Spillway at hydropower station restored despite three floodings

At a run-of-river Hydro Plant in France, the spillway on a Kaplan turbine was repaired and protected in situ with a combination of epoxy composite and coating systems. Despite three flooding events occurring during the repair procedure, the application team was able to overcome this, successfully repairing the spillway and protecting it against future erosion and corrosion damage for the long term.

The Hydropower Station was experiencing generalised erosion and corrosion, covering approximately 40 sq metres on one of its spillways with 15mm metal loss recorded in some areas. This was caused by continuous exposure to high-velocity water, turbulence and abrasive particles. An intervention was required in order to rebuild the damaged profiles, restore hydraulic geometry and provide long-term protection against further wear in this challenging environment.

The Plant produces almost two billion kWh of electricity per year - enough to supply roughly 815,000 households with electricity annually. Given the critical role the plant plays in providing renewable energy to the local area, it was imperative that the application was carried out promptly, with minimum downtime being incurred.

Specification of epoxy repair composite and protective coating

Following an inspection by authorised Belzona distributor, Protecmo, a combination of epoxy coating and composite systems were specified.

For the severely corroded and eroded areas, Belzona 1311 (Ceramic Metal) was chosen. This is a 100%-solids, ceramic-filled epoxy repair composite, specifically designed to repair metal surfaces subjected to high levels of erosion and corrosion. Following a successful erosion resistance test carried out by the Client, the epoxy coating, Belzona 1331, was further specified. This system will provide outstanding erosion and corrosion resistance under immersed conditions, such as those found in the aqueous environment of the spillway.

As this polymeric technology is cold curing, this helps to mitigate the health and safety concerns that can otherwise arise when hot work is involved.

Application team adapt to unexpected flooding

Firstly, a fully sealed containment airlock was installed; incorporating air treatment, dust extraction and vacuum recovery systems to ensure safe and controlled working conditions.

All surfaces were then grit-blasted using corundum abrasive to provide a surface compliant with Sa 2.5 cleanliness in accordance with ISO 8501-1. Unfortunately, three flooding events occurred during the surface preparation stage. In order to adapt to these unforeseen events, the team had to grit-blast the substrate three times.

In areas with material losses of up to 15 mm, custom-made formers were used to apply the two-part system, Belzona 1311 (Ceramic Metal). This technique ensured that the substrate could be accurately restored to its original hydraulic profile.

The two-part epoxy coating, Belzona 1331, was then applied in two coats of approximately 300 um each, achieving a minimum total dry film thickness of 600 um.

Throughout the application process, careful control of material impregnation, overcoating intervals and curing times and conditions was maintained to ensure the long-term durability of the repair.

The combination of Belzona systems, combined with an efficient and adaptive application carried out by Protecmo's team, ensured that the spillway was successfully repaired and protected against future damage with minimum downtime being incurred. In turn, by prolonging the lifespan of this critical hydropower asset, this supports the Hydropower Station's contribution to renewable energy generation.