The increasing cost of and demand for electrical energy requires a greater availability of generating plants including hydropower and pumped storage plants. Any improvement in materials, which will reduce the frequency and time of repairs to hydraulic machines and structures resulting from damage such as cavitation, can result in substantial savings. This research concerns the use of coating systems, which are suitable for the protection of the surfaces of hydraulic machines and structures. In this investigation the analysis was carried out for a turbine having a head of 500 m. However, the conclusions can be applied to the repair of any hydraulic machine or structure, which is subjected to erosion damage. Damage to the components (by corrosion, erosion and cavitation erosion) usually causes major problems and defects in hydraulic machinery, with respect to operation and maintenance. Cavitation erosion is the most usual damage, and the most troublesome. The number of machines subjected to this effect increases coninuously, owing to progressive growth of turbine design velocities and working loads. Not only machines such as water turbines and pumps (subjected to cavitation damage) but likewise parts of hydraulic nozzles, valves, distributors etc are af fected.

Several coatings have been found to be superior based on their overall performance in both cavitation tests and mechanical and interface properties tests. Polyurethanes for example are known to provide superior resistance to cavitation. A basic problem is however the adhesion strength of the coating to the surface of the substrate. In this research comprehensive material properties tests including compressive strength, flexural strength, tensile strength and elastic modulus were performed on selected coating materials. In addition to the available material properties tests different types of butt joint tests and shear box and single lap-joint tests were proposed to find the bond strength at the interface for six different polymeric coatings at an ambient curing regime. The result of materials characteristics and failure mechanisms were used as the basis for subsequent theoretical analysis. Interlocking techniques are proposed to increase joint strengths in tension and to reduce shear and peeling stresses at the interface.

A rigid epoxy resin and a rigid polyurethane were analysed using finite element methods to determine the interface stresses under different positions of hydraulic loads. In addition finite element analysis was used to predict the peel strength at the interface in a single lap joint test. Rigid polyurethane and epoxy resin based materials were used on site to protect the turbine runner blade and other parts of the hydraulic machinery against cavitation over damaged areas at Dinorwig and Ffestiniog power stations. So far it has been reported that all applications carried out on carbon steel have been successful. Based on the results of this research, and similar work, a relative constitutive procedure was suggested for predicting the behaviour of a protective coating under the action of a hydraulic load.