Abstract
The degree of localized seawater corrosion of welds on offshore structures and vessels is a function of the severity of the operating environment, the corrosion susceptibility of steels developed for improved weldability and low temperature toughness, the electrochemical incompatibility between base plate and deposited weld metal, the welding parameters involved and the post weld heat treatment used. An efficient laboratory tool, based on the scanning reference electrode technique (SRET), has been developed to predict the susceptibility to preferential corrosion of weldments in offshore environments. Long-term field testing has been conducted on numerous corrosion coupons and actual hull welds to obtain in situ relative corrosion rates. These results have been successfully correlated with short-term laboratory companion coupon tests. The adaptation of the SRET is demonstrated for predicting the location and severity (i.e. the "anodic hot spots") for preferential corrosion attack. To quantify the parameters which have the major influence on preferential corrosion, a new "chemical equivalent" and "hardness index" are proposed. Analogous to the common carbon equivalent for determining the weldability of steels, a chemical equivalent and hardness index can be calculated for designing welding procedures and developing new steels for minimum localized corrosion susceptibility.
