Acoustic Emission and Potential Fluctuation During Chloride SCC with Oxide in Its Surface
Akio YONEZU, Yoshiro TANIYAMA, Hideo CHO, Takeshi OGAWA and Mikio TAKEMOTO
Abstract:Both the acoustic emission (AE) and corrosion potential fluctuation were monitored for chloride SCC of sensitized Type-304 steel plate under bi-axial stress state. Branched SCCs were produced from rectangular-shaped corrosion pits initiated by falling-off of surface grains and filled with chromium oxide in 30mass% MgCl2 solution (363K). Both the AE and potential fluctuation were simultaneously detected at corrosion pit formation and SCC propagation. Two types of AE (Type-I and Type-II) were monitored. Type-I Aes with higher frequency components were detected during the pit growth and supposed to be produced by falling-off of surface grains due to intergranular attack, while a number of Type-II Aes (about 12,500 counts) with low frequency components were detected at SCC progression and supposed to be produced by cracking of the oxides. Though the Aes detected during SCC test are not the primarily signals from the SCC itself, secondary AE can be usefully utilized to monitor the SCC initiation and propagation as well as the corrosion potential fluctuation. Key Words:Type-304 stainless steel, Chloride-SCC, Bi-axial stress state, Lamb wave AE, Corrosion potential, Falling off of grain, Oxide fracture