Bitterly cold temperatures that swept across the United States left some water systems scrambling last January. The extreme cold froze at least a few water towers as far apart as northeastern Iowa and central North Carolina. Residents were without water temporarily as water operators worked to unthaw the water. Local media reported that another water tower in northwestern Indiana overflowed, likely due to the frigid weather.
It’s rare for a water tower to freeze over, even during the coldest winter months. There are methods to prevent such a hardship, as well as other ways to guard against any hazardous winter weather.
So, just what causes a tank to freeze? According to the American Waterworks Association a tank freezes for three reasons – static water conditions, overflow, and improper specification.
Still or static water is more prone to freezing than water that has been circulated. Fire protection tanks are more likely to have static water conditions than potable water tanks. Why? Because water stored in fire protection tanks is only used after a sprinkler system is triggered. Immersion heaters can be installed to help keep the water above freezing.
Water pumps in and out through a potable water tank throughout the day. Therefore, these types of tanks are less likely to freeze, though it’s not impossible to do so. Combine frigid temperatures with a tank that is overfilled with water, particularly during the late night and early morning hours when people are asleep, and there’s a recipe for a frozen tank.
During the coldest months, operators of elevated tanks should lower the water levels. Regular turnover helps circulate warmer water into the tank while expelling colder water. It also helps break up any surface ice that has formed.
Water is drawn from the bottom of the tank. If left uncirculated, the water at the top of the tank can become stagnant and start freezing. Potable tanks are often equipped with mixing systems that help keep the water circulating and above freezing temperatures.
Leaks or overflows in tanks are also likely to cause freezing, especially steady leaks. Trickling water can immediately freeze an overflow pipe during frigid conditions. Water pumped through an overflow pipe that’s frozen can then spill outside through the roof hatch and vent. Water is one of the few liquids that expands when it reaches the freezing point. When water inside a tank freezes, the expansion can place stress on the tank’s steel and seams. If unaddressed, the frozen tank can build up enough pressure to burst.
National Fire Protection Association Standards NFPA22-18 Section 16 provides criteria for the design of tank heating systems and tank insulation systems. Most municipal tanks for potable water are not dual design for AWWA & NFPA, however NFPA standards are often used for design specifications. Smaller diameter inlet & outlet lines in cold climates are normally included provisions for freeze protection.
Elevated water tanks are not insulated completely. Due to the size and design of the tank, along with the volume of water it contains, the tank would need to remain extremely cold for an extended time for it to freeze at all. If an elevated tank does happen to freeze, usually it’s only a foot or two of water at the top of the tank. Any amount of ice can cause damage though. Once the ice breaks free, it has enough force to rip interior ladders off the wall and puncture a hole in the tank’s container.
Ice can also scrape the interior lining, the protective coat that prevents water from interacting with the tank’s steel. Metals exposed to water are subject to becoming rusty and corroded. The interior lining helps guard against that happening, so it’s important to ensure it remains intact.
There are a few different ways to thaw out a frozen tank. Electric heaters and steam generators can warm the water enough for it to unfreeze. Of course, it requires a lot of energy and therefore money to run the electric heaters and steam generators. A cheaper method would be to wait for the sun’s rays to heat the tank enough that it unthaws.
Do you have a frozen tank? Don’t try to fix the damage yourself. Seek out a tank company like Pittsburg Tank & Tower Group for advice. A tank damaged by ice is desperately in need of a thorough inspection conducted by professional inspectors. After a tank is drained, inspectors can determine whether any holes or leaks need to be plugged. Ladders, the overflow, and piping should all be evaluated for damage. Repairs and modifications should be completed while the weather is warm.