MIC Problems in a Seawater Cooling Water System on Coated CS and 70-30 Cu-Ni

Abstract Seawater from the Gulf of Mexico is used as the Cooling Water (CW) makeup for a large industrial production plant and is cycled about 1.25-1.75 times in an open recirculating cooling tower. About five months after startup, leaks were found in internally coated Carbon Steel (CS) piping and equipment, as well as in 70-30 Cu-Ni condenser tubing. The leaks were attributed to Microbiologically Influenced Corrosion (MIC) resulting from inadequate biocide treatment and stagnant conditions during the plant startup and early runs. Evidence was found that the MIC was very aggressive at any coating defects, including defects that would pass the coating inspection criteria. Titanium condenser tubing in the same plant showed the presence of bacteria growth but did not suffer corrosion. The mitigation steps involved extensive cleaning of the system using mechanical and chemical treatments, repeated flushing, and improved biocide treatment. Some areas of thinned piping were replaced, and others were externally wrapped with fiberglass. Numerous condenser tubes were plugged, and some condensers were retubed.