Abstract
Geothermal systems experience a wide range of environments and temperatures and are susceptible to localized corrosion. Due to the potentially highly corrosive conditions, CRAs are used for the equipment. As part of a broader study, various CRA, including Titanium Grade 2, were tested to help develop and validate the Mixed Solvent Electrolyte corrosion model for predicting localized corrosion susceptibility at higher temperatures representative of geothermal systems.
Grade 2, a commercially pure titanium alloy, forms a protective oxide film which aids in resistance to harsh environments. Unlike stainless steels where crevice corrosion grows with increasingly positive potentials relative to the repassivation potential, Grade 2 becomes more passive. This requires an alternative test method from the standard cyclic potentiodynamic polarization or potentiodynamic-galvanostatic-potentiostatic techniques used to evaluate localized corrosion susceptibility of CRA. Although several studies are reported in literature on localized corrosion testing of Ti alloys, detailed experimental procedures are lacking.
Experimental work was performed to study the localized corrosion susceptibility of Grade 2 in geothermal environments and develop a reproducible electrochemical test method to measure crevice repassivation potentials of Ti alloys. Results were compared with literature for creviced Grade 2 in high chloride environments at high temperatures. This paper discusses the lessons learned and the details of the test method.
