Nitrogen Generators and Guided Wave Ultrasonic Testing (Video)

When you suspect corrosion in your sprinkler system pipes, or want to confirm your system is corrosion free, guided wave ultrasonic testing is one way to detect its presence. Once detected, you are then able to seek out a solution to replace damaged areas and pursue ways to prevent corrosion in the future. Nitrogen generators absorb excess moisture and get rid of oxygen in your pipes, cutting down the possibility of corrosion. Watch the video below as Lee Kaiser explains ultrasonic corrosion and prevention methods.

Video Transcript

Guided Wave Ultrasonic Testing

Lee: "I want to talk about locating the issues within the system. When I realized I have corrosion problems, NFPA 25 Chapter 14 for Internal Inspection Investigations tells us that we need to determine the extent of the damage. If I don't want to take my system apart to do that, one way we can do it in a non-destructive manner is with a technology called ultrasonic localized guide wave testing. Ultrasonic testing is one way for us to do a non-destructive test to determine the level of corrosion inside the pipes as well as see if there is any residual water sitting inside the pipes.

That can be done in any operating space. It's a non-destructive method, all done from outside the pipe. It's safe around sensitive equipment, and besides setting up the ladders it doesn't disrupt daily operation. At the end you wind up with a map of your sprinkler system and knowledge of the severity of the corrosion within the system so you can determine where your problem spots are and only focus on replacing those pipes in the problem areas. By the way, this is an NFPA compliant method.

This is a picture of one of the maps out there by one of the ultrasonic testing companies. You see they use a green light, yellow light, red light system. Green light means pipes are okay, yellow light means you've got some corrosion in there, and a red light means you need to replace those pipes or that section of pipe.

Basically, the tester or technician running the test will come out and put this device on the pipe. It will measure around the radius or half the diameter of the pipe and tell you what's going on. When he looks at his meter and sees that there's a problem, then he shortens the spacing that he's taking tests. Normally they're taking tests about every 20 feet, but when they see there's a problem they'll shrink it down to 10 feet down and 5 feet to get an accurate map of what's going on in that pipe you can figure out exactly what pipes you need to replace. If you don't have this knowledge and just replace the whole thing, you could be spending a lot more money than needed, versus maybe just replacing 60 some feet of the worst pipe.

Compressed Nitrogen

One of the solutions, as I mentioned, is to use compressed nitrogen instead of compressed air. Nitrogen generators or compressed nitrogen bottles are one way that we can charge a system with nitrogen. Nitrogen is a very dry gas that will actually absorb some of the trapped moisture in the pipes. After doing a full flow trip test I've drained as best I can, I still have some water sitting in there. Over time, systems equipped with a nitrogen generator will dry those systems out because the dew point of the nitrogen is so low.

Once I remove oxygen it breaks that corrosion triangle and stops the corrosion process. Nitrogen affects the bio bugs, the organisms can't live in a nitrogen rich environment and they die off. Nitrogen is an inert gas and we're breathing nitrogen right now; normal air contains about 70 percent nitrogen and we're all inhaling and exhaling nitrogen.

The way that we provide nitrogen to systems is a nitrogen generator. They either install inline or replace a compressor system providing compressed air to your sprinkler system. Between the air compressor and the maintenance device, they require 125 PSI of dry, clean, compressed air to make the nitrogen and after that it supplies a continuous stream. Most of the systems today run at 98 percent purity. There are some specifications from 6 or 7 years ago that require 99 percent purity and some that required 95. The industry has determined that 98 is the sweet spot, not too little not too much, and can be made economically to stop corrosion in its tracks.

For existing sprinkler systems, such as the one you're asking about, the goal is to evaluate the degree of the corrosion problem. We want to know how bad the pipes are first, replace pipes as necessary, and then install the nitrogen generator so that the system doesn't get worse."

Audience: "What about initial installation?"

Lee: "Well, initially we suggest two things; don't install galvanized pipe anymore; just use black pipe because that performs better. Even though the industry used to think galvanized was the way to go, it really isn't. Systems fail faster when they're installed with galvanized pipe and then just specify a system from the get go.

We're seeing that and feel like we need to educate consulting engineers about that. It used to always be black pipe, even dry systems. Now we're going back to black because the corrosion action inside the pipe is more distributed. Instead of focusing on spots where the galvanized coating is not consistent, so little pits in there or anytime we roll groove a pipe and that roll grooving process breaks the inside of the pipe. Those are places where we get a lot of corrosion."

That concludes our third video in our four-part chapter on fire sprinkler leaks and corrosion. Visit the index at the bottom of this page to view the previous parts as well as all the other videos in this series. If you would like to learn more about a broad range of fire protection topics, register for a Lunch and Learn by clicking the button below.