At around 3:00 p.m., an operator noticed a leak coming from a 40,000 m³ diesel tank at a port oil terminal. The fuel flowed out of the bottom of the tank at a rate of 2 m³/h and into its bund. The fuel was transferred to another tank. A trench to collect the fuel was excavated and covered with a liner. A pump was set up to recover the liquid. The firefighters arrived at the terminal. It took two days to pump out and drain the tank. Emergency services recovered 22 m³ of diesel and collected 26 tonnes of contaminated soil and 6 tonnes of liquid waste that were disposed of at a special waste incineration plant.

Cracked weld at the bottom of the tank

A 2.5-m-long crack was found in the weld joining the tank’s shell to its bottom. The bottom is surrounded by an annular edge (or annular plate) that supports the tank’s shell and to which the tank’s bottom plates are also welded. An assessment of the tank’s bottom revealed multiple defects:

• the annular plate’s remaining thickness was 50% less than the original thickness in places;
• significant thickness losses on the bottom plates;
• localised settling of the tank.

Failure to take corrosion defects sufficiently into account

The last ten-year inspection of the tank took place in 2009. At that time, it was found that the tank had sunk by 280 mm. To prevent any further sinking, the operator poured a concrete collar around the tank. In addition, external corrosion had been discovered, and had resulted in a significant reduction in the thickness of the bottom plates. The section of the annular plate near the crack has not been inspected due to a lack of equipment suited to its geometry.

Since the event, the operator has promised to;

• completely replace the annular plate before putting the tank back into service;
• patch repair the bottom plates where thickness losses exceed 40%;
• check the thickness of the weld between the shell and annular plate at each ten-year inspection.