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Wet Pipe Nitrogen Inerting (WPNI) – FAQs

Where does most oxygen corrosion occur in wet pipe fire sprinkler systems?

Oxygen corrosion typically occurs in four (4) locations:
  • At the metal adjacent to the trapped air at high points in the piping
  • Under deposits of iron oxide wherever they settle within the piping
  • Just downstream of the fire pump
  • At oxygen depleted area in the small space created at the pipe couplings

Does fire sprinkler supply water contain oxygen that can cause corrosion within the fire sprinkler system piping?

Most wet pipe fire sprinkler systems use fresh municipal drinking water as the fire water supply source.  In order to cause corrosion oxygen gas must dissolve into fresh water.  Then it is available to react with any iron that it contacts.  In the gaseous state oxygen does not cause corrosion.  At room temperature and pressure the solubility of oxygen in fresh water is about 8 parts per million (ppm).  This amount of dissolved oxygen can cause corrosion problems.  However, more than 90% of the oxygen that is available to cause corrosion within wet pipe fire sprinkler systems resides in the air that is compressed and trapped when the piping is filled.

What exactly is Wet Pipe Nitrogen Inerting (WPNI)?

WPNI is a process wherein oxygen is completely excluded from wet pipe fire sprinkler system to prevent oxygen corrosion from occurring within the piping network.

What equipment is required to perform WPNI on a wet pipe fire sprinkler system?

There are four (4) components that are necessary to perform the Wet Pipe Nitrogen Inerting (WPNI) on a wet pipe fire sprinkler system:
  • A source of nitrogen gas (98%+) – this can be nitrogen gas cylinders, nitrogen from a nitrogen generator or nitrogen from a plant source
  • An ECS Nitrogen Inerting Vent attached to the fire sprinkler system piping on a remote main location
  • An ECS Nitrogen Injection Port on the wet pipe fire sprinkler riser
  • An ECS Handheld Gas Analyzer to monitor the oxygen content in the discharge gas

What process is used to exclude the oxygen gas from the wet pipe fire sprinkler piping?

A “fill and purge” breathing process is used to sequentially dilute the air inside the empty piping using nitrogen gas.  Three fill and purge cycles are performed on the piping system.  The nitrogen gas is introduced into the injection port on the fire sprinkler riser and exhausted through the nitrogen inerting vent located on the far main.

How long does it take to perform the WPNI process on a typical 1000 gallon wet pipe fire sprinkler system?

Once the equipment is installed on the wet pipe fire sprinkler system the process generally requires 2 – 2.5 hours from start to finish.

How can the quality of the inerted atmosphere within the piping be measured?

The ECS Nitrogen Inerting Vent is equipped with a quick connect sampling port which can be used to measure the concentration of oxygen in the exhaust gas from the piping network.  After the third breathing cycle, all of the exhaust gas will be 98%+ nitrogen.  At that point the atmosphere within the piping can be considered completely nitrogen inerted.

Is it necessary to perform the WPNI process on the wet pipe fire sprinkler system each time the system is drained?

No.  By adding nitrogen gas during the fire sprinkler system draining process, the inerted atmosphere within the fire sprinkler piping can be maintained.  If the draining protocol is followed, it is not necessary to reinert the wet pipe fire sprinkler system.

What is the performance track record for the WPNI process in controlling corrosion in wet pipe fire sprinkler systems?

ECS invented the WPNI process in 2009.  At this point well over 50 facilities have performed the WPNI process on their fire sprinkler systems.  In every wet pipe fire sprinkler system that has undergone the WPNI process the results has been the same:

  • Before WPNI – frequency of corrosion related leaks increasing
  • Perform the WPNI process
  • After WPNI – Instant results – No more leaks!
  • See ECS WPNI Case Histories

Can the WPNI process be performed on wet pipe fire sprinkler systems that have undergone significant corrosion damage?

On systems that have begun to experience increased leak frequency, it is best to perform a video scope corrosion assessment investigation.  Generally on damaged fire sprinkler systems only about 20-25% of the piping requires replacement.  After the pipe replacement work is completed, the WPNI process is performed and the system can be put back into service.

Can the inerted wet pipe fire sprinkler system be monitored for corrosion activity?

After performing the WPNI process we recommend that an ECS In-Line Corrosion Monitor be installed on one of the branch lines within the fire sprinkler piping network.  An ECS engineer can assist in choosing the appropriate location.