Prediction of Tube-Tubesheet Galvanic Corrosion Using Finite Element and Wagner Number Analyses

Abstract

Galvanic corrosion predictions for heat exchanger tube/tubesheet galvanic couples are presented and discussed. The predictions were performed using finite element analysis using two programs, WECAN and MARC, and by Wagner number analysis under conditions of secondary and tertiary current distribution. Long-term electrochemical potentiostatic polarization data generated over 120 days in natural seawater were used to account for time effects. Results of the predictions are presented in the form of potential and galvanic current density as a function of distance from the tubesheet along the tube axis. Seawater exposures of some tube/tubesheet material combinations were performed to compare with the predictions. These exposures used segmented tubes connected in series through the use of zero resistance ammeters. Material combinations exposed included a Monel Alloy 400 tubesheet coupled to a 90-10 copper-nickel tube, a 90-10 copper-nickel tube coupled to a zinc anode at the position of the tubesheet, and a nickel-aluminum-bronze tubesheet coupled to an Alloy 625 tube. Tube/tubesheet data obtained from the literature were also compared to predictions. This study is directed towards determining not only the degree of accuracy of the predictions from the finite element and Wagner number analysis techniques, but also the sensitivity of the analyses to small changes in the electrochemical data used to obtain the predictions. The feasibility of these two analysis techniques for accurate qualitative as well as quantitative galvanic corrosion prediction for the tube/tubesheet configuration is discussed.

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Identifiers

DOI

10.1520/stp26195s

Journal

Galvanic Corrosion

Year

1988