Evaluation of Corrosion Property for Repair Welding Zone of Exhaust Valve

Abstract:

The diesel engine in the merchant ship is being operated in severe environment more and more because temperature of exhaust gas of combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality as the oil price is significantly being jumped for recent some years. As a result, the degree of wear and corrosion in between spindle and seat ring of exhaust valve are more particularly serious compared to the other parts of the engine. Thus the repair weld to the spindle and the seat ring is a unique method to prolong the life of the exhaust valve in an economical point of view. In this study, corrosion property of both weld metal and base metal was investigated with some electrochemical methods in natural sea water solution, in case of being welded with some welding methods and welding materials to the exhaust valve specimen as the base metal. In all cases, corrosion resistance of the weld metal was considerably superior to the base metal. In particular the weld metal of A2F(AC Shielded Metal Arc Welding with two pass by foreign electrode) showed a relatively good corrosion resistance compared to the other weld metals Furthermore pitting was somewhat observed at the corroded surface of the base metal while there was no its phenomenon on the surface of the weld metal.