Failure investigation of Muntz tubesheet and Ti tubes of surface condenser

Failure investigation was carried out on corroded Muntz tubesheet and Ti tubes of a surface condenser. The Muntz metal was found to have suffered from corrosion grooves and micropits, which were crystallographic in nature. X-ray mapping revealed the occurrence of dezincification. The Ti tube ends suffered from separation and cracking of the deformed grains in addition to shallow localized attack. Corrosion of the Muntz metal was attributed to coupling with Ti, while corrosion of Ti was due to formation of Ti-hydride as a result of the utilization of sacrificial Al anodes in the waterbox. Seasonal variations in seawater temperature and proximity of Ti tube ends to waterbox anodes may have aided hydriding of the Ti tubes. Recommendations were given to discontinue the application of sacrificial cathodic protection and to epoxy coat the cast iron waterbox and the Muntz tubesheets.