Small amounts of chloride in secondary pressurized water reactor (PWR) or primary boiling water reactor (BWR) water-steam circuits can cause stress corrosion cracking (SCC) of stainless steels. Important factors are

• local environment (oxygen content, chloride content, and pH value),
• steel composition and structure (welds),
• internal strain
• temperature.

Constant extension rate test experiments have been performed on AISI 304 at 200°C in a 0.001 M NaCI solution. During straining, the specimens were kept at constant potentials in the range of -400 to +425 normal hydrogen electrode. Chloride SCC was seen only at potentials above +150 mV NHE.

At lower potentials, only small brittle surface cracks were formed, because slow straining at high stress levels strengthens the steel. From corrosion potential measurements at 200°C in oxygen-containing water, it follows that the critical potential value of + 150 mV NHE can be reached with oxygen contents above 10 ppb in nearly stagnant water.