Hydrostadium

Hydrostadium, a fully-owned subsidiary of EDF, was entrusted with checking the resistance of the Pas-du-Loup hydropower plant in Arles-sur-Tech (France). The plant, which was refurbished in 1960, is supplied with water from an dam by a 120-metre long penstock. After inspecting the civil engineering of the facility, the penstock which connects the dam to the plant had to be inspected. “We naturally called on Cetim because a previous investigation carried out by Cetim’s experts had proven fully satisfactory” stated Yann Fage, civil engineer at Hydrostadium. Cetim’s experts carried out their investigation during a scheduled shutdown of the plant. They firstly performed a visual inspection inside the penstock. It was quite an acrobatic feat given that the penstock measures 1.3 metres in diameter. Rope access technicians were called in to support them in the very steep sections. 

A whole range of skills 

The second operation involved measuring from the outside, the residual thickness of the metallic wall and the pipe paint thickness every 6 metres. A conventional ultrasonic testing method was sufficient for this purpose. However, the phased array ultrasonic technique was preferred on the sections that had been previously identified as being potentially corroded. In fact, by using this technique which is similar to ultrasonography, the steel sheet thickness can be viewed over a surface area of 10 cm x 10 cm. The final operation, the examination of the welds at the area where the penstock branches off into three sections, required the use of three different types of tests (TOFD, ACFM and phased array testing) since the characteristics of the welds performed more than 50 years ago, are no longer documented. In the end, the structure was found to be in good condition.