A leak was identified around 10:40 a.m. while grounds maintenance operations were being over a buried pipeline (DN 200, P 12 bar). The discharge of biodegradable water containing chemical effluents from a chemical plant, including carbon tetrachloride and toluene, polluted 30 tonnes of soil. The site’s internal contingency plan was initiated.

Consequences

The leaked impacted an area of 25 m². Piezometers were installed to monitor groundwater quality (one upstream of the leak and two downstream), as it was estimated that 2 m³ of the product was released. Soil samples were taken in order to estimate the degree of pollution.

Causes

Excavation operations revealed that the puncture had measured approximately 5 mm in diameter, and was located in the lower part of the tube. Internal corrosion of the pipe related to the quality of the effluents conveyed would be the cause. Losses in thickness were also observed at other points in the structure. The pipeline is thus now closely monitored by its operator: weekly inspections, bi-monthly thickness measurements, quarterly pressure test pending complete replacement.

Measures taken

The damaged section was replaced. Dye penetrant and ultrasonic inspections were conducted on the ends of the existing sections of the piping before welding. The splicing welds were also 100% x-rayed before being subjected to a pressure test at 10 bar. Other work is also planned on the rest of the remaining pipe run under the control of the SIR (Service d’Inspection Reconnu, recognised inspection department).