Air Trapped at Top of Main

Illinois Distribution

WPNI: Wet Pipe Nitrogen Inerting

Project Background:
Specifics on subject building:
  • Large distribuon center located in Illinois – open floor construcon
  • 376,000 sq. . of fire sprinkler system coverage area
  • 13 individual wet pipe risers serving the building, average zone volume 1,200 gallons
  • 6” mains with 2” branch lines following the roof pitch to the center of the building; 4” floang main on the opposite wall
  • Building age: 24 years
Corrosion related leak history:
  • Leaks occurring in branch lines at apex of building on the branch lines
  • Leaks occurring on the top side of the mains at the mechanical tee connecon for the branch lines
  • Content damage risk due to fire sprinkler water leak
  • $25,000 cumulave repair expenses
Fire sprinkler piping materials:
  • Mechanical tees at riser nipples off of the mains
  • Threaded schedule 7 XL piping, galvanized coang on the exterior pipe surfaces

Preliminary Assessment Work

To determine the root cause for the corrosion related leaks within the fire sprinkler system a corrosion assessment study was performed. The assessment included:

  • Study of repair and pipe replacement history
  • Elemental analysis of the supply water and deposits from the systems
  • Profile of microbial contaminaƟon throughout the systems
  • Failed pipe analysis – extent of damage, pit depth, metal loss characterisƟcs
  • Video scoping of the fire sprinkler piping system

Corrosion on BoƩom of Branch Line


Corrosion on BoƩom of Main

  • Perform limited pipe replacement of the 2” branch lines on either side of the roof apex, approximately 60 feet of pipe on each branch line
  • Install ECS Protector Nitrogen Inerting Vents on each of the wet pipe zones
  • Install ECS Protector Nitrogen Injection Ports on each of the wet pipe risers
  • Perform nitrogen inerting of the fire sprinkler systems using the ECS nitrogen inerting protocol for wet pipe fire sprinkler systems
  • Use nitrogen cylinders to supply the necessary nitrogen gas for the inerting procedure on the fire sprinkler systems
nitrogen-vent ECS Nitrogen Inerting Vent

Financial Analysis of Repair Options

The most common response to escalating leak frequency and increasing fire sprinkler system repair costs is to completely remove and replace the fire sprinkler system piping. Esmated replacement cost of the fire sprinkler piping for this facility was $2 per square foot for a total of approximately $900,000.

Preliminary Assessment Work

The owner and fire sprinkler contractor decided to apply Engineered Corrosion SoluƟons wet pipe nitrogen inerƟng technology based on the results achieved from other WPNI applicaƟons in similar condiƟons.

The video scoping evidence proved conclusively that 80% of the 24‐year‐old piping in place had very liƩle internal corrosion damage. The piping components that exhibited corrosion were selecƟvely replaced. During the month of July 2011 nitrogen inerƟng vents and injecƟon ports were installed on each of the zones. The total cost to the owner for deploying the limited pipe replacement/nitrogen inerƟng approach was $80,000. RepresenƟng an approximately 90% total reducƟon in repair costs. Since iniƟal inerƟng of the 13 wet pipe fire sprinkler systems there have been no leaks reported at the facility.

pressurized-cylinders-provide Pressurized Cylinders Provide Nitrogen Gas through injection ports at risers

Fire Sprinkler Contractor Feedback

Fire sprinkler contractors who have performed the wet pipe nitrogen inerting (WPNI) procedures report that the entire process is very manageable and significantly easier than applying chemical corrosion control agents. The entire wet pipe nitrogen inerting procedure can easily be performed on a typical 1,000 gallon sprinkler system within 2‐3 hours. It is also possible to perform the procedure on several zones at the same me. Once the fire sprinkler contractor has been certified by the ECS Nitrogen Inerting Team, the contractor does not require on‐site support or supervision.

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