In an oil refinery, a leak was detected on crude oil tank A607 with a nominal capacity of 60,000 m³ and filled at over 50%. Ground pollution covered several square metres from the extreme western edge of the tank until reaching the sump located a few metres from the tank shell. According to the operator, who was unable to visually observe any external corrosion either on the shell or on the visible section of the tank bottom and who relied on general renovation works conducted in 2000, with complete replacement of the tank bottom and foundation reconstruction and with feedback provided by other leaks (which had evolved slowly in a controlled manner), the tank’s structural integrity was not considered suspect. The tank was kept operating under daily monitoring that took the form of rounds with: introduction of sand dams in the retention basin, regular pumping of spilled hydrocarbons, creation of a gutter to channel flow towards the sump, and replacement of the surface layer containing polluted gravel.

Six successive filling operations were conducted through Sept. 6th, when during the evening a sudden increase in the leak flow rate (20 m3/hr) was noticed at several points. On Sept. 7th, it was decided to drain the tank, and the crude oil was routed to the site’s distillation units. The Classified Facilities inspectorate was informed of the event in the afternoon of the next day. In addition to verifying the tank’s complete drainage, a technical inspection on Sept. 13th confirmed the presence of a few areas of seepage around the edge of the tank base, along with pollution over the entire retention basin surface area (and puddles of oil several centimetres thick in some areas). The inspectors also identified contamination in retention tanks A209 and 201, which were independent of tank A607.

A decree ordered the issuance of incident reports on all 3 of these tanks as well as cleanup of the corresponding retention basins.

The expert appraisal of tank A607 revealed many internal corrosion pits on the tank bottom metal sheets and along welds with a leaky zone, plus the absence of a lining to protect against internal corrosion when replacing the bottom in 2000; two additional cases of leaks on this site’s crude oil tanks would be identified in 2007 and 2009 (ARIA 33077 and 36502).

The operator installed an epoxy lining on the tank bottom prior to resuming operations and decided to extend this measure to all other onsite crude oil tanks.

A penal court fined the operator €800 for failing to file the incident with the Classified Facilities Inspectorate.