Pollution
Humain
Environnement
Economique

A natural gas pipeline burst at around 10 a.m. at an underground natural gas storage site. The personnel stopped the gas transfer operations in progress from the manifold to the storage well. Access to the area was prohibited, and explosimetry measurements were performed. The Inspection Authorities of Classified Facilities arrived on site in mid-afternoon.

The structure in question measured 1 km in length and was commissioned in 1976. It has an operating pressure of 67.7 bar (tested at 102 bar) and measures 219 mm in diameter. The piping is protected by a coal tar pitch coating. Registered in the ‘guichet unique’ (the gas utility’s web portal), the gas line is buried at a depth of 1 m and passes through public land over 2/3 of its route. It is monitored by the site’s internal inspection department in the scope of the monitoring program (monitoring of the cathodic protection).

At the time of the accident, the pipe was in a gradual restart phase with step-by-step pressure build-up. The rupture occurred at 34 bar, at a 90° elbow toward the wellhead, when the pipeline pressure was increasing at a speed of 0.5 bar/s. The blast created a crater measuring 4 m in diameter and 1.5 m deep. Soil was thrown over several tens of metres.

No trace of combustion or explosion was noted, and no work had been in progress in the vicinity. Samples were taken on the defective section for metallurgical analysis. The expert assessment concluded that the rupture was not the result of metallurgical degradation (corrosion, fatigue, erosion due to sand drainage, etc.), but rather a “sudden ductile fracture”.

Following the event, the administration asked the operator to have a third-party expert evaluation conducted on the causes of the accident, on the calibration certificate of the pressure gauges used for the transfer operations and a summary of the inspections conducted on the structure and their results.