Corrosion Behavior of Welded Repaires for Water Turbine Blades

Abstract

The immersed components of hydroelectric power plants are permanently in contact with the water stream and their wear occurs by corrosion, erosion and cavitation. This damage is usually repaired by welding: the procedure is fast and reduces plant downtime. Adopting proper weld procedures are crucial for blade performance and to establish a protocol the following experiment was devised: rectangular samples 600x200x15mm were obtained from a discarded blade used in a hydroelectric power plant and in the median region a 3mm deep groove was milled to simulate erosion damage. The damage was repaired by welding using MIG, WIG, MMAW and oxyacetylene techniques using 136L as filler on cold and preheated at 400�C base materials. Specimens from the welded ensembles were obtained and prepared accordingly for corrosion testing. Post corrosion testing studies using the light microscope and scanning electron microscope were performed in order to determine surface damage. At first glance results appear contradictory: the corrosion test results revealed best behavior for MIG weld repairs, on the cold sample, while the corrosion features measured on the exposed area revealed that oxyacetylene welding would be best. Complementary methods are required and currently employed to establish optimum welding procedure parameters for water turbine blade repairs.