As the fire sprinkler industry seeks answers for mitigating corrosion risks, it is important that sound scientific solutions be developed and deployed. There have been several myths regarding corrosion that have hindered the implementation of effective corrosion control strategies. In order for the industry to move forward these myths must be dispelled so that effective solutions can become standard practice.
Myth No. 1: MIC, MIC, MIC – Microbiologically Influenced Corrosion is the primary cause of pin-hole leaks in fire sprinkler systems.
Oxygen gas is the primary cause of corrosion and pin-hole leaks in fire sprinkler systems. Oxygen removes metal from the pipe walls and creates insoluble solid by-products which can create obstructions within the piping. Bacteria are always present in fire sprinkler systems. If you look for them you will find them. There is very little correlation between the level of microbial contamination and corrosion related leaks. Results from hundreds of analytical samples indicates that bacteria cause fewer than 10% of the pin-hole leaks that occur in fire sprinkler systems. Oxygen corrosion produces the balance of the leaks.
Myth No. 2: Galvanized Steel Piping Performs Better Than Black Steel in Preventing Corrosion in Dry Pipe Systems
Galvanized steel piping for dry pipe fire sprinkler systems can begin leaking 3-4 times faster than black steel piping that is exposed to identical operating conditions. Under a pool of trapped water within a galvanized dry pipe system oxygen corrosion is highly localized and leads to the creation of deep pits in the metal. In black steel pipes oxygen corrosion is much more dispersed and causes general thinning of the pipe wall under the pools of trapped water. Galvanized steel piping also averages a 30% cost premium compared to black steel piping. Galvanized pipe costs more and fails faster than black steel.
Myth No. 3: Once a Fire Sprinkler System Starts to Have Frequent Pin-Hole Leaks, It Must be Replaced to Stop the Leaks
When fire sprinkler systems are removed and replaced because they leak too much, inspection of the old system piping frequently reveals that less than 20% of the piping has incurred significant damage from corrosion. The majority of the pipe from the demolition and removal has no corrosion at all. Oxygen corrosion in fire sprinkler systems is highly localized. Inspection of the removed piping reveals that oxygen corrosion generally occurs at trapped air pockets in wet pipe systems and at pools of trapped water in dry and preaction systems. It is far more cost effective to remove the damaged piping and then institute a comprehensive corrosion management system.
Myth No. 4: Bad Water Causes Fire Sprinkler System Leaks
Almost all fire supply water comes from municipal water purveyors. For the most part fire supply water is very fresh and very clean. Water chemistry does vary throughout the country but in general it is the introduction of oxygen into the fire sprinkler piping that causes increased leaking not the quality of the supply water.
Myth No. 5: The Quality of Fire Sprinkler Piping and Fittings Has Declined
Failed fire sprinkler piping that shows evidence of material defect from the manufacturer is very rare. The quality of fittings and tubular goods being used today in fire sprinkler systems generally meets or exceeds the ASTM standards. Corrosion at weld seams that is often recognized as the cause of leaks is not the result of materially defective piping. It is the lack of heat annealing of the piping and the subsequent exposure to oxygenated water that causes accelerated attack at the weld seams. Leaks that occur at weld seams in fire sprinkler piping can be completely controlled by keeping the oxygen out of the fire sprinkler system.
Periodic introduction of oxygen to water based fire sprinkler systems always leads to oxygen corrosion. The cumulative amount of oxygen that is introduced to the piping has a direct impact on how fast leaks are created and the service life of the system. When wet pipe systems are drained and refilled frequently they will develop more leaks. When pressure maintenance compressors run more frequently on dry and preaction systems they will develop more leaks. Removing the oxygen and preventing its introduction by inerting the systems with nitrogen can completely stop corrosion. Dry Pipe Nitrogen Inerting (DPNI) and Wet Pipe Nitrogen Inerting (WPNI) are the most effective solution for corrosion control, risk reduction and fire sprinkler system service life extension.