At around 2:35 p.m., a hydrocarbon leak was suspected on a transport pipeline during a fuel transfer operation between the port of Le Palais and the tanks located in the Belle-île oil depot. The leak was confirmed using a material balance method and the performance of water tests. The operator estimated that the leak involved 2,700 litres of hydrocarbons (gasoline, diesel fuel and domestic heating oil). No trace of pollution was visible on the surface of the piping. Tests were conducted to precisely locate the leak. During these tests, a perforation was discovered on the lower generatrix of the pipeline.

Numerous operations were undertaken to seal the pipeline

Two weeks later, the Prefect of Morbihan issued an emergency order to supervise the repair work and to suspend all hydrocarbon transfer operations until the entire pipeline had undergone leak testing. In the month following the suspected leak, two successive operations were performed to replace the pipes, but the leak tests had proved unsatisfactory. The operator concluded that other leaks were present and decided to replace piping over a longer stretch of the line.

Causes of the damage

An analysis of the damaged piping highlighted small areas of “pitting” type perforation caused by an internal corrosion mechanism. In February of the year preceding the leak, an intelligent pig used to inspect the line had not detected these areas. Its detection accuracy was insufficient in relation to the small size of the defects (less than 5 mm).

Generally speaking, the piping’s internal wall showed signs of widespread wet corrosion associated with the system’s operating method, which consisted of filling it with seawater or freshwater between oil hydrocarbon transfer operations.

Consequences

A sampling programme revealed significant marking of soil and underground water in the leak zone and downstream Clean-up operations began in 2020 and will continue at least into 2022. Several techniques for treating the polluted soil were retained and pumping and treating of underground water. The total cost of the operation was estimated at more than 800 k€.

The repair project, which is still pending validation by the community, is estimated at 1.8 M€. In the meantime, an alternative solution to unload the tanker by trucks was set up to supply the oil depot.

If the feed piping is overhauled, the operator plans to modify its operating methods, particularly by using nitrogen to inert the line between hydrocarbon transfer operations.