Effect of oxygen on pitting corrosion of copper pipe in fire sprinkler system

In this study, pitting corrosion in copper pipe used for sprinkler according to dissolved oxygen (DO) concentration was investigated through failure analyses, flow visualization test, DO consumption rate analysis, electrochemical tests, surface analyses, and corrosion simulation test. As a result of the failure analysis, all 10 leaks were due to pitting corrosion, and 8 leaks occurred in the branch pipe at the end of sprinkler system. As a result of flow visualization test, there were air pockets occupying 20% of the maximum total volume at the end of the branch pipe due to pressure drops. DO consumption rate analysis showed that air pocket acted as the oxygen source to maintain high DO concentration. As a result of electrochemical tests, surface analyses, and corrosion simulation, the corrosion rate of the higher DO concentration is about 10 times higher than that of lower DO concentration due to the increased oxygen reduction reaction. Through these results, it was confirmed that an air pocket was formed at the end of the pipe in the sprinkler system, and this air pocket became an oxygen source and accelerated galvanic corrosion between inside and outside of the pit during pitting propagation. This can be used as a guideline to prevent water leakage for pitting corrosion on copper pipe.