Corrosion in water based sprinkler systems (wet or dry) continues to be a major problem for building owners. As the system ages corrosion of metal occurs due to exposure to oxygen. As the old adage goes “what you can’t see can hurt you” definitely applies to corrosion of water based systems because it is not visible.
Once corrosion reaches a critical level it can cause costly failures. These failures can lead to loss of life and/or property, water damage, and under performance of systems when they are needed during an emergency. Not having required inspections completed is a huge risk because these inspections inform building owners and delegated personnel in charge of maintenance of corrosion problems.
Two Things to Consider on How to Mitigate Corrosion
Although rates of corrosion vary per system, it is critically important for building owners to consider the design of the system. At no time should one consider deviating from code standards because any change for short term savings could substantially cost building owners in the future. NFPA 13 is the Standard for the Installation for Sprinkler Systems and should be used as a resource during design and installation of sprinkler systems.
One important decision is what piping to use. Whether cast iron, black steel or galvanized piping should be used varies depending on application and code. Cast iron is very susceptible to corrosion and many types of supply mains have found to be obstructed by 50% due to corrosion.
For dry systems (pressurized with air and not containing water in the system thus “dry” until activated) the decision whether to use black steel and galvanized pipe depends on cost and the C factor. The C factor indicates the smoothness of the interior of a pipe (120 for galvanized and 100 for black pipe) and can offset the additional upfront cost of galvanized pipe over the life of the system. However, if the pipe isn’t pitched correctly or specific gaskets aren’t used water/oxygen interfaces can occur, causing the interior of galvanized piping to corrode more rapidly than if black steel pipe were used.
2. Inspections, Testing & Maintenance
NFPA 25 is the Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems. It provides the maintenance frequencies for wet and dry systems as well as the components such as pipe, fittings, gauges, valves, etc. This includes inspection and testing for standpipe and hose systems, fire pumps (where applicable) and fire department connections. The first edition of NFPA 25 was published in 1992 and the latest version is edition 2020. A great deal of care and thought is put in updating each edition by industry professionals. It recommends that building owners shall test water flow devices quarterly.
Additionally, hydrostatic testing for dry systems and standpipe flow tests should be conducted every 5 years to make certain water is flowing freely throughout the system and corrosion deposits have not clogged the piping and integrity is maintained. Additionally, every 3 years the dry system must undergo a full trip test to document the water delivery time to ensure the system can deliver water to the remote sprinkler.
Untreated raw water sources such as ponds, rivers, and lakes are used as fire protection water supplies where public water is not available or not available in quantity. If the water is not properly treated, organic growth, bacteria, debris, and mineral deposits can be introduced into the system, and piping. If this is the case, extra attention and care should be paid to the system because the likelihood of obstructions and clogs increase tremendously.