A resistance-welded carbon steel superheater tube made to ASME SA-276 specifications failed by pitting corrosion and subsequent perforation, which caused the tube to leak. The perforation was found to have occurred at a low point in a bend near the superheater outlet header. It was found that the low points of the superheater tubes could not be completely drained during idle periods. Water-level marks were noticed on the inside surface above the area of pitting. It was revealed by microscopic examination that localized pitting had resulted from oxidation. It was concluded that water contained in the tube during shutdowns had accumulated and cumulative damage due to oxygen pitting resulted in perforation of one of the tubes. Filling the system with condensate or with treated boiler water was suggested as a corrective action. Alkalinity was suggested to be maintained at a pH of 9.0 and 200 ppm of sodium sulfite should be added to the water.

A residential subdivision near Tampa, FL was constructed in 1984 through 1985. Several sections of copper pipe were removed from one residence that had reported severe leaking. Visual examination revealed extensive pitting corrosion throughout the ID surfaces of the sample. Microscopic evaluation of a cross section of a copper pipe revealed extensive pitting corrosion throughout the inner diametral surfaces of the pipe. Some pits had penetrated through the wall thickness, causing the pin hole leaks. Analysis of a sample of water obtained from the subdivision revealed relatively high hardness levels (210 mg/l), high levels of sulfate ions (55 mg/l), a pH of 7.6 and a sulfate-to-chloride ratio of 3:1. Analysis of corrosion product removed from the ID surfaces of the pipe section revealed that an environment rich in carbonates existed inside the pipe, a result of the hard water supply. It was concluded that pitting corrosion was a result of the corrosive waters supplied by the local water utility. Waters could be rendered non-pitting by increasing their pH to 8 or higher and neutralizing the free carbon dioxide.