Nationwide Distribution Centers

WPNI: Wet Pipe Nitrogen Inerting

Project Background

A distribution company with a nationwide footprint contacted ECS in 2016 to find a way to quantify the risk the aging fire sprinkler systems posed throughout the portfolio of their properties. 

The prior year, two of their locations experienced a significant number of leaks on the wet pipe systems, resulting in a large expenditure on emergency repair calls, property damage, disruption of business, and ultimately replacement of the system piping.

To be able to better forecast future capitol expense required to repair or replace sprinkler piping, they contracted ECS to perform corrosion assessments on twelve (12) of their locations. These investigations were preformed in the span of several weeks and looked at representative samples of 92 wet systems protecting the various facilities.

This provided a unique view of the factors that lead to accelerated corrosion in wet system piping and gives building owners the ability to focus limited resources on addressing those systems that are most likely to develop leaks first.

Assessment of the Corrosion Damage

The buildings selected for the corrosion investigations ranged from 5-44 years in age. Surprisingly, the age of the system piping did not directly correlate to the severity of the corrosion found. Rather, the two primary factors influencing the amount of metal loss found was the system design/layout and the amount of activity the system had seen since the initial install. The design/layout of the systems can be grouped into three categories:

  • Flat system, with little to no pitch on the branch line or main piping
  • Pitched system, with the branch lines running upslope and terminating at the roof/system peak
  • Pitched system, with the branch lines running flat, parallel to the slop of the roof

Flat System, Little to no Pitch to System Piping

Those systems that had experienced the least amount of corrosion, including the oldest 44-year-old systems, were installed relatively flat. This configuration results in trapped air being spread throughout the system, rather than localized to any one point. While corrosion still occurs, the metal loss is spread out throughout the system, limiting the severity of resulting oxygen corrosion.

14 Year Old Flat System

Figure 1: 14-Year-Old Flat System - Pocket of
Trapped Air in Branch Line with Limited Corrosion

15 Year Old Pitched System
Figure 2: 15-Year-Old Pitched System – Large
Pocket of Trapped Air at System High Point

Pitched System, Branch Lines Running Up Slope

The most significant metal loss was found in those systems whose branch lines followed the slope of the building's roof and terminated at a system high point. This configuration allows all the trapped air in the system to migrate and accumulate at the end of the branch lines, resulting in highly localized corrosion. While this leaves the rest of the system primarily water-filled and in good condition, a leak will develop very quickly at the air/water interface near the system high point where water meets air.


Pitched System, Branch Lines Run Flat Parallel to the Slope of the Roof

A third subset of systems are those that follow the pitch of the roof, but the branch lines run flat parallel to this pitch. When the lines are fed by riser nipples off the top of the main, every branch line will act to trap air. However, those branch lines closer to the peak of the system will contain a larger pocket of trapped air.

The last factor that heavily influences to the severity of corrosion in wet system piping is the frequency with which it is drained and filled. The primary ingress of fresh air into the system piping occurs during drain downs. Those systems that had been relatively untouched since initial install appeared to be in excellent condition, while those that had undergone large scale tenant modification projects that required frequent draining and filling had experienced significant metal loss.

28 Year Old Low Branch Line-1
Figure 3: 28-Year-Old System - Low Branch
Line, Small Pocket of Trapped Air
28 Year Old High Branch Line
Figure 4: 28-Year-Old System - High Point
Branch Line, Large Pocket of Trapped Air
17 Year Old Sample-corrosion Internal corrosion after sandblasting, pipe sample from 2016 assessment (17-year-old sample)

Final Takeaways

Based on the findings of the corrosion investigations, partial pipe replacement was performed in two (2) of the facilities to remove the most damaged piping at the system high point. Eight (8) of the facilities that had experienced moderate corrosion opted to nitrogen inert their wet pipe systems to completely remove oxygen from the piping network and halt ongoing corrosion. The installation of automatic air vents was planned on the remaining facilities to limit future corrosion. No leaks have been reported since the corrosion control strategies were implemented.

Regardless of system layout and activity, the primary method for preventing corrosion in wet pipe systems is to remove oxygen from the piping before it can cause corrosion.

The installation of automatic air vents can exhaust large amounts of trapped air, or ECS’s Wet Pipe Nitrogen Inerting (WPNI) protocol can be used to completely remove all oxygen from the piping network, virtually eliminating future corrosion.

Get Your Project Started with ECS Today

Learn More