Repair of a penstock
OIKEN hired HYDRO Exploitation to carry out repair work on a penstock. A water leak had been detected during a video inspection by HYDRO in October 2022.
The penstock is located in an unstable area; consequently, the concrete blocks that support it are prone to moving. That is why OIKEN plans to replace it in 2026. In the meantime, the company would like a temporary solution for the interim of three years.
A section of the penstock to be renewed in steel
As a first step, the welding team was asked to carry out an expert assessment of the defective area and submit a solution for its repair. After chipping away at the concrete around the water leak, an appraisal of the cracks revealed that the material was excessively elongated, i.e. exceeded its elastic limit, as a result of the displacement of the concrete. Our specialists proposed replacing the weakened area with a two-metre section of 6-mm thick S355 steel. To accommodate the elongation of the penstock in the new section and not the concrete part, a metal ring was added to the downstream part of the piece, and sealed in the concrete. This ensures the area can endure stress loading again.
Cutting, inserting, welding and painting
To honour both the deadline and the expected level of quality, the ferrule was welded at our workshops in Martigny, while the on-site work was entrusted to our mobile welding team. Given the penstock is subject to heavy stresses, one of our specialists cut the section using a blowtorch. During the procedure, the penstock gave way and moved back approximately ten centimetres – an observation confirmed by our expert assessment. Once the area was cleared, the new section could be inserted, despite the ovaling of a part of the penstock and the challenging working conditions due to the inclement weather and hampered access. Our mobile team was nevertheless able to find solutions and guarantee welds that comply with the radiographic and magnetic testing criteria. The Martigny painting team was then able carry out the alterations on the outer part of the piece once the welds were validated. The penstock could be put back into operation in the water, approximately 48 hours after we left the site.
