| Abstract: | An instance where a pre-commissioning hydrochloric acid clean caused localised corrosion of the heat-affected-zones (HAZ) in a carbon steel containing 0.25/0.3%C (ASTM Grade 210C) is described. The factors influencing the occurrence of corrosion at welds during chemical cleaning have been examined. In inhibited hydrochloric acid it has been shown that undesirably high weight losses are associated with pitting and a pitting potential below which pits will not initiate can be determined. Although the susceptibility to attack was different for welds in different steels, all steels were susceptible to localised attack. This susceptibility was reduced but not removed by a stress relieving post weld heat treatment. The use of inhibited citric acid, as an alternative acid cleaning solution, reduces but does not eliminate the possibility of localised weld corrosion. It is recommended that each material/weld combination be tested for susceptibility to localised attack prior to it being cleaned. This should be performed under dynamic conditions using a potentiostat or oxidising additions to examine how near the corrosion potential is to potentials promoting localised corrosion. |
