Masters Theses

Date of Award

8-1998

Degree Type

Thesis

Degree Name

Master of Science

Major

Metallurgical Engineering

Major Professor

R. A. Buchanan

Committee Members

Charlie R. Brooks, Anthony J. Pedraza

Abstract

An abiotic laboratory screening test (ALST) was developed that replicated the major corrosion-causing characteristics of several natural biotic environments. The natural biotic environments replicated were a Delaware Bay seawater site, an Arizona well-water system and a Tennessee River fresh-water system. The ALST was designed to produce the following major microbial effects with respect to corrosion: (a) the high oxidizing power of the natural environment, (b) the chloride concentration of the natural environment, and (c) aerobic and anaerobic areas on the specimen surface, as produced by colonies of aerobic and anaerobic microorganisms in the natural biotic environment. The ALST was evaluated by conducting corrosion tests on various materials (platinum electrodes, alloy 400, AL-6XN alloy, and 304L/316L stainless steels). The results obtained were compared with those obtained from the field studies at the natural biotic environment sites. It was found from polarization resistance measurements in the abiotic solution that alloy 400 had a corrosion rate that was in good agreement with that obtained in the Delaware Bay natural biotic water environment. Cathodic polarization behaviors were determined for platinum electrodes, alloy 400, and 304L stainless steel in the abiotic solution. Comparison of these results to those obtained in the field studies in the natural environments showed that the corrosion current densities were somewhat higher in the abiotic solution.

The open-circuit potentials (OCP) obtained for the materials in the abiotic solution were significantly higher than those obtained in the natural biotic environments. The visual and microscopic results of the surfaces of the weldments after exposure in the ALST compared favorably with their counter-parts after exposure in the natural biotic water environments.

From the results, the developed ALST replicated the natural environments reasonably well. The higher ennoblement and corrosion current densities obtained in the ALST are indications that the developed ALST is a conservative test. If there is no significant accelerated corrosion in the ALST, there will not be significant accelerated corrosion in the natural biotic environment; but if there is significant accelerated corrosion in the ALST, there may or may not be significant accelerated corrosion in the natural biotic environment.

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