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Engineered Corrosion Solutions: Wet Pipe Venting and WPNI

Posted by ORR Protection on Mar 12, 2021 9:30:00 AM

Bill Aaron, Director of Training at Engineered Corrosion Solutions, discusses corrosion management of fire sprinkler systems, including air venting and wet pipe nitrogen inerting for wet pipe sprinkler systems.

Wet Pipe Venting and WPNI


Video Transcript:

Hello. My name is Bill Aaron. I'm the Director of Training for Engineered Corrosion Solutions. And I want to thank you for taking time out of your schedule to be with us today. What we'd like to discuss is corrosion management for fire sprinkler systems, which includes air venting and wet pipe nitrogen inerting for wet pipe sprinkler systems. So let's get started. First. The thing to remember is that oxygen is a primary cause of corrosion and fire sprinkler systems. Anytime that you have oxygen, liquid, water and steel together, you're going to get iron oxide or rust.

Now that that rust or that iron oxide that you see is a lot, like if you took a piece of steel, you threw it out on the ground and it rained on it and it would start rusting. This is the same thing is happening inside the sprinkler systems. How fast is this process? Start we'll look at your rotors right after a rain storm or after you go to the carwash and you see that orange discoloration on your rotors, that's the oxidation process is happening. It happens that quick now in wet pipe, sprinkler systems, the corrosion is a result of the sprinkler system being open to atmosphere. And as it's filled up with water, the atmosphere is pushed to the high points in that sprinkler system and that trapped air, along with the location of where the water is, that's called an air water interface. It attacks the steel and that same location pulls a pit of steel out of the, out of the steel.

And it falls to the bottom of a pipe, which becomes the iron oxide or the sludge that's seen the bottom of the pipe when it first through the first part of the process is more orange-ish in color, and that's called hematite as the process continues. It turns black and that is called magnetite. Now, a few things to remember about fire sprinkler systems, fire sprinkler systems are a very complex stagnant vessel. And the most important thing is the fact it's stagnant. There is not water flowing in them. Once you fill them up, they sit there and they wait, nothing happens. So that oxygen that has to dissolve in the water, attacked us steel and become a pit laying in the bottom of it. The thing is oxygen in water has very limited mobility. That means the oxygen that's attacking. The steel is very close to the air water interface.

The other thing is oxygen molecules have very limited solubility. There's only a specific amount and it's 10 parts per million that can dissolve into the water before it becomes saturated and no more oxygen can Kenya dissolve there. Something has to happen that reaction of the oxygen, attacking the steel, pulling the pit out, allows more oxygen to be saturated into the water to continue the process. Now, the thing too is that once that oxygen is gone, the corrosion process stops. So as an example, if you were to measure the air pocket in a wet pipe sprinkler system, right after you filled it, you would see 21% oxygen because the air we breathe is 78% nitrogen and 21% oxygen. If you came back 90 to 120 days later and you measured it again, it would be a zero oxygen because it takes about 90 to 120 days for that oxygen to dissolve in water attack, to steal and become the sludge in the bottom of the pie.

Now, some factors that affect the corrosion process, more oxygen means more corrosion. The more activity, the more times you drain it and refill it, the more times you repair it, the more times you do remodel work or reload, work on it. Every time that you drain that sprinkler system down and you open it up to atmosphere and you fill it back up and you're putting fresh oxygen molecules back into that sprinkler system and it's causing corrosion activity in the system. The other thing we've found is dry pipe systems fail faster than wet pipe systems. Reason being is on a dry pipe system. You have an air compressor that keeps a supervisory gas on that sprinkler system to make sure it stays intact. But the thing is every time that air compressor turns on, it's putting fresh, warm, more oxygen back into that sprinkler system. You've got a continuous flow of oxygen in a dry pipe system.

More oxygen means more corrosion there. It fails faster. The other thing we found is that galvanized pipe fails fast from the black steel. We thought galvanized pipe would be a good thing for fire sprinkler systems, but in reality, it's not, it's actually worse. The reason is when you look at galvanized pipe, it galvanized pipe is nothing more than black steel pipe that has a zinc coating over the top of it. That is encoding has to dry. Once it dries, it becomes a zinc carbonate. That's that white milky color you see on signposts and guardrails right after a rainstorm that's is in carbonate. That protects it. The problem inside of spray a sprinkler system is that it's never dry. It's always wet. And when it's wet like that, that zinc coating lifts off. Well, now that's encoding lifts off and the oxygen molecules attack that bare steel, see corrosion is looking for anomalies, looking for something different.

And the difference between the galvanized pipe and the black steel is that difference in as white attacks. The other thing, temperature affects corrosion activity. It's just a chemical reaction for every 18 degrees Fahrenheit. You're in your corrosion activity is double. So it's 70 degrees. You've got a specific level of corrosion activity at 88. It's doubled at one Oh six it's quadrupled. So if you get into buildings where they have hot processes, such as Sam's clubs, where they have ovens in the bakery, those hot processes, cause more. That's where we see more leaks because of the heat. The thing to remember is corrosion is cumulative. Now in what pipes, sprinkler systems, the oxygen that causes a corrosion is in the trapped air. So 99% of the oxygen is in that trap. There there's less than 1%. That's actually in the incoming water source. So if you look at it, you've got 210,000 parts per million in the 21% of oxygen trapped there.

And you've got 1% of oxygen in the incoming water supply, 210,000 parts per million, as compared to 10 parts per million, we're going to focus on the 210,000 parts per million because in the 1% that's an incoming water source. There's there's really no practical way to remove the O from the H2O. The amount of energy is pressed compounded. So in a wet pipe sprinkler system, what do we do? We look for the air water interface, that location, where you have the combination of oxygen, water, and steel. That's the location where you're going to have the corrosion activity. If you look at a wet pipe sprinkler system where it's completely air pack, no water, you won't see any corrosion. If you go to the wet pipe sprinkler system where it's fluid pack, where it's all water, no air, there's no corrosion. It's only those locations where you have the combination of oxygen, water, and steel.

That's where the corrosion activity is now. And it's not just ECS a saying this FM global data sheet 2.1 data sheet says steel piping will rust and corrode in the presence of water and oxygen. It also says remove trapped air from wet pipe, sprinkler systems you can use as a half inch automatic release Val or an approved manual valve. The other thing too, isn't in the days of using chemical inhibitors, FM global has come out and said that those cleaners inhibitors can result in accelerated corrosion or restricted off orifices. So the issue of corrosion and fire sprinkler systems really truly is in the trapped oxygen that's causing the corrosion and nothing else now. And NFPA 13, the 2019 edition also talks about bacterial inhibitors that were put into eliminate out of micro, biologically influenced corrosion and a fire sprinkler systems. What NFPA 13 is telling us is that any inhibitors or anything that you put in that sprinkler system has to be compatible with all the components of that sprinkler system.

The 2016 edition of NFPA 13 has also indicated that you need to put a single air vent on each wet pipe system. And it needs to be at a high point. Now that can be as little as a half inch manual ball valve or an automatic valve. It really doesn't matter. But the thing to remember, if you're you putting, installing this equipment in, you've got to use it every time you fill it. So if you've got a manual valve, you've got to go to that valve and open up the trapped air to get rid of the trap there. Because if you don't get rid of the trap there, you're going to have oxygen corrosion. And the whole process is to eliminate as much of that trapped air as we possibly can. Now there's a couple of, of websites here that can go to NFPA in the code finder.nfpa.org.

And you can see what jurisdictions have adopted the 2016 edition of the inner of the NFPA 13. Or you can look at the international building code because the international building code references, the NFPA standards that are in there. Now, what are we doing? ECS has developed a redundant automatic air event that you, that use to remove this trapped air. One of the benefits of our air vent is a fact is redundant and it does not require it to pipe. You have to pipe it to a drain. Also the entire assembly is FM approved and you listed it is a patented design. It only weighs eight pounds. So it was very light and it, and with the gauge that's installed on it, you can check from the floor and see that there, whether or not the primary float has failed or not. And whether it needs work. The important thing about wet pipe sprinkler systems is if you can remove 50% of the air, you can reduce your corrosion activity by 50%.

Topics: Corrosion, Fire Protection Systems, Featured Article, Video Blogs, Featured Blog, MCFP

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