2007 Volume 56 Issue 7 Pages 309-313
Flat healds (13Cr stainless steel, 340 mml×2 mmw×0.3 mmt) used in a water jet loom (WJL) suffer from crevice corrosion in the tap water. In the present work, a repassivation method for determining the critical concentration of chloride ion, Cl−, for the growth of crevice corrosion, CR, CREV, was measured using the metal/metal-crevice of heald in NaCl solutions containing less than 40 mg/L Cl−. Optimum conditions of potential and current to grow crevice corrosion in the initiation stage (S1) and the growing stage (S2) before the repassivation stage (S3) were examined. A heald was cut into two pieces and then a metal/metal-crevice was formed by overlapping the two pieces. Crevice corrosion was initiated in the solution containing 500 mg/L Cl− by a potentiokinetic method in S1. When crevice corrosion was grown at 200 mV vs. SCE in S2 by a potentiostatic method, corrosion area expanded, and then the specimen with two pieces did not work as a creviced one. Then, crevice corrosion in S2 was grown using a galvanostatic method with a current of 200 μA. Before changing to S3, the potential of specimen was raised up to a potential that was 50 mV lower than the holding potential in S3 by diluting test solution. Increases in current were observed after two times of dilution of the test solution in S3. CR, CREV was determined as the highest Cl− concentration in diluted test solutions in which no increase in current was observed. Use of galvanostatic method for growing crevice corrosion was desirable in the repassivation method of determination of the CR, CREV, because the quantity of electricity was controlled easily by time. The determined CR, CREV vs. potential relationship coincided well with the extrapolation line of the reported ER, CREV (repassivation potential for crevice corrosion) vs. Cl− concentration relationship in the tap water.
