On November 12, 2008, a tank managed by Allied Terminals, Inc. in Chesapeake, Virginia, failed and imploded. Around 2.1 million gallons of liquid fertilizer flooded the surrounding areas, with residents forced to evacuate the area for cleanup. The spill also reached the Elizabeth River, which was 1,000 feet from the tank, named as Tank 201. Around 200,000 gallons of liquid fertilizer remained unaccounted for after cleanup operations.
Two workers – a welder and his helper, both from contractor G&T Fabricators, Inc. – were seriously injured in the tank collapse. The two had been working on the tank when it collapsed. At the time of the incident, the tank was being filled with the fertilizer to enable the welder to spot and repair leaking rivets. Unfortunately, as an investigation by the US Chemical Safety Board (CSB) uncovered, a vertical weld seam in the tank failed before the liquid fertilizer even managed to reach the safe fill height. This caused the tank to implode and the liquid fertilizer to flood the area.
So why did the tank fail?
In general, Allied Terminals failed to meet API 653, which is the industry standard for inspection, repair, alteration and reconstruction of vertical, cylindrical, aboveground steel storage tanks. This has been developed by the American Petroleum Institute, and has been incorporated by reference into some states’ storage tank regulations.
Among the specific guidelines that Allied Terminals neglected were the following:
- Modifications not approved by qualified professional; welds and welders did not meet industry standards. The tank was constructed back in 1929, and was originally used to store petroleum products. These petroleum products were “lighter” and less dense compared to the liquid fertilizer. This required Allied Terminals to propose tank modifications for it to be able to store more liquid fertilizer; the modifications included the replacement of the original vertical riveted joints with butt-welded plates. While these modifications were in line with API 653, Allied Terminals did not have an independent inspector - or engineer specializing in storage tank design – check and approve the modifications.
The welds used by welders from G&T Fabricators were not up to par with industry standards. According to the CSB’s final report on the incident, the welders themselves were not qualified to perform the modifications. Allied Terminals did not even have these very modifications approved by
- The safe fill level was not computed properly. Allied Terminals signed up HMT Inspection, Inc. to determine the safe fill levels for their tanks. Instead of using the minimum measured shell/plate thickness, HMT used the average of 10 plates’ thickness measurements. Using the minimum measured thickness, the safe level would have been 1.5 inches less than the level at which the tank failed.
- Allied Terminals did not have post-welding inspection procedures, such as spot radiography, performed on the newly-modified tank. This could have ensured that the tank is structurally sound before trying to fill it. Spot radiography is also needed to calculate the tank’s maximum liquid levels.
- Allied Terminals did not have specific safety guidelines for work on or around tanks that are filled for the first time following major modifications.