Corrosion Failure Analysis of a Heat Exchanger Tube Fed from Persian Gulf Water

Monel 400 is one of the most important nickel-based alloys which possesses high corrosion resistance, weldability and strength and is employed extensively in marine industries particularly in heat exchangers and boilers. It is generally used as tubes in water cooling systems especially where sea water is used as cooling water. In the current work, the causes of premature failure of a Monel heat exchanger tube of a water cooling system of an oil refinery in the south of Iran which is fed directly from Persian Gulf sea water were studied by means of different microscopical and analytical techniques. The results indicated the presence of sulfate and thiosulfate reducing bacteria as well as acid producing bacteria in the water entering the heat exchanger, in addition to formation of sulfide compounds on the internal surface of the tubes. Consequently, the main cause of failure of the tube was determined to be pitting corrosion which was dominantly initiated due to microorganisms in the sea water.