Microbiologically Influenced Corrosion of Galvanized Steel by a Metalworking Lube
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CASE HISTORY—PEER-REVIEWED
Microbiologically Influenced Corrosion of Galvanized Steel by a Metalworking Lube Ganiyu A. Jaiyeola
Submitted: 24 August 2012 / in revised form: 12 December 2012 / Published online: 16 January 2013 ASM International 2013
Abstract This article investigated the corrosion failure of galvanized steel that had been exposed to a metalworking lube. The investigation included metallographic preparation (sectioning, mounting, and polishing), microstructural analysis, optical microscopy, zinc coating thickness measurements, fluid pH measurements, microbiological testing, and Fourier Transform InfraRed spectroscopy. The results from this investigation showed that the failure that occurred was due to microbial corrosion. Keywords Bacterial corrosion Coating thickness Corrosion failure analysis Introduction Microbiologically Influenced Corrosion (MIC) [1–6] is corrosion that occurs as a result of biological activities of microbes (bacteria, fungi, algae, etc). Microbes form biofilms on alloys and polymer surfaces, which enable them to corrode those surfaces. MIC occurs mainly because of the corrosive chemicals that microbes generate from their biological activities. Microbes are very resilient. The following properties of microbes foster MIC: • •
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Microbes can survive from 12 to 110 C Microbes can tolerate a wide range of pH, salinity, and pressure values provided that nutrients are available to an extent [10 mg/l Some microbes can survive in environments containing more than 2 mg/l of free chlorine [7]
G. A. Jaiyeola (&) Element Materials Technology, 51229 Century Court, Wixom, MI 48393, USA e-mail: [email protected]
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This case study failure analysis involved an electrogalvanized steel tub that corroded. The steel emitted a foul smell after it was sprayed with a diluted metalworking lube (2:1; fresh lube to deionized water). The first step in the steel processing was rubbing with oil (containing a rust preventive), followed by spraying with the diluted lube. The lube delivery system consisted of fresh lube in drums flowing into a drum for dilution, and subsequent spraying of the diluted lube onto the steel. A backup to the fresh lube drum is a makeup drum that is connected directly to the dilution drum. The lube from the makeup drum flows into the dilution drum whenever the fresh lube drum is depleted. The makeup drum is very rarely used or cleaned out for months or even years since fresh lube drums are routinely replacing empty fresh lube drums. Essentially, the makeup drum serves emergency situations when the plant is out of supplies of fresh lube drums. The plant had a log for ordering fresh lube drums before supplies were consumed. However, no log was available for preventive maintenance of the makeup drum. Therefore, there was no record of the last time when the makeup drum was cleaned or fresh lube was added. Thus, the potential that bacteria could form and grow in the makeup drum was quite possible due to the extended time the makeup drum was cleaned. After the rash
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