Modern technology allows water tank inspections without taking the tank out of service
By Erika Henderson, Pittsburg Tank & Tower
Water tank failures can be prevented but only with proper care and maintenance. When minor deficiencies go unnoticed, they often evolve into major structural deficiencies. Getting a tank inspected is the first step to preventing damage and extending the life of the water tank. The list of items, deficiencies and code updates to look for during an inspection can easily become overwhelming; therefore, a licensed professional tank inspection company should be contacted to conduct these inspections.
There are many different types of tanks and each should be designed and inspected for its specific purpose. The two main types of water tanks are potable and fire protection. A fire protection water tank is used only for fire protection and must follow all National Fire Protection Association (NFPA) and Occupational Safety and Health Administration (OSHA) regulations. A potable water tank is used for drinking water and follows American Water Works Association (AWWA), Environmental Protection Agency (EPA), and sometimes NFPA standards because a portion of the water is also reserved for fire protection. Other state specific standards may also need to be followed.
Tanks should also be designed and inspected not only for their specific purpose, but also for the area where they are located. Water tanks located above the isothermal line or in any area that may produce freezing temperatures must also be protected from freezing. A frost-proof drain valve is needed in these locations, and some valves need to be inspected daily during the winter months to make sure they have not frozen or cracked. A frost proof drain valve is a double valve construction that allows the inner chamber to drain completely before the outer valve is closed. Valves and controls should also be checked regularly to ensure function. Valve location can also affect how often they should be checked. Flapper valves on the overflow should move freely because sometimes leaves and paint chips can get stuck in the overflow pipe or screen. If the overflow pipe were to become clogged, the water level would back up and continue to rise in the tank, causing the tank to overflow the access hatch or vent. Should the vent become clogged or frozen as well, pressure could build, causing the tank to eventually burst or collapse. The vent should be pressure-vacuumed and frost proof with the screens clear of debris or other obstructions. Most important, fire protection tanks must be heated, and according to NFPA 22, “the heating shall be of such capacity that the temperature of the coldest water is maintained at or above 42 degree Fahrenheit during the coldest weather. The coldest weather temperature shall be based on the lowest mean temperature for one day.” This can be achieved by heating and insulating the tank, and it can be monitored by installing a low-water temperature alarm. NFPA 25 contains several recommendations on valve inspections and a helpful chart that lists when each type of valve should be inspected.
In the past, the only way to inspect the interior of a water tank was to take it out-of-service and drain. This method is still used today, however, it requires the loss of purchased water and the expense associated with refilling the tank. It leaves the system vulnerable with no water or fire protection reserves. Tank owners and inspection companies are put under stress due to the strict time constraints of having the tank out of service, and caution must also be taken when draining a tank. If the water is drained too quickly, it can create a vacuum and cause serious catastrophic damage.
Whenever a tank needs to be drained for an inspection or isolated from the system, a pressure relief valve should be installed. If over-pressurization occurs, the valve temporarily pops open thereby relieving the pressure. The gate valve that isolates the water tank should be located and the relief valve installed on the fire hydrant, making sure that the location has good drainage for the excess water. The pressure in the system should be closely monitored, and the relief valves should be checked and adjusted if necessary. After the tank is drained, the qualified inspector enters the tank and inspects every aspect. The floor and foundation are checked for settling, stability and leaks. The thickness of the steel and corrosion level are tested. Ladders, platforms and lights will be checked for safety and prevention of vandalism and unauthorized access into the tank. Overflows, manholes, and vents are inspected to make sure they meet all required codes and work sufficiently. After the drained inspection is complete, tank owners should confirm the check valves are working properly and shutting off at appropriate times. Conduct a simple hydrostatic pressure test by shutting off the valve and filling the tank with water. Turn the pumps off and see if the check valve opens at the correct time. The float valve and gauge can be tested at the same time. When the tank fills, make sure the float valve moves properly and closes, and the check valve opens to allow the tank to drain.
Later, tank companies decided to incorporate diving operations to make tank inspections more convenient for the customers. Tanks do not have to be drained and no water is lost with the diving inspection operation. Sometimes under-water cameras are used to photograph areas of concern, and the diver can touch parts of the tank to determine its condition. This method is time saving, but it also brings with it a liability. A confined space permit is needed and lockout/tag out procedures are required. The diver’s safety and health are at risk if the diving equipment fails or the diver experiences problems. Sanitation is also a concern when something enters the tank.
Now, modern technology allows tank inspections to be completed without downtime, liability or water loss by using a ROV (Remote Operated Vehicle). The ROV inspection does not require draining the tank. Lockout/tag out procedures and confined space permits are not needed because no one enters the tank. The ROV is equipped with lights and a color camera controlled by qualified inspection personnel trained to use the equipment. The ROV is disinfected with a solution. Then, it is lowered into the tank by a tether and moved about by thrusters and propellers, so sedimentation is not stirred. The ROV has front and rear propellers that allow it to move forward or backward. The vertical and horizontal thrusters allow it to stop or turnabout easily. This allows live viewing of the inspection through a ground monitor as the inspection is performed. The ROV should include a DVD of the inspection with photographs and recommendations. All aspects of the tank should be inspected for structural, safety and coating conditions in accordance with NFPA, AWWA, OSHA and EPA standards. Vents, screens, manways, overflows, ladders and drain valves are also inspected to prevent unauthorized access by people, insects or animals. A written inspection report includes a detailed evaluation, photographs, recommendations of needed repairs, code updates, and a detailed cost estimate for each item.
Water tanks must be inspected and cleaned periodically to maintain an optimal system. Many water tanks accumulate sedimentation on the floor or bowl of the tank. Removing sediment prevents sanitation problems and other complications that may result from sludge build up. A fire sprinkler system that pumps sediment and rust instead of water is not effective. The loss of a few sprinkler heads could result in a system failure, causing loss of property and life. Two options are possible for cleanouts, drained or robotic. If a drained cleaning is requested, then the sediment is removed and placed in owner-supplied containers. If a robotic inspection is requested, then the robot is lowered into the tank and the sediment is suctioned out of the tank via hose and brushes.
Thanks to modern technology and innovative services, tank inspections and cleanouts can be performed without draining or taking the tank out of service. Tank inspections can be stress free and convenient. The inspection report alone is not enough to ensure a safe and healthy environment to store water, but it does provide crucial information needed to do so.
Items and deficiencies listed in the inspection report must be addressed and corrected to maintain a safe and optimal operating tank.