Pitting Corrosion of Stainless Steel by Potable Municipal Water in an Organic Chemical Plant

Several tubes in a 35 m² (115 ft²) type 316 stainless steel shell-and-tube condenser leaked unexpectedly in an organic chemical plant that produces vinyl acetate monomer. Leaks were discovered after 5 years of operation and relocation of the condenser to another unit in the same plant. Examination of tubes and tube sheets revealed pitting damage on the OD surface. Some of the pits had penetrated fully, resulting in holes. Inside diameter surfaces were free of corrosion. Macro- and microexaminations indicated that the tubes had been properly manufactured. Pitting was attributed to stagnant water on the shell side. It was recommended that the surfaces not be kept in contacts with closed stagnant water for appreciable lengths of time.