System and method for fire protection system corrosion mitigation

Abstract

An inert gas Fire Protection System (FPS) uses an inert gas rather than air in a dry or pre-action type FPS. The inert gas inhibits oxidation, galvanic corrosion, and/or bacterial growth, and hence mitigates Microbiologically Influenced Corrosion (MIC) and galvanic corrosion in the FPS piping. A zone purging valve, which may include a gas purity analyzer, is disposed at the end of each zone in the FPS. A controller over-pressurizes the FPS with inert gas, and bleeds the gas through the zone purging valves to a predetermined supervisory pressure. The pressurize/purge cycle is repeated to ensure inert gas of a predetermined purity level reaches all areas within the FPS. The purity of the inert gas is periodically measured in bleed operations. The inert gas may comprise Nitrogen, which additionally dries out residual water in the FPS due to a low dew point, further inhibiting MIC.

1 . A method of inhibiting corrosion in fire protection system piping, comprising:
 hydro-testing the fire protection system;   draining water from the fire protection system piping;   purging oxygen in the fire protection system piping by replacing it with an inert gas; and   maintaining the inert gas in the fire protection system piping at a predetermined supervisory pressure and at a predetermined purity level.   
     
     
         2 . The method of  claim 1  further comprising removing residual water remaining in the FPS after draining. 
     
     
         3 . The method of  claim 2  wherein removing residual water comprises
 introducing a low dew point gas into the fire protection system piping;   allowing the residual water to evaporate into the gas; and   purging the gas from the fire protection system piping.   
     
     
         4 . The method of  claim 1  wherein the inert gas is nitrogen. 
     
     
         5 . The method of  claim 1  wherein purging oxygen in the fire protection system piping by replacing it with an inert gas comprises (a) purging the oxygen in the fire protection system piping with inert gas;
 (b) pressurizing the fire protection system piping with inert gas at a pressure in excess of the predetermined supervisory pressure;   (c) bleeding the inert gas from the fire protection system piping into one or more gas analyzers;   (d) repeating steps (b) and (d) until the inert gas reaches the predetermined purity level.   
     
     
         6 . The method of  claim 1  wherein maintaining the inert gas in the fire protection system piping at a predetermined supervisory pressure and at a predetermined purity level comprises monitoring the inert gas pressure and introducing inert gas into the fire protection system piping if the pressure falls below the predetermined supervisory pressure. 
     
     
         7 . The method of  claim 6  wherein monitoring the inert gas pressure further comprises triggering one or more alarms if the inert gas pressure is detected below the predetermined supervisory pressure. 
     
     
         8 . The method of  claim 7  wherein a first alarm is triggered if less than a first volume of inert gas is required to maintain the inert gas pressure at the predetermined supervisory pressure within a predetermined duration. 
     
     
         9 . The method of  claim 8  wherein a second alarm is triggered if more than the first volume but less than a second volume of inert gas is required to maintain the inert gas pressure at the predetermined supervisory pressure within the predetermined duration. 
     
     
         10 . The method of  claim 9  wherein a third alarm is triggered if more than the second volume of inert gas is required to maintain the inert gas pressure at the predetermined supervisory pressure within the predetermined duration. 
     
     
         11 . The method of  claim 1  wherein maintaining the inert gas in the fire protection system piping at a predetermined supervisory pressure and at a predetermined purity level comprises periodically bleeding inert gas through one or more gas analyzers to monitor the purity of the inert gas. 
     
     
         12 . A fire protection system, comprising:
 piping operative to carry water over areas to be protected from fire;   one or more sprinkler valves operative to discharge water when a fire is detected;   an inert gas control system in gas flow relationship with the piping and operative to selectively inject inert gas from an inert gas source into the piping, and further operative to monitor and control the pressure of the inert gas in the piping; and   one or more analyzing vents in gas flow relationship with the piping, disposed remotely from the inert gas control system, and operative to controllably vent gas from the piping and further operative to analyze the purity of the vented gas.   
     
     
         13 . The system of  claim 12  wherein the analyzing vents are additionally connected in control relationship to the inert gas control system, and wherein the inert gas control system is further operative to control the analyzing vents' operation. 
     
     
         14 . The system of  claim 12  wherein the analyzing vents are further operative to report the measured purity of vented gas to the inert gas control system. 
     
     
         15 . The system of  claim 14  wherein the inert gas control system is operative to control both the pressure and purity of inert gas in the piping by
 periodically controlling one or more analyzing vents to vent inert gas and measure its purity;   receiving a report of the vented gas purity from the analyzing vents; and   selectively inject inert gas from the source into the piping, in response to the pressure and purity of inert gas in the piping.   
     
     
         16 . The system of  claim 12  wherein the inert gas is nitrogen. 
     
     
         17 . The system of  claim 16  wherein the inert gas source comprises one or more pressurized nitrogen tanks. 
     
     
         18 . The system of  claim 16  wherein the inert gas source comprises a nitrogen generator operative to generate nitrogen from air. 
     
     
         19 . The system of  claim 12  wherein the inert gas control system is further operative to trigger one or more alarms in response to the inert gas pressure in the piping. 
     
     
         20 . A method of assessing the leak rate in a Fire Protection System (FPS) comprising a plurality of pipes operative to carry water, comprising:
 affixing a pressure transducer in pressure sensing relation to the FPS;   linking the pressure transducer in data flow relation to a data logger;   pressurizing air in the FPS piping to a predetermined supervisory pressure;   recording the drop in air pressure in the FPS piping, from the predetermined supervisory pressure, as a function of time; and   calculating the air pressure leak rate of the FPS.   
     
     
         21 . The method of  claim 20  wherein affixing a pressure transducer in pressure sensing relation to the FPS comprises affixing the pressure transducer to an existing test port that includes a ball valve. 
     
     
         22 . The method of  claim 20  wherein affixing a pressure transducer in pressure sensing relation to the FPS comprises affixing the pressure transducer to an existing supervisory pressure air compressor accumulator tank. 
     
     
         23 . The method of  claim 20  wherein linking the pressure transducer in data flow relation to a data logger comprises connecting the pressure transducer to the data logger via a wired connection. 
     
     
         24 . The method of  claim 20  wherein linking the pressure transducer in data flow relation to a data logger comprises connecting the pressure transducer to the data logger via a wireless connection. 
     
     
         25 . The method of  claim 20  wherein the pressurizing step is repeated as the FPS pressure drops to a predetermined trigger pressure. 
     
     
         26 . The method of  claim 25  wherein the recording step continues over a predetermined duration, during which the pressurizing step may be repeated a plurality of times. 
     
     
         27 . A gas purging valve operative to be connected to piping in a Fire Protection System (FPS) and to bleed gas at a predetermined rate, comprising:
 an inlet in gas flow relationship with the FPS piping;   a central passage in gas flow relationship with the inlet;   a calibrated orifice removeably disposed in the central passage, in gas flow relationship with the passage and operative to allow a maximum predetermined gas flow rate therethrough;   an outlet in gas flow relationship with the calibrated orifice; and   a ball disposed upstream of the central passage, the ball operative to allow gas flow through the gas purging valve but operative to impede the flow of water through the gas purging valve.   
     
     
         28 . The valve of  claim 27  further comprising an o-ring disposed upstream of the central passage, the o-ring sized and positioned such that water pressure at the inlet urges the ball against the o-ring, sealing the central passage against water flow therethrough. 
     
     
         29 . The valve of  claim 28  wherein the ball and the o-ring are disposed in the inlet. 
     
     
         30 . The valve of  claim 27  wherein the outlet is adapted to be connected to a gas purity analyzer.