bresland. He also disclosed that CSB is advising Allied to reduce the hazard from the remaining tanks immediately by lowering the maximum safe fill height, and to retain a qualified tank engineering firm to assess the tanks’ safety. He indicated the CSB request is in response to concerns of nervous residents and local officials, and that the immediate analysis should be completed within 30 days, with the results provided promptly to the city.
Allied is also being requested to develop and implement a corrective action plan for any identified deficiencies in the tanks. The tank collapse seriously injured two contract workers, who were hospitalized. Two members of the public who tried to aid the injured men required treatment likely related to exposure to ammonia vapor from the released fertilizer. The fertilizer overtopped a containment dike and flooded sections of a nearby residential neighborhood, requiring ongoing remediation of the soil. At least 200,000 gallons of spilled fertilizer could not be accounted for, and some reached the nearby Elizabeth River, which flows into the Chesapeake Bay.
“We found a number of welding defects where the modifications were made, including incomplete penetration of the welding metal into the joints,” said CSB Lead Investigator Robert Hall, P.E. “These welding defects likely weakened Tank 201 and led to its failure when the liquid was raised to a level slightly below the tank’s recommended safe fill height.” In the course of investigating the collapse of Tank 201, CSB investigators determined that three other large fertilizer tanks that were welded during the same time period likely have welding defects similar to Tank 201, including insufficient reinforcement, porosity, and weld undercut, which could cause the tanks to fail. The closest of the three large tanks is located 250 feet from homes.
Investigators said that the level of risk could not be quantified based on their external visual examination of the welds, and that a thorough, independent engineering analysis should be conducted, including testing to check for the internal defects in the welds.
According to a tank inspection authority whose business is located in Norfolk only 15 minutes away, Allied faces a tricky job shifting product from tank to tank so that a thorough inspection and verification of the panel welds to be completed. Gary Boley, who founded, owns, and operates InterSpec LLC, said the tasks will have to be done tank-by-tank so that product can be safely and efficiently transferred. Boley, who has not been on the Allied scene and has not been invited, said he suspected faulty welds even before CSB made its evaluation. “The welds will have to be inspected inside and out,” Boley told Green Markets. “The only way an X-ray can do a thorough job is from the inside.” He said he would be surprised if the other tanks didn’t show the same problems as the one that collapsed.
According to information provided by CSB, after the welding of the four fertilizer tanks and before the collapse of Tank 201, Allied Terminals hired HMT Inspection, a Texas-based tank engineering firm with offices worldwide, to examine each tank in accordance with existing industry safety guidelines for petroleum tanks. While HMT’s report did not identify the welding defects that led to this failure, it did recommend a “safe fill height” for each tank. However, the Nov. 12 collapse of Tank 201 occurred while the tank was being filled to a level about three inches below the 27-foot safe fill height recommended by HMT.
Bresland said the remainder of the investigation would focus on understanding why the welding defects occurred, why the tank deficiencies were not detected and corrected, and whether improvements are needed in the oversight of above-ground storage tank safety. “At this stage in the investigation, it appears that no federal, state, or local agency has clear regulatory and enforcement responsibility for the safety of non-petroleum aboveground storage tanks,” he said. “Because of the hazard such tanks can pose, the CSB will examine whether additional safeguards are necessary at the national and state levels.”