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Alloy Cu-10% Ni (ASTM B-111, UNS C70600) has been used extensively for condenser and heat exchanger tubes in power stations. However, there have been cases of severe localized corrosion in this alloy. This paper presents the evaluation of Cu-10% Ni in a dynamic online monitoring system with oneway circulation using alkaline (pH 7.2 to pH 8.8) brackish water with and without chlorination for 3-, 8-, and 12-month exposure periods. Electrochemical laboratory tests-opencircuit potential (OCP), linear polarization resistance (LPR), and cyclic polarization (CP)-also were run. Before chlorination, the microbiological water analysis indicated microbial development with planktonic and sessile sulfate-reducing bacteria (SRB) on the order of 10 7 cells/mL and 10 5 cells/mL, respectively, with sessile SRB at 10 cells/mL after chlorina- tion. Prechlorination scanning electron microscopy (SEM)/ energy dispersive x-ray (EDX) analysis/x-ray diffraction (XRD) analysis after 3 months revealed very few cuprite (Cu 2 O) crystals and bacterial cells, whereas dense cell populations associated with hemispheric holes typical of microbiologically influenced corrosion (MIC) were found after 8 months. Postchlorination SEM/EDX/XRD analysis helped establish a definition of how chlorine increases the Cu-10%Ni corrosion rate. Initially, a dense layer of star-shaped Cu 2 O crystals was observed. It later was removed partly because it quickly oxidized into nonprotective, nonadherent secondary corrosion products, which again exposed the material to the hypochlorite ions in the corrosive medium, consequently forming a new layer of Cu 2 O. The formation of different corrosion products and redeposited copper with severe localized corrosion below the deposits and severe general corrosion finally were shown by the analysis of a tube that was in service for 3 years in the same chlorinated, brackish water. CP curves indicated that chlorine content increased the corrosion current from 2.5 µA/cm 2 per 0.0 ppm Cl 2 to 5.0 µA/cm 2 per 0.3 ppm Cl 2 , and that Cu-10% Ni is not passivated in this brackish water. All these results suggest that this alloy is not corrosion resistant in brackish water, and chlorine treatment accelerates corrosion even more.

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The mechanism of microbiologically infl uenced corrosion (MIC) on carbon steel (CS) by the bacteria Desulfovibrio desulfuricans subs. desulfuricans was studied using hydrogen permeation, open-circuit potential, and cathodic polarization techniques, in a concentrated culture medium containing bacteria cells (10 7 cell/mL) and ferrous ions (300 mg/L) designed to simulate a condition common in systems for the secondary recovery of crude oil, characterized by highly contaminated microenvironments that severely corrode iron alloys in a short time period. This research project was carried out using several 24-h experiments to defi ne initial stages of the corrosive process under the conditions indicated. The results evidenced a hydrogen permeation current peak of about 12 µA correlated with a minimum open-circuit potential of -780 mV vs saturated calomel electrode (SCE), 400 min after inoculation. Next, the permeation current decreased abruptly to its base line and the potential increased, stabilizing at -585 mV SCE at 24 h, a condition that is associated with high, similar bacterial activity both with and without cathodic polarization (10 8 CFU/mL and 10 9 CFU/mL), typical hydrogen sulfi de (H 2 S) attack morphology, and a weak iron sulfi de fi lm. These results using CS as the corrodible material, together with those obtained using a palladium strip as previously reported, show defi nitely that the cathodic depolarization theory does not represent the chief mechanism used by D. desulfuricans in the MIC process, whereas sulfi de corrosion together with iron sulfi de products seem to better explain the mechanism of this severe bacterial corrosion problem.KEY WORDS: biofi lms, carbon steel, cathodic depolarization, Desulfovibrio desulfuricans, hydrogen permeation, microbiologically infl uenced corrosion, sulfate-reducing bacteria, sulfi de corrosion

Exotic marine organisms, Garveia Franciscana, called “Pelo de Oso” by the locals, were detected in Lake Maracaibo. “Pelo de Oso” constitutes one of the three components of the metal/biota/solution system that interact in Lake Maracaibo, producing biofouling and microbiological corrosion. The latter generates great economic problems, mainly: water‐pump failures. The objective of this paper was to determine the preference of these bioorganisms for materials, when immersed in Lake Maracaibo.