Report: Identification of root cause failure of piping in a service water system

This report deals with studies on the identification of the root cause of piping failures in a service water system, and to develop a proposal for action to prevent further failures. The failures were characterized as pin hole through-wall penetrations associated with butt-welds, restricted to stagnant flow carbon steel piping. Based on extensive tests, inspections and observations the conclusions presented in this report are summarized as follows: (1) the pin hole failures were characterized as root cause, microbiologically influenced corrosion (MIC), this conclusion was based upon microbiological, visual, and chemical testing at the as-is site of a recent failure, pipe segments were available for extensive testing and comparison to previous failures; (2) failures were isolated to stagnant sites at points where poor weld penetration provided optimum conditions for MIC to occur; (3) extensive examination of the process flow and intermittent flow sites characterized as high risk areas were made, no evidence of microbiological involvement with corrosion was found, no evidence of any type of significant pitting corrosion was found at these sites; (4) removal and replacement of stagnant line and weld sites was done as a major step in preventing further failures. MIC inoculum, primarily anaerobic microorganisms, was found at many anaerobic and aerobic sites in the system. This suggested that a preventive chemical treatment program would be appropriate to maintain the system at a MIC free status. A monitoring program was suggested to assess on a real-time-basis, the potential for MIC and to monitor the mitigation of MIC