Oil spill during transfer operation, July 17, 2010, Speyer, Germany

At around 3 a.m., a leak occurred following a pipe compensator failure during the transfer of a hydrocarbon mixture from a river barge to a refinery tank farm. The previous day, measures were taken to prepare for the transfer of 500 t of C5-C6 n-alkanes (a highly flammable liquid, highly toxic to aquatic organisms) from a barge to a 1,000 m³ fixed-roof tank. A flexible hose (DN 80) is installed on a branch of the pipe rack (DN 150) for connection to the tank. A checklist describing all the manual steps is used, and 2 checks of the connections and piping are carried out by the operations manager at the end of the preparatory work and at 0:00 by a night shift operator. At 0:30 am, the barge is moored to the wharf and a sample is taken for analysis by the laboratory. At 1:30 a.m., after receiving the analysis results, the 50 m³/h pump was started up and an operator observed the flow in the tank (acoustic check, flow noises). At around 1.45-2 a.m., the pump broke down twice for undetermined reasons. The installations (piping, valves, measuring, control and regulation equipment) are checked; no faults are found. At 2:30 a.m., an inspection is carried out on the piping between the tank and the port, and no leaks are found. At 2.45-3 a.m., the boat's pump was restarted with a flow rate of 100 m³/h. At 3:10 a.m., an operator in the control room noticed discrepancies between the pump's speed and the state of the tank's filling, and carried out a new inspection of the pipes, which revealed a pool of hydrocarbons. The transfer was immediately stopped, and the site and local fire departments were alerted. Repeated stoppages and restarting of the pump at 100 m³/h instead of 50 m³/h caused a pipe expansion compensator to burst. Investigations revealed a water hammer phenomenon caused by: the 450 m long pipe which cannot be positioned at a constant incline due to geographical constraints and site configuration; the pump's repeated failure, leading to cavitation and the formation of cavitation bubbles; the pump operation at high speed, leading to overpressure in excess of piping design pressure (16 bar); the decreasing cross-section (DN 150 / DN 80), unfavorably placed support devices and the design of the expansion compensator favoring the breaking point. The soiled surface area is estimated at 320 m². The puddle was covered with foam to prevent evaporation, then pumped out the following day by a specialist contractor. Gas measurements taken outside the site showed that the Lower explosion limit (LEL) was not exceeded. The quantity spilled is estimated at 80 t of product; 20 to 30 t were recovered during emergency measures, but 50 to 60 t penetrated the unsealed soil (sandy ground). A long-term procedure for decontaminating the soil, drilling wells and pumping hydrocarbons into the water table was put in place, at an estimated cost of 480 kEuros. A system with a vacuum-breaking function has been installed to limit the risk of water hammer resulting from failure to control the technical characteristics of the installations: flow-measuring equipment at the wharf detects drops in outlet flow and activates an injection of compressible gas (nitrogen) so that masses of fluid in motion do not collide with static masses of fluid, causing pressure peaks for which the piping is not designed. In addition, the number of tapered sections and expansion joints is reduced to the strict minimum. Following rehabilitation of the plant, there is now only one product transport line between the port and the tanks. The operator is repairing the compensator at a cost of 10 kEuros, plans to increase the number of surveillance rounds and the loading/unloading instructions for site personnel and crews are being checked and updated