Experience with Standard Duplex Stainless Steel Cooling Water Pump in Arabian Gulf Seawater Conditions

摘要

Corrosion problems can be a serious issue in seawater pumps because of the aggressive nature of seawater. Usually damage in seawater can be minimized through the use of highly corrosion resistant materials. Wrought UNS S31803 (S31803) and cast UNS J93372 (J93372) duplex stainless steels are frequently used in seawater pump construction because of their superior resistance to localized corrosion and higher strength compared to austenitic stainless steels which are a cheaper material option. Corrosion rates in chlorinated seawater depends on temperature and chloride content, among other operation factors. The higher chloride content and cooling seawater temperature on the Gulf coast presents corrosion challenges that are unique to the region which can make materials that perform well in typical cooling seawater systems to corrode under certain operating conditions. The failure of a vertical seawater cooling pump component, made up of S31803 and J93372 duplex stainless steels after less than two years of intermittent operation, is presented as an example of the poor performance of standard duplex stainless steels in Arabian Gulf cooling seawater. S31803 shaft enclosing tube stud bolts and nuts of a seawater pump were found to be severely corroded. Results of lab analysis, that includes optical microscopy, hardness testing and chemical analysis done are presented. Analysis of the failed nuts and bolt indicated that they suffered from crevice corrosion with both ferrite and austenite being preferentially attacked in different areas. Severe pitting of the UNS J93372 impeller was also observed on the same pump. Only superficial pitting was observed on the four pumps that were operating continuously on the same pond as the one that failed. This failure illustrates that UNS S31803 and S93372duplex stainless steels should be selected and used with care under the extreme gulf seawater conditions.