Microbiologically Influenced Corrosion
In addition to generalized corrosion, some sprinkler
systems have dealt with microbiologically influenced
corrosion (MIC), which is corrosion that is promoted
by bacteria and other microorganisms.
Recently, MIC has become a hot topic when considering corrosion in fire sprinkler systems, and it had a
major impact on how facility professionals went about
addressing corrosion. “Everyone was jumping to the
conclusion that if you had corrosion in your wet-pipe
system, it had to be MIC. A lot of MIC test kits were
sold, but the results were not entirely conclusive and
subject to much interpretation,” explains Harrington.
But once he started looking into cases where
there was a suspicion of MIC, it was much simpler.
Harrington notes, “In every single case, the cause was
proven to be the existence of trapped air with the water
resulting in oxygen corrosion.” In Harrington’s experience, MIC has only exacerbated an already existing
oxygen corrosion problem.
Although countless systems are needlessly treated
for MIC, that does not mean MIC does not exist.
Finding out if the corrosion you are grappling with is
MIC-related can be frustrating. It requires two tests:
the first to test the source water that fills the system
and the second test of the water near the site of corrosion in the system.
For definitive results, these tests require accurate
and impartial interpretation, which can be difficult.
Consequently, proving that MIC is the primary cause of
corrosion with a high degree of certainty is not easy.
Instead of this significantly more expensive MIC
investigation strategy, Harrington suggests that a screen
test should be conducted first to identify whether
trapped air in the piping is causing oxygen corrosion.
This is relatively easy to do with a careful external
inspection of the system near the site of corrosion to
see if the piping orientation might trap air.
If it is, remove several sections of pipe in these loca-
tions and visually inspect for signs of oxygen corrosion
with an expert. If you determine that the likely cause of
corrosion is oxygen, modify the system by reorienting
the piping to eliminate the sections that can trap the
largest volume of air and install a single air vent valve
in the most strategically effective location, as NFPA 13
“You can spend money on MIC testing and still not
have definitive proof that MIC is the primary cause.
Then you have to decide whether you’re going to spend
the money on a MIC mitigation system or seek help
elsewhere,” explains Harrington. “The investment in
MIC testing and treatment may not return because if it
When it comes to piping material, consensus can
be difficult to find. Galvanized steel can corrode once
the zinc from its composition becomes depleted. Black
steel works well in systems with inert gas systems,
but it can corrode easily where there is vertical piping
or wherever oxygen can get trapped. CPVC pipes do
not corrode because they are not metal, but extreme
temperatures and other contents like oils in the water
can weaken the plastic.
“There’s no single material that is bulletproof. All
materials have their Achilles heel, and it’s just a matter
of being aware of it and employing proper installation
practices,” Pfaendtner says. Consult with a professional
on what material for piping will work best with your
building, as the location, utility, building shape and
more are all dynamic factors in the durability of pipes
in sprinkler systems.
As you look at your own system, you might find that
if you are able to locate areas of corrosion before they
become major problems, you can replace the problem
areas instead of the entire system. But these problems
often persist, so the answer may be in solutions like
nitrogen supplies or water treatment. To truly ensure
safety, you need to properly plan and invest in a system.
Faulty fire sprinklers help no one, so staying ahead of
corrosion can save money, property and lives.
Justin Feit firstname.lastname@example.org is assistant
editor of BUILDINGS.
IN CONTROLLED TESTS OF SPRINKLER PIPING, researchers found that nitrogen generators are effective in deterring corrosion. After letting
a series of varied pipes sit, the researchers cleaned the interiors of the piping to find that nitrogen considerably slowed down the corrosion
penetration rate in both black and galvanized steel.