Call · (314) 432-1377
Email · info@ecscorrosion.com


Galvanized Pipe vs. Black Steel

Galvanized Pipe Code References

FACT: NFPA 13 does NOT require the use of galvanized pipe in dry or preaction sprinkler systems, except for Control Mode Specific Application (CMSA) sprinklers - formerly 'Large Drop' sprinklers

FACT: FM Global permits the use of black steel pipe in dry and preaction sprinkler systems when the system is filled with an inert gas, such as nitrogen

FACT: The 2013 edition of NFPA 13 no longer provides a hydraulic advantage for galvanized steel pipe (Table 23.4.4.7.1)

FACT: The Unified Facilities Criteria does not allow galvanized pipe in preaction fire sprinkler systems

Galvanized Pipe Corrosion: In fire sprinkler systems galvanized pipe fails 3-4 times faster than black steel pipe, yet material costs are at least 30% greater.

 

“New dry or preaction systems can develop through-wall corrosion pinhole leakage within 2-3 years after initial installation, due to residual water causing corrosion in galvanized steel pipe.” – FM Global Research Technical Report, July 2014

Does your galvanized sprinkler pipe look like this? This is not MIC, material defect, or corrosive water. This is classic oxygen corrosion. The zinc layer has been breached in areas where trapped water is present resulting in the orange, red, or brown iron oxide that is indicative of corrosion of the base metal.
Galvanized Pipe Corrosion

Galvanized Main Corrosion

Galvanized Pipe Corrosion

Galvanized Pipe Tubercles

Engineered Corrosion Solutions can save your failing sprinkler system. Existing dry and preaction fire sprinkler systems equipped with galvanized pipe can be salvaged with surgical pipe replacement and a nitrogen-based corrosion control system. Our extensive testing and inspection activity in existing sprinkler systems has shown that 80% of system piping does not need to be replaced due to the highly localized nature of corrosion At ECS we recommend black steel pipe under a nitrogen atmosphere for all new dry and preaction fire sprinkler systems. This configuration is allowed by FM Global Data Sheet 2-0. Learn more about the ECS Protector Nitrogen Generation System for fire sprinkler systems.

Why is galvanized pipe a poor material for fire sprinkler systems?

Zinc owes its high degree of resistance to atmospheric corrosion to the formation of insoluble basic carbonate films. Environmental conditions that interfere with the formation of such films may attack zinc quite rapidly. The important factors that control the rate at which zinc corrodes in atmospheric exposure are:
  • the duration and frequency of moisture
  • the rate at which the surface dries
  • the extent of industrial pollution of the atmosphere
In a persistently wet oxygenated environment galvanized pipe will corrode faster than black steel because the protective carbonate film (ZnCO3) that prevents oxidation cannot form under water. The rate of drying is also an important factor because a thin moisture film with higher oxygen concentration promotes corrosion. galvanized pipe corrosion Suggested Article: Exploring Galvanized Pipes Failures in Dry and Preaction Fire Sprinkler Systems

History of Galvanized Pipe in Fire Sprinkler Systems

Galvanized steel is used in a variety of industrial applications to provide protection against atmospheric oxygen corrosion. Common applications for galvanized steel include highway guard rails, flag poles, corrugated roofing and hand railings. In these applications, the zinc coating on the black steel substrate provides a protective barrier to oxygen corrosion of the steel. Galvanized steel piping was initially recommended for use as the material of choice for dry pipe fire sprinkler systems more than 20 years ago to prevent the formation of iron oxide (hematite) corrosion by-product that occurs as the interior surfaces corrode in black steel sprinkler piping. It was reasoned that excessive amounts of iron oxide can build up within the piping and create an obstruction risk that might prevent the function of the fire sprinkler system sprinklers. In 2008, as part of the Failed Pipe Analysis that is routinely performed by ECS on fire sprinkler pipe samples, a pattern of highly localized corrosive attack was noted in many of the galvanized fire sprinkler pipe samples that were analyzed for clients. In several installations, galvanized failures in dry pipe applications were occurring within as little as 12 months from initial installation.

Conclusions

It cannot be stated any more clearly. Galvanized steel piping will corrode quickly under the environment that typically exists in dry and preaction fire sprinkler systems. ECS recommends against the continued use of galvanized steel piping in ANY fire sprinkler application for the following three reasons: 1. Galvanized steel piping is more expensive than regular black iron steel piping. The raw piping cost comes at a 30 – 40% cost premium. When there is water present inside the piping, the galvanized coating will eventually be breached. Once the breach is created, the exposed uncoated mild steel will corrode at a much faster rate than the rest of the piping where the galvanized layer remains. The end result is a pin-hole leak that forms much faster than it would in non-galvanized black steel. 2. The hydraulic advantage that is gained by using galvanized steel piping will be lost as the zinc metal surface is deformed and pitted by corrosion. In actual performance, the corroded galvanized steel piping will not accurately reflect the theoretical hydraulic calculations that were performed during system design. 3. Galvanized steel piping creates a false sense of security that the system is completely protected from corrosive attack.