Inspection of a seawater cooled plate heat exchanger of 254 SMO in the Naantali power station

Plate heat exchanger plates of the high-alloy stainless steel 254 SMO with 6% Mo has after just over five months of operation been penetrated (0,7 mm) by crevice corrosion both under rubber gaskets and at points of contact between adjacent plates. The heat exchanger has been used for cooling of oil at max 50 degrees C with Baltic water (3400 mg Cl-/1, max 30 degrees C). In another identical heat exchanger in which freshwater at max 35 degress C has been cooled with the same brackish water, in this case heated to max 25 degrees C, no crevice corrosion has been observed after just over two years of operation. No other reason why corrosion occurred in the former, but not in the latter case than the difference in operating temperature has been demonstrable. (author)