"corrosion of air/brackish water cooler"
"The temperature of the control room of a coal and iron ore terminal, located near the coast, is controlled by circuling air through a 316 heat exchanger, of which the secundairy circuit consisits of brackish water pumped to and from the port. The wet part of the cooler is heavily pitted and leaking after 1 year of service, mostly at welds, the dry surface shows small pits of .1 to .2 mm deep). The cooler has a built in CP with zinc anodes which look OK. For wet surface corrosion I think of (1) wrong material for brackish water, (2) stray current between electric ground and port, (3) coal particle deposits. For the dry surface pitting I think of coal or iron particle deposits. Could you please comment on possible causes?"
You might consider chlorides in the brackish water. They are known pitting agents of the 300-series stainless steels.
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