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Return on Investment

Wet Pipe Nitrogen Inerting (WPNI) for Managing Leaking Fire Sprinkler Systems

Any Return on Investment evaluation of corrosion control options in fire sprinkler systems must consider three risk elements to fully gauge the value of the investment as part of an overall risk management assessment: repair and replacement risk, sprinkler system impairment risk, and water leak risk. A parking structure presents different risks from a data center or a retail facility.

The property owner should consider the uniqueness of the asset that is being protected and the relative weighting of the various risks mentioned above. For example, shutting down a retail store to repair a leak has tangible hard costs and liability risks. Shutting down a clean room that is part of a manufacturing system would have much higher business continuity risk exposure.


Relative Costs for Fire Sprinkler System Repair/Replacement vs. ECS WPNI Treatment


Black Steel Wet Pipe System (no corrosion protection) – schedule 10 mains and schedule 10 branch lines
  • Average cost of installation – $2-4 per square foot (varies based on geographic location)
  • Average time to first corrosion related leak – 10-15 years (Note that average leak repair cost is $1500-$2500 per leak)
  • Average time to replacement of branch lines and some mains due to corrosion – 15-20 years

Black Steel Wet Pipe Systems (no corrosion protection) – schedule 10 mains and schedule 7 branch lines
  • Average cost of installation – $2-3 per square foot (varies based on geographic location)
  • Average time to first corrosion related leak – 8-10 years (Note that average leak repair cost is $1500-$2500 per leak)
  • Average time to replacement of branch lines and some mains due to corrosion – 12-15 years

Fire Sprinkler Systems protected with Wet Pipe Nitrogen Inerting (WPNI)
  • Additional initial cost for materials and installation labor = $6000 per system – average size is 40,000 square feet = $0.15 per square foot
  • Replacement cost for the system = $2.50 X 40,000 Sq. Ft. = $100,000
  • The implementation of the ECS WPNI process results in the elimination of leak risk and extension of the useful life of the fire sprinkler piping – should last as long as the structure

It should be noted that operating conditions have a significant effect on the projected useful life of the installed fire sprinkler systems including: test frequency, drain and fill frequency, temperatures, installation quality, system modifications, etc. Implementation of WPNI may require some very limited pipe replacement (generally less than 20% of the system) which will add some cost.

Relative Costs for Total System Replacement vs. ECS WPNI

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ECS Wet Pipe Nitrogen Inerting (WPNI) – Case Histories

WPNI Case History No. 1 East Coast Museum of Art (8/2010)

Background – New wet pipe fire sprinkler systems installed at this prestigious art museum in 2006 using galvanized steel fire sprinkler piping. Small leaks occur shortly after the completion of construction on riser nipples located on the branch lines. It was determined that the initial leaks were caused by poor make-up of the threaded nipples. In order to repair and replace the nipple pieces, the wet pipe fire sprinkler systems are drained and re-filled each day during the repair process over the course of several weeks. Pin-hole leaks caused by the repeated introduction of oxygen laden air during the repairs begin occurring on the branch lines with regular frequency. High value art work at risk.

Wet Pipe Nitrogen Inerting (WPNI) – ECS was contacted regarding the corrosion problem because of the research that was being done by ECS regarding the acute vulnerability of galvanized steel piping to oxygen corrosion in fire sprinkler systems. Although it had never been done before, the Wet Pipe Nitrogen Inerting (WPNI) process was deployed by ECS in conjunction with the consulting engineering firm in August of 2010. The ECS Protector Nitrogen Inerting Vent and Nitrogen Injection Port were used for the first time.

Results – The nitrogen inerted atmosphere has been maintained within the system piping since the systems were inerted and there have not been any recorded leaks in the fire sprinkler systems since the WPNI process was performed.

WPNI Case History No. 2 West Coast Mission Critical Aerospace Manufacturing Facility (10/2010)

Background – 1.0MM square foot manufacturing facility with 25 wet pipe systems averaging 1,800 gallons per system in 65 foot high bays. Wet pipe fire sprinkler systems of varying ages from 2-25 years in various stages of repair and replacement. Increasing corrosion related leak frequency throughout the facility – averaging 1 leak every other week. Total annualized cost of repairs at approximately $200,000. Video scoping of the piping in the systems revealed trapped air throughout the wet pipe branch lines and large accumulations of corrosion debris in the mains.

Wet Pipe Nitrogen Inerting (WPNI) – Decision made by facilities management and the fire marshal to use ECS WPNI technology. The mains were flushed using fresh water from the far main to the main drain using a reverse flow of pressurized water to remove the accumulated corrosion debris.

Results – All 25 of the wet pipe systems in the facility were nitrogen inerted using the ECS WPNI technology. There have not been any recorded leaks in any of the fire sprinkler systems since they were inerted in October of 2010. After 18 months one of the fire sprinkler systems needed to be drained to be modified. When the system was drained, the effluent water was crystal clear with no black water or any corrosion debris. This was clear evidence that the oxygen corrosion process had been arrested.

WPNI Case History No. 3 Regional Mall in Florida (12/2012)

Background – Large regional mall with 36 large wet pipe systems constructed in 2001. As with any mall, tenant turnover requires frequent modifications to the fire sprinkler systems. These modifications require that the fire sprinkler systems be drained and refilled frequently during the remodels. Those wet pipe systems that are modified most frequently exhibit the greatest tendency to begin leaking due to oxygen corrosion.

Wet Pipe Nitrogen Inerting (WPNI) – Mall management decides to use the ECS WPNI technology. All 36 systems are nitrogen inerted and the nitrogen atmosphere is maintained using the ECS inerting protocols during any subsequent fire sprinkler system modifications.

Results – There was one leak recorded within 60 days of nitrogen inerting. Since that time there have not been any additional recorded leaks in the 36 sprinkler systems.

WPNI Case History No. 4 Warehouse Facility in Indiana (1/2013)

Background – 450,000 square foot warehouse facility built in 1999 with 12 large wet pipe fire sprinkler systems comprised of 6” mains, 4” floating mains and 2” branch lines following the roof line to a center peak in the middle of the building. Approximate volume of 1,800 gallons per system. Leaks occurring at the high points on the branch lines adjacent to trapped air on one of the systems about every other week.

Surgical Pipe Replacement and WPNI – One 20 foot section of the schedule 7 branch line was replaced on either side of the roof peak. The ECS WPNI process was performed on each of the wet pipe systems.

Results – The projected replacement cost for the fire sprinkler systems was $2 per square foot for a total of $900,000. The surgical pipe replacement and WPNI process was delivered for $90,000 for a 90% cost savings. There have not been any recorded leaks in the 12 systems since the project was completed in January 2013.