1993 Volume 42 Issue 1 Pages 20-26
Premature leakage of hot water was found for Type 304 steel tube. Most cracks started from the inner surface of the tube in contact with 60°C water containing 2 to 4ppm Cl-. A 304 tube, which had been used for several years and had thick film, showed markedly noble spontaneous potential, ESP, of 156mV vs. SCE at one day and later of 236mV, which could be atributed to residual chlorine injected into the water originally before heating. A specimen cut from the failured tube showed a pitting potential, V′C, less noble than 200mV. Such values of V′C lower than ESP were reproduced with 304 steel specimen which had been cold-rolled up to 66% and had martensite introduced. It was concluded that anodic dissolution started in a form of pitting at the martensite phase in the cold-rolled 304 tube in the highly oxidizing water and then developed into stress corrosion cracking under residual stress and the temperature higher than 50°C, critical one for Type 304 steel. Presented countermeaures are ensurement of solution-treatment for 304 steel tubing or use of Type 316 in place of Type 304.
