(153f) Galvanic Corrosion Between Dissimilar Metals

A Dow USGC cracker suffered a tube failure on a cracked gas compressor inner stage cooler after ten plus years of service.  To further extend the equipment life, the decision was made to replace the tube bundle and upgrade the metallurgy of the tubes from admiralty brass to Duplex stainless steel.  The new tube bundle was placed in service, but failed after only eight months of operation.  The premature failure was found to be caused by deep pitting in the carbon steel tubesheet.  The dissimilar metals of the Duplex tubes and carbon steel tubesheet, with river water acting as the electrolyte, formed a galvanic cell which preferentially corroded the carbon steel tubesheet.  This paper will describe the details of the failure and failure mechanism.