Storage Tanks

On February 10, 2014 WZZM 13 staff reported, “GRAND HAVEN TOWNSHIP, Mich. –Hundreds of gallons of water and freezing temperatures are proving to be a messy mix for Grand Haven Township leaders. A leak at the township’s water tank has created ice formations on the inside and it is taking weeks to melt it away.”

 

Similar situations are occurring everywhere nationwide. Georgia, South Carolina, and even Texas have been hit this winter with unusually low temperatures creating serious problems for many people, including tank owners whose tanks are not insulated or heated. Generally, tanks located below the isothermal line maintain average temperatures above freezing. An isothermal line is a line on a map or chart that links points of equal or constant temperature. The NFPA 22 contains a map of the United States that illustrates the lowest one-day mean temperatures and tank owners may refer to it when determining the location of their tank on it. “The coldest weather temperature to determine the need for heating shall be based on the lowest mean temperature for one day.” (NFPA22-16.1.2.1) However, weather cannot always be predicted accurately as witnessed this winter, and sometimes temperatures in these areas marked below the isothermal line do experience prolonged freezing temperatures. Therefore, a good rule of thumb is to maintain tank water temperatures above 42 degrees F.

 

When the water temperature inside a tank falls below freezing for extended periods, serious problems and tank damage can occur. Ice crystals can gather on piping, ladders and other attachments and along the water’s edge. As ice accumulates, the extra weight increases and can pull attachments from the shell creating holes or other damage to the tank. The interior coating system is in constant jeopardy of damage from scratches, tears and punctures while ice remains in the tank. Control malfunctions can occur with water level conductors and cathodic protection anodes that are not freeze proof can be damaged. But, the interior is not the only part of a tank at risk for damage. The outside of a tank can also receive damage. Snow and ice that accumulates on the roof and outside attachments can exceed the tanks design criteria, increasing the chances of damage and tank failure. This accumulation can also clog vents that are not vacuum pressured and frost proof. If pressure is trapped inside the tank, the shell or roof could collapse or buckle. Pipe inside dry risers should be insulated to prevent the pipes from freezing. Other piping should be large enough and placed in the appropriate locations to prevent freezing as well.

 

According to NFPA 22, “tanks subject to freezing shall be heated.” (16.1) Heating and insulating the tank can help prevent tanks from freezing, and the temperature can be monitored by installing a low-water temperature alarm. Tanks can be heated several ways- steam, hot water, or immersion heaters. The type of system currently in place could determine the most cost effective heating option. For example, if a boiler system is already in place, then heating the tank by steam may be desirable. Steam is a closed system and as stated in NFPA 22, “should consist of a cast-iron or steel shell where water circulates through the steam tubes or coils of brass or copper. Galvanized steel or iron steam tubes are not advised because of their more rapid depreciation and poorer heat-transfer qualities.” When an open circulating system is desired, hot water may be used to heat the tank. Hot water placed in the tank rises to the top. Cold water from the bottom is taken and heated, then placed back into the system. When these methods of heating are not convenient most tank owners install electric heaters and insulate the tank.

Insulation can minimize or eliminate the need for heating energy for freeze protection. Energy costs can be reduced by as much as 90% when insulated.  Spray and panel are two forms of insulation that may be used to protect a water tank from the destructive outside elements. Each form of insulation requires the tank surface to be power washed with an antifungal solution and hand tool cleaned to remove loose coating material. With spray insulation, a polyurethane insulation is applied to the tank and an acrylic waterproofing coating that protects against ultraviolet deterioration is applied. With panel insulation, rods are welded on the tank to secure the panels and prefabricated vertical standing seam panels are attached using galvanized steel cables properly tensioned with turnbuckles. All joints are caulked and all roof seams are enfolded in the downslope direction. The interior paint is touched up, where damaged from the welding of rod holders on the tank. Today, with all the conservation and LEED requirements occurring, the panel insulation and immersion heater package is the standard in the industry.

 

Water tanks must be protected from the outside elements and certain precautions are necessary to prevent damage caused by snow, ice and freezing temperatures. Failure of any component on a tank could have dire consequences, especially during extreme weather. Pipes, valves, controls, and heating elements should be checked regularly to ensure accurate functioning. During the winter months, these may need to be inspected daily for signs of frozen, cracked or damaged areas. Contact a professional tank company immediately if ice has formed inside the tank. Do not attempt to thaw the tank without professional help-further damage and even tank rupture could occur. Please contact Erika Henderson or Don Johnston at [email protected] or 270-826-9000 ext. 228 to answer any questions concerning water tanks.