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Comprehensive data on corrosion tests for various materials and environments.

Galvanic interaction between nitrided and non-nitrided material is of concern with regard to downhole tool design. Secondarily, the ability of nitrided material to resist corrosion and the relative performance of the type of nitriding treatment (ion nitriding, quench/polish/quench salt bath nitriding) are also of interest. A test program was developed to obtain data on these issues. Nitrided beams were evaluated using a galvanic coupling arrangement that would provide the desired information. The coupons were exposed to a simulated sweet well produced fluid for 30 days and evaluated for galvanic corrosion.

Galvanic corrosion occurs when two dissimilar materials in electrical contact are simultaneously exposed to a corrosive fluid. In general, the more active alloy of the couple corrodes preferentially while the less active (more noble) material is cathodically protected. The rate of galvanic corrosion is a function of several variables including area ratios, corrosivity of the medium, temperature, fluid velocity, nature of the materials, etc.