Effect of pH and temperature on the performance of zinc anodes for a risk-based storage tank management approach

摘要

Purpose - The purpose of this paper is to illustrate the complex nature of galvanic corrosion and how it is affected by various key factors related to material characteristics and material processing parameters. In particular, this study aims to explore the effect of pH and temperature on the integrity of a system galvanically protected through the use of zinc anodes. Design/methodology/approach - This study involved electrochemical testing at 24, 35 and 50° C in acidic and neutral solutions. As the environmental temperature and pH change the corrosion potential, galvanic potential and galvanic current may alter. This could influence the expected life of an anode used to protect processing equipment. Accordingly, the experimental design methodology involved collection of corrosion potential, galvanic current and galvanic potential data for zinc and zinc coupled to steel. This information was then used to calculate the life of zinc anodes at different temperatures and pH. Findings - Results indicate that changes in pH and temperature can influence the potential of zinc, the galvanic current in a steel couple and the galvanic potential of zinc joined to steel. Calculations based on the accumulation of these data have revealed that at constant pH as the temperature was decreased, the driving potential of the zinc increased. Through further analysis, it was found that as a consequence of changes in driving potential the integrity of a structure may be put at risk due to fluctuations in pH and temperature. Practical implications - Practically the research can help predict whether the integrity of a structure protected by zinc sacrificial anodes is at risk depending upon changes in pH and temperature. Originality/value - Previous work was related mainly to galvanic corrosion at one particular pH and temperature. In this investigation, a range of pH and temperature values was used for the application of zinc anodes. The paper will be of value to engineers involved in the design of cathodic protection systems for oil field equipment, where changes in the acidity of the environment may occur due to differing levels of CO2 and H2S entering a structure.