Intergranular stress corrosion cracking of nickel alloys in pressurized water

Failures of Alloy 600 and 800 secondary cycle steam generator tubes in Swiss and German nuclear reactors were attributed to design factors and water chemistry changes after operation times up to 14,000 h. A change in water treatment also is suspected as contributory in one plant. Examination of deposits indicated high caustic concentrations are a main factor in intergranular stress corrosion cracking of up to 20 percent of tubes in one plant. Laboratory tests on samples from failed tubes pointed to incipient H embrittlement after long exposure in 3000C water and metallurgical conditions similar to those found in material heat sensitized at higher temperatures