New Trends in Corrosion and Freeze Protection for Resilient Fire Sprinkler Systems

How can you prevent corrosion and freezing in fire sprinkler systems? That has long been a question central to code requirements and new product development.

Recent innovations have presented a few possible answers to that question. Air vents, self-draining auxiliary drains in heated cabinets, and flood elimination devices, can protect fire sprinkler systems against the common pitfalls of corrosion and freezing.

Adopting Code to Prevent Corrosion in Wet Systems

Wet pipe fire sprinkler systems contain the perfect storm for corrosion. Water, metal, and oxygen from trapped air react to corrode the pipes.

Corrosion can cause pinhole pipe leaks that result in expensive property damage. But the bigger concern? Life safety.

Corrosion can also cause obstructions that impair system performance. An impaired system puts lives at risk.

NFPA 25 requires periodic internal inspections to check for obstructions to prevent this.

Ironically, those inspections increase the rate of corrosion. By draining and re-filling the system, they introduce fresh water and more trapped air.

If the check for corrosion-caused obstructions leads to more corrosion, how can you stop the cycle?

Long-term studies by the National Fire Prevention Association (NFPA) and Factory Mutual have found that trapped air in wet pipe sprinkler systems is a major contributing factor of corrosion.

Venting any amount of air reduces the amount of resulting corrosion. Based on those studies, the 2016 edition of NFPA 13 adopted the requirement for air vents as part of the main text.

The code requires a single manual, automatic, or other approved air vent near a high point on each metal wet pipe sprinkler system.

Adopting Devices to Prevent Corrosion

AGF's Model 7910 manual air vent

Manual air vents are the most economical way to fulfill code and prevent corrosion. They vent air while a system is being filled.

Contractors open manual vents while filling the system and close them when water reaches the vent to prevent overflow. This requires an extra person to watch the valve and close it at the right time.

AGF’s Model 7910 includes a ball check to remove the need for an extra person. When the water reaches the valve, the ball check will prevent it from overflowing. When the system is full, close the vent.

Automatic air vents are the most effective at preventing corrosion because they don’t only vent air while the system fills. They automatically continue to vent air as the system settles or internal pressures fluctuate.

Some versions currently on the market have a history of spitting. So, they include redundancy, drain lines, or drip pans. These are not required by code.

Model 7930 end cap automatic air vent

AGF designed valves to address the needs of wet sprinkler system vents. Their PURGEnVENT products have addressed these flaws. PURGEnVENT automatic air vents also come with many installation options. That makes retrofitting them to existing systems simple.

Some people think you can use an inspector’s test valve as an air vent. But, it’s not an effective option for air venting.

An inspector’s test and drain valve sit at the low point of the system to facilitate drainage. That means they can’t sit at the high point to vent air.

Plus, when the system is filling, the drain legs fill before the main pipes. The inspector’s test valve gets cut off before most of the air exhausts.

New Innovations to Prevent Freezing and Flood Damage

Unexpected freezing weather in the Southeast this year proved that freeze damage can devastate a facility. Freeze prevention is vital for fire sprinkler systems.

NFPA requires auxiliary drains on dry pipe systems. These drains collect condensation that accumulates in the pipes.

In freezing temperatures, drains that have not been emptied can freeze and break. This trips the dry valve and sends a fully pressurized flow of water to the broken drain.

A fully open, one-inch pipeline can spill out 50 to 70 gallons of water a minute (depending on available system pressure). That flow can cause thousands of dollars in facility damage. Plus, there’s the system repair cost, building occupant displacement, and additional owner liability.

To prevent freezing altogether, consider upgrading the auxiliary drains.

Water detector alarms on drum drips sends an alert when drains need maintenance. With proper maintenance, this is a simple way to prevent freezing.

For more extensive freeze protection, facilities are choosing heated auxiliary drain cabinets. These locking cabinets are insulated and contain thermostatically controlled energy-efficient heaters. Some of these cabinets even include features that allow them to self-maintain or operate automatically.

Stopping the Flood

Constant vigilance and the required maintenance to prevent a freeze and break might not be an option. In that case, consider a product designed to minimize the impact of a broken auxiliary drain.

Flood eliminator installed at the inlet of an auxiliary drain.

The Flood Eliminator stops the flooding that would result from an auxiliary drain failure.

As mentioned before, a broken auxiliary drain can spill 50 to 70 gallons a minute. Most often, systems break when temperatures dip below freezing in the middle of the night. So, it usually takes time for someone to respond to a failed system and come shut it down.

Even if it only takes ten minutes, that means 500 to 700 gallons of water have flooded the facility in that time.

Flood elimination devices sit above the inlet of the auxiliary drain and do not affect normal auxiliary drain operation.

When the fully pressurized flow triggered by a tripped dry valve activation hits one of these devices, it senses the sudden pressure. Then, it restricts the flow of water to only eight ounces a minute. In ten minutes, that would be less than a gallon versus the up to 700 gallons from an unrestricted flow.

The auxiliary drain will need repair and the system reset, but this minimizes the damage to the building and inconvenience to tenants.

In Conclusion

Corrosion and freezing temperatures threaten fire sprinkler systems in facilities around the world. Luckily, new innovations bring solutions like air vents and auxiliary drain accessories to the market.

Many of these products are easy to retrofit onto existing systems. So, the benefits are not limited to future systems. Although corrosion and freezing temperatures are nothing new, these innovations could bring a new chapter of simplified maintenance and increased reliability to wet and dry fire sprinkler systems.

A version of this article was originally seen in the June 2021 issue of Plumbing Engineer Magazine.