Abstract
Galvanic corrosion between dissimilar materials was investigated using laboratory simulations of oil/gas production environments. Galvanic corrosion of materials used in production equipment (4130, 9 Cr, 13 Cr, 2205, 718, 825, NIC 32, NIC 42, SM 2550, Beta-C Ti, C-276, 925) was studied in corrosive environments which included sweet well produced fluids, sour well produced fluids, heavy brine packer fluids and acidizing fluids. Corrosion coupons of various geometries were used to measure corrosion rates and morphologies. Electrochemical measurements were performed to determine potentials and current densities.
The experimental study found that the severity of galvanic attack is a strong function of the type of corrosion products that form on metal surfaces. Galvanic interactions are mitigated in produced fluids where carbonate and/or sulfide scales dominate the corrosion morphology. Carbonate scales tend to block long-range galvanic currents and sulfide scales tend to short-circuit them. As a result, coupling of dissimilar materials in produced fluids may be less of a problem than sometimes suspected.
In more aggressive fluids, such as acidizing or packer fluids where protective scales do not form, the severity of galvanic corrosion is much more pronounced. In these situations, however, many chromium containing materials actively corrode and their chromium content provides short-range galvanic assistance to dissolution, thus reducing long-range effects provided by coupling to dissimilar materials. A galvanic series was constructed based on coupon data and electrochemical measurements for each of the four environments examined.
