Stress corrosion cracking behaviour of stainless steels with respect to their use in architecture,part 2: corrosion in the passive state

Unexpected failures of 18/10 CrNi and 17/12/2 CrNiMo steels in indoor swimming pool atmospheres made it necessary to reinvestigate chloride stress corrosion cracking of stainless steels with respect to their use in arcitecture. A preceding paper presented inwestigations into stress corrosion cracking (SCC) in the active state of corrosion; the present paper deals with SCC In the passive state. The investigations showed that – in contrast to general opinion – stress corrosion cracking in the passive state can occur at temperatures well below 50°C in 18/10 CrNi and 17/12/2 CrNiMo steels, provided the corrosive medium has an extremely high chloride concentration. Other factors such as stress level, pH value or type of kation only exert a subordinate influence. Especially the high alloy austenitic steels 1.4439 and 1.4539 proved SCC-resistant under such conditions at ambient temperatures. Electrolytes with critical chloride concentrations may develop when deposits containing chlorides of sufficiently high solubility (e.g. MgCI₂, CaCl₂) are exposed to an atmoshere with critical, i.e. comparatively low humidity. Such conditions are evidently met only under very specific circumstances such as may occur in indoor swimming pools. In other structures where stainless steels have been used for decades without such damage having occurred to date, these critical conditions appear generally not to be reached.