2007 Volume 61 Issue 3 Pages 155-158
Acoustic Emission (AE) technique becomes a useful tool to monitor local corrosions. It utilizes AEs produced by fracture of corrosion product (rust) and hydrogen gas evolution. In case of SCC associated with pitting corrosion of Type-304 stainless steel in concentrated chloride solution, AEs were produced by the oxide fracture in the pits prior to the SCC initiation. Detected AEs could be classified into two types (Type-I and-II) by their frequency characteristic. Type-II with low frequency components less than 0.2 MHz was found to be produced by the rust fracture while the Type-I by the mechanical fall-off of grains. Crevice corrosion test of flange-connected Type 304 steel pipe in 3 and 20 mass% NaCL solutions at controlled potentials produced frequent AEs. Generation rate of the AE was found to be proportional to the anodic current or the progression rate of the crevice corrosion. A new AE system utilizing telecommunication optical fiber was demonstrated to detect AEs from the rust fracture and expected to be a low-cost monitoring system applicable to large process equipments.
