CHEMICAL ASPECTS OF STRESS CORROSION CRACKING OF AISI 321 STAINLESS STEEL IN HOT AQUEOUS CHLORIDE SOLUTIONS

摘要

The characterization as well as the description of corrosion defects on heat transfer tubes of nuclear power stations reflect wide field of chloride induced corrosion modes. Chloride induced cracks start from both the bottom of pits or the outer tube surface directly. The crack propagation is based on hydrogen embrittlement. The hydrogen is generated cathodically inside of pits and cracks. The initiation and propagation of cracks depend on both the kind and concentration of oxidants and anions. Oxidant increase the corrosion potential U_(corr) whereas special anions like chloride decrease the initiation potential of SCC. If U_(corr) > U_(scc). Crack initiation occurs depending on the Stress conditions.The erosion of cracks by corrosion depends strongly on temperature, pH, concentration of anions (electrolytic conductivity) and also on corrosion products formed inside the cracks. The corrosion and formation of solid corrosion products cause chemical blunting and plugging of cracks. The correlation of influencing chemical factors on initiation, propagation, blunting and plugging of cracks will be discussed with respect to crack arrest and restart during the Stress corrosion cracking processes.