Impact of corrosion product removal to depth of corrosion damage in weldment joint

Abstract

Corrosion flaws in pipelines can caused severe financial losses and also can be dangerous for people. One of the most frequently damaged parts are dissimilar pipe welds. We would like to understand how corrosion process reacts on corrosion product removal. Outputs from experiment will be used for production of test specimens. For testing we chose standard dissimilar weldment used in Czech power plants. It is joint with 08Ch18N10T and 22K (GOST) steel. Joint is cut to 24 same specimens. There are exposed to flowing water solution of 5% NaCl. Half of the specimens are regularly mechanically cleaned. The joint is metallographically observed and parts with and without corrosion products are compared. Water salt solution increased pH from 7,25 to 7,86 during 31 days test and conductivity varies around 74 mS cm−1. Metallographic observation indicates that corrosion under corrosion products layer is locally speed up and causes pitting corrosion. Cleaned specimens indicate plane corrosion with lower depth. These results indicate that slag in pipeline could locally speed up corrosion depth penetration. On the other hand, solutions with abrasive particles (which can wipe out the corrosion product) will probably facilitate plane corrosion damage on pipeline walls. This test brings us another knowledge, how to simulate realistic corrosion damage for production of NDT qualification test pieces.