Advice to Prevent MIC in Sprinkler Systems?

6/30/2026

What are others doing to combat Microbiologically Influenced Corrosion (MIC) in their sprinkler systems?

I'm dealing with a project where MIC has been found in a nearby building/system.

Doing research, nitrogen appears to be a popular treatment method, but I've read sprinkler-based articles that it's not effective. I also noticed that the NFPA 13 2025 edition removed the treatment options previously in paragraph 5.1.4.1.2. Additionally, the client does not want the monitoring option (item 3 of 5.1.4.1.2, 2022 edition).

Any advice on how to prevent MIC here?

Thanks in advance.

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11 Comments

Pete H

6/30/2026 06:05:56 am

Have you looked into General Air Products' "Vapor Pipe Shield"?

It is supposed to prevent significant amounts of corrosion and be an improvement over nitrogen.

Wes

6/30/2026 08:14:59 am

I'd be curious to check out about articles on nitrogen not being effective. It has a track record, is used even by larger users and FM recommends it.

If you remove the oxygen, the corrosion doesn't happen. Nitrogen might still be viable here.

Brian Gerdwagen

6/30/2026 09:09:28 am

Not all corrosion, even microbial, is aerobic. A lot of the corrosion found is anaerobic and oxygen does not play a part.

Rick link

6/30/2026 08:18:00 am

Have you considered doing the system in copper. That eliminates the mic problem. Better hydraulics. A little cost up front but saves a ton of money on system maintenance and truly gives you a 20 year no corrode system.

6/30/2026 08:22:02 am

If it is a wet pipe system, eliminate trapped air.

Also, here is an FM Technical Report on this subject:
https://www.fm.com/-/media/project/publicwebsites/fm/files/resources/research-technical-reports/p14180.pdf

6/30/2026 08:25:36 am

Flush the system, add vapor pipe shield, if it's a wet system add automatic air vents at system high point(s). Nitrogen is only effective if it can be maintained at 98% or higher which is difficult to achieve (especially in older systems) which is why there's growing concern with it's application.

Wes

6/30/2026 08:37:25 am

The downside I'd have with Vapor Shield is having to add an RPZ to the system - but the viability concern is there too - getting coverage in all the smaller diameter branch pipe. Not saying nitrogen should go everywhere, at all. If the system is small enough, the cost of nitrogen might be more than just replacing the pipe or portions of the system regularly. At least with the nitrogen systems you can see the % nitrogen actually achieved (I think all vendors do that now?). I could be wrong but I dont believe the Vapor Shield has a way to monitor/prove that it has coverage in those branch pipe dead ends.

Glenn Berger

6/30/2026 08:32:17 am

The issue concerning N2 stems from the difference when using 95% design vs 97% and above design levels.

An issue that has not been mentioned above is know the water source and if needed treat the water prior to entering the system.

Wes

6/30/2026 08:38:51 am

Right - for a MIC concern specifically this could be the easiest/cleanest route if that's viable. Or even start with that and then test for MIC periodically?

Dan Wilder

6/30/2026 10:03:03 am

Living in the desert, our water quality is very poor (lots of chlorine, calcium, and other hard water aspects) and we deal with many issues generally linked with the water quality. However, there are a lot of other factors that play into things.

Firstly, in my experience, we don't even test the water anymore (we will if the owner requests, but that money is better spent in other remediation efforts). The testing has always come back positive for signs, features, and chemicals linked to Corrosion in general, and those reports use ambiguous language like "..can be attributed to..". "..often found as a result of...", "...may be a result of..." and I can say that I have never had a test come back negative.

While the test was positive, is the owner seeing issues? Are there pin hole leaks (are these at welds/threads, pipe seams)? Is there slime or other large growths (pipe slope or excess moisture in the system)? Does the piping have tubercules causing a restriction of the ID of the pipe? Is there trapped air in the system (wet - are there air vents) or trapped water (aux drains)? Is everything sloped correctly (dry)? Are the flushing procedures being followed? What schedule is the pipe, how old, origin?

Our typical go to is N2 inerting and high point vent additions. This resolves most of the issues within a couple months (the draining and filling of systems will typically create some short-term spikes in issues). We will put signage for other companies to make sure they perform the same inerting when refilling the system. We do not push chemical methods due to the RPZ requirements and its effect on the hydraulics.

Jose Figueroa

6/30/2026 10:54:43 am

The latest update from FM is that MIC is an overrated source of corrosion. Consider MIC only as a contributing factor—prioritize oxygen control (vents + nitrogen where feasible), thorough inspections, and physical removal (replacement) over chemical treatment. This advice is conservative and evidence-based, focusing on long-term system reliability without creating new risks from uneven chemical application.

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