Detection of crevice corrosion by optical interferometry

In the present investigation, an optical corrosion-meter has been developed for materials testing and evaluation of different corrosion phenomena. The idea of the optical corrosion-meter was established based on principles of 3D-holographic interferometry for measuring microsurface dissolution, i.e, mass loss, and on those of electrochemistry for measuring the bull; electr onic current, i.e. corrosion current of metallic samples in aqueous solutio ns. In the present study, an early stage of crevice corrosion of a stainles s steel and a carbon steel in seawater was monitored in situ by the optical corrosion-meter during the cyclic polarization test. The observations of c revice corrosion were basically interferometric perturbations detected only on the surface of the carbon steel underneath a crevice assembly, made of Teflon bolt, Teflon nut, and Teflon washer. The interferometric perturbatio ns interpreted as a localized corrosion in a form of an early crevice corro sion of a depth ranged between 0.3 mu m to several micrometers. On the othe r hand, observations of uniform fringe patterns were detected on the sample of the stainless steel indicating that the stainless steel sample was subj ected only to uniform (general) corrosion attack during the cyclic polariza tion test. Consequently, results of the present work indicate that holograp hic interferometry is a very useful technique as a 3D-interferometric micro scope for monitoring crevice corrosion at the initiation stage of the pheno menon for different metallic samples in aqueous solutions. (C) 2000 Elsevie r Science Ltd. All rights reserved.