Sprinkler System Piping
The Arteries

Materials Allowed

NFPA 13 Chapter 6 permits only specific listed pipe materials. In practice you will see four of them:

MIC — The Hidden Killer

Microbiologically influenced corrosion is the number-one cause of unexpected dry system failures. A colony of anaerobic bacteria establishes itself in stagnant, low-oxygen pools of water in the pipe and releases acidic metabolites that attack the steel from the inside. The pipe exterior looks fine; the interior has pinhole leaks and tubercles that reduce flow and eventually rupture.

MIC is suspected when: pinhole leaks appear in a system less than 10 years old, dry systems fail to maintain air pressure without any obvious cause, or internal inspection reveals black nodules or orange slime. NFPA 25 §14 requires an obstruction investigation whenever any of those findings occur.

NFPA 25 Annual Inspection

§5.2.2 requires an annual inspection of piping from floor level. Inspectors look for:

• External corrosion, rust streaks, and leaks at fittings.
• Mechanical damage, especially in warehouses and loading docks.
• Misalignment or sagging pipe (a sign of failed hangers).
• Loading — storage, wiring, or decorations hung from the pipe or within 18 inches of sprinkler deflectors.
• Painted-over pipe, frozen pipe insulation failure, and missing escutcheons.

References