CORROSION SCIENCE SECTION CORROSION—Vol. 58, No. 10 863 0010-9312/02/000191/$5.00+$0.50/0 © 2002, NACE International Submitted for publication March 2001; in revised form, April 2002. * The Pennsylvania State University, The Department of Civil and Environmental Engineering, 212 Sackett Building, State College, PA. Use of Electrical Resistance Probes for Studying Microbiologically Influenced Corrosion R.A. Royer and R.F. Unz* ABSTRACT An experimental system was developed to study microbio- logically influenced corrosion (MIC) of metals under an anaerobic environment. The computer-interfaced process fa- cilitates near-real-time corrosion monitoring of many samples run in parallel. To validate the experimental approach, elec- trical resistance probes were monitored over time and the data were used to estimate the rate of corrosion and deter- mine if the corrosion was uniform over the probe surface. Corrosion rate estimates, determined from polarization mea- surements, were compared to those calculated from resis- tance increases under several experimental conditions. Time-to-failure for wire samples was also used to evaluate the nature of the corrosion. The relationship between resis- tance increase and time to failure was used as a possible indicator of localized corrosion. KEY WORDS: biocorrosion, electrical resistance probe, im- mersion testing, microbiologically influenced corrosion, non- destructive testing, sulfate reducing bacteria, sulfide stress cracking INTRODUCTION The analytical measure of biocorrosion or microbio- logically influenced corrosion (MIC) has typically involved the use of electrochemical (e.g., polarization, scanning vibrating electrode, linear polarization re- sistance 1-6 ) and physical (e.g., weight loss 7-12 ) meth- ods. Electrochemical test methods for MIC have been discussed previously. 13-14 Although these techniques have facilitated acquisition of much information, their use has not resolved the mechanisms of biocor- rosion. 15-16 The common corrosion monitoring/testing technique of utilizing electrical resistance probes has only seen minimal use in the study of MIC. 17 The introduction of a biological component to a corrosion study is likely to cause increased variabil- ity in the results but this may be offset by increased sampling and replication. Temporal heterogeneity is often a feature of biocorrosion that is difficult to es- tablish from “snap shots” of the system as obtained through weight-loss and destructive electrochemical methods. 7-10 The use of electrical resistance to measure corro- sion rate is well established, especially in corrosion monitoring and control. 18-23 Advances in technology have allowed a transition from periodic, manually ob- tained measurements to automated, near-real-time assessment of corrosion rates. 19,21,24-27 The investiga- tion of MIC, however, has seen little use of electrical resistance probes (ERP). 17 ERP are fundamentally simple, based upon an increase in resistance when a conductive sample of known initial geometry cor- rodes. Increases in resistance can be translated into a uniform corrosion rate, with results comparable to other techniques that “assume” uniform corrosion. ERP offer some advantages and disadvantages rela- tive to more advanced electrochemical techniques and simple weight-loss measurements. Among the primary advantages of ERP is the ability to collect successive data on precisely the