STRESS-CORROSION CRACKING BEHAVIOR OF STAINLESS-STEELS WITH RESPECT TO THEIR USE IN ARCHITECTURE .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 us e in arcitecture. A preceding paper presented investigations into stre ss corrosion cracking (SCC) in the active state of corrosion; the pres ent paper deals with SCC in the passive state. The investigations show ed that - in contrast to general opinion - stress corrosion cracking i n the passive state can occur at temperatures well below 50-degrees-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 s tress level, pH value or type of kation only exert a subordinate influ ence. Especially the high alloy austenitic steels 1.4439 and 1.4539 pr oved SCC-resistant under such conditions at ambient temperatures. Elec trolytes with critical chloride concentrations may develop when deposi ts containing chlorides of sufficiently high solubility (e.g. MgCl2, C aCl2) are exposed to an atmoshere with critical, i.e. comparatively lo w humidity. Such conditions are evidently met only under very specific circumstances such as may occur in indoor swimming pools. In other st ructures where stainless steels have been used for decades without suc h damage having occurred to date, these critical conditions appear gen erally not to be reached.