Dissolved oxygen exists naturally within water and creates corrosion-friendly air pockets within pipes of a fire suppression system. A corrosion-proof system needs safeguards in place to minimize the presence of unwanted oxygen that leads to metal breakdown. In this video, we explain different venting methods to eradicate air pockets and common practices to remove unnecessary oxygen from your system.

Video Transcript

Lee: "Let's talk about wet systems. We never spent much time talking about corrosion and wet systems until now. So there's a big box retailer out there that we probably all spend some time shopping at, and that big box retailer was seeing in their stores that they were having leaks in their systems. They then pushed this through the process. They'd heard about nitrogen generators and then that got them to thinking, 'what's happening in our systems?' Well in a wet system, just as in a dry system, we're looking at the air water interface.

If I have trapped water and I have air in my pipes, that air water interface is where I have my corrosion problem. In a dry pipe or pre-action system that happens at the low points, because we drained down the water out of the system. In a wet pipe system that happens high in the system, because I have trapped air pockets at the top of the system. So now we're focusing at the top for having leakage problems. Those trapped air pockets are present in any system and the oxygen that is in the air pocket supports corrosion.

The big box retailer that brought this to the forefront was realizing that they were having pinhole leaks in branch sprinkler lines at the top of their stores where it's as hard to get to as possible. Now another piece of this is the dissolved oxygen in every bit of water out there.

Anytime we're bringing new water into a piping system, there's naturally oxygen dissolved in it. It sits in the pipes, and over time that oxygen comes out and adds to the air pockets within the system. The new code requirement in the 2016 Edition of NFPA 13, the Standard for the Installation of Sprinkler Systems, required under 7.1 for wet systems and air vents says that a single air vent with a connection conforming to 8.16.6 shall be provided on each wet pipe system utilizing metallic pipe.

Well, we use metallic pipe in most systems so we need to have at least one air vent in every system. The code goes on to say, venting for multiple points on each system shall not be required. So they're only requiring you to do one, think about that. How many air pockets do you think you're going to have? Probably more than one.

Manual or Automatic Vents

The air venting required by 7.1.5 shall be located near a high point in the system to allow air to be removed from that portion of the system by one of the following methods; a manual valve a minimum of half an inch in size; or an automatic air vent; or other approved means. The automatic air vent is something we want to talk about. There are a couple of manufacturers that are now marketing air vents to the sprinkler industry.

If you're familiar with other hydronic systems, or other piping systems like heating water systems or chilled water systems, then you know about air vents. Those systems have the same problems with corrosion and we've been installing automatic air vents on those piping systems for a lot of years. Now, that's coming into the sprinkler industry. We suggest you try to discover any trapped pockets of air by focusing on the high points in your system.

There's probably going to be more than one pocket. You can either install a manual vent or an automatic vent. If you want to build on top of that and have a system more resistant to corrosion you can pre-purge the pipes with nitrogen before you fill 'em with water.

Prevention Steps

One option is to use compressed nitrogen cylinders or liquid nitrogen when the system is dry with no water in it. Use this to purge it all with nitrogen and then open up the water valve and fill it with water so that those trapped air pockets now aren’t just regular air, it's nitrogen up at the top. The big box retailer I keep referring to uses this method in addition to the air vents that they install on the system.

Another option is to try and remove the oxygen in the fill water. This is an engineering term I like to use: "belts and suspenders." With belts and suspenders, you have vents, you pre-purge the pipes with nitrogen before filling and then use a system called a deoxygenating system to strip dissolved oxygen out of the water before you fill the system.

There's some debate in the industry whether or not this is necessary to do, but if you feel like it's critical for your facility to never have a leak, this might be an option for you."

Audience: "If you have hard water or anything like that, do you factor that into this?"

Lee: "That really doesn't have an effect. Soft water, hard water, it doesn't matter.

We don't want you to be these guys though as far as leaks go. What, what are those wrapped around the pipes?"

Audience: "Looks like diapers."

Lee: "Diapers. This is another story out of Florida, by the way, a lot of the crazy things happen in Florida. This is a facility that's an indoor storage locker and it's sort of a low budget operation. They were having leaks with their dry pipe sprinkler system and instead of fixing those leaks or installing a nitrogen generator, they just decided it was cheaper to go buy a box of diapers every week and have somebody go wrap those diapers around the leakage points in the system."

Audience: "Are those UL listed or CPVC?"

Lee: "UL Listed, well no but they're FM approved."

This concludes our 4-part video series on fire protection system corrosion and leaks. This video series is part of an extensive video program with educational topics on everything fire protection. View the index below to watch other videos or register for one of our upcoming events for a hands-on learning experience.