Corrosion of Piping in Dry and Preaction Fire Sprinkler Systems: Interim Results of Long Term Corrosion Testing Under Compressed Air and Nitrogen Supervision

摘要

Internal corrosion of dry and pre-action systems is an ongoing and ever growing problem for owners and operators of such systems. The use of nitrogen as a supervisory gas instead of compressed air is one of several techniques that have been put forth as a way to prevent or retard corrosion. In order to fully investigate and compile verifiable data about the efficacy of nitrogen as a supervisory gas, long-term exposure tests were set up in 2009. Sprinkler pipe sections were assembled to simulate in-service, dry sprinkler piping with residual water. The three different conditions currently being tested in black and galvanized steel, schedule 10, 2 1/2-inch diameter pipe are compressed air, 95% nitrogen, and 98% nitrogen as supervisory gas. This paper provides a summary of data accumulated to date and presents some of the interim findings at approximately the halfway point of the projected 7-year testing program. The corrosion mechanisms at work in the different environments are discussed and illustrated with images and analytical data obtained during periodic removal of pipe spools from each of the test systems. The benefits of nitrogen as a supervisory gas are explained and compared to the as-found condition of pipe after extended exposure to such environments in the presence of residual water. Finally, the efficacy of 95% versus 98% nitrogen is compared based on our findings to date. Earlier results of this ongoing study have been previously reported.