51313-02846-Interim Results of Long Term Corrosion Testing Under Compressed Air and Nitrogen Supervision

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Product Number: 51313-02846-SG

ISBN: 02846 2013 CP

Author: Ockert Van Der Schijff

Publication Date: 2013

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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 this type of 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. Mock-up sprinkler pipe sections were assembled to simulate in-service dry sprinkler piping with residual water. Three different conditions are being tested in containing both black and galvanized steel schedule 10 pipe with respectively compressed air 95% nitrogen and 98% nitrogen as supervisory gas.

This presentation provides a summary of data accumulated to date and present 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 are illustrated with images and analytical data obtained during periodic removal of pipe spools from each of the test systems. The theoretical benefits of nitrogen as a supervisory gas are explained and compared to the as-found condition of pipe exposed to such environments in the presence of residual water. The perceived threat of microbiologically corrosion (MIC) under such conditions is discussed and data of microbiological testing conducted on some of the test spools are presented. Finally the efficacy of 95% versus 98% nitrogen is compared based on findings to date.