Anhydrous Ammonia Storage Tank Location and Design
Stationary storage tanks for anhydrous ammonia are regulated by the U.S. Dept. of Labor and must conform to the requirements of 29CFR1910.111. They are built in accordance with the ASME Boiler and Pressure Vessel Code and are rated for 250 psig.
Tanks should be located in an area, preferably outdoors, where they will not be exposed to damage by vehicular traffic, however, access to within 50 feet is generally necessary for tank truck delivery. The area should be clear of debris, weeds or any combustible materials.
If the tank is located where summer sun conditions are severe, provisions should be made for sun shielding. In some area, local codes require diking. Check your local codes.
Tanks should be mounted on concrete, masonry or structural steel supports and on firm concrete or masonry foundations. All foundations should extend below the frost line.
Refer to ANSI K 61.1 for additional information.
In the event of an emergency, access to the tank must be provided. If the tank is fenced in, two to four feet clearance is recommended as a working area for maintenance purposes. Fenced in tanks should also have two means of egress for emergency escape.
All pipe and hose connections to the tank are protected by excess flow valves to prevent massive leakage in the event of a catastrophic line break. Relatively high flows are required to cause these valves to close so it should be noted that a downstream break may not always result in sufficient flow to close the valve.
Pressure gauge connections and the 85% outage gauge are not protected by excess flow valves but they do have a .054" restriction to limit flow. Tank pressure gauges are also equipped with isolating valves which can be closed off in the event of a gauge failure.
The tank is equipped with a dual safety relief valve system consisting of two safety relief valves mounted on a three-way valve. The design of the three-way valve permits shutting off one or the other, but not both, of the relief valves and allows replacement of either of the relief valves without emptying the tank. Either relief valve alone is sized to adequately protect the tank.
Different designs of three-way valves have been used. The “Shank” design has a handwheel. Facing the handwheel, to shut off the right hand safety, turn the hand wheel counter clockwise. To shut off the left hand safety, turn the wheel clockwise. The handwheel should be left in full counter-clockwise position so that the valve stem packing and the right hand safety relief are isolated from the tank pressure.
The “Frick” or “Henry” design valves are of the “in-line” type and may have a conical cap cover in the valve stem. If the valve is of this type, the valve stem has flats on it and a wrench must be used. Use caution when removing the cap as it may be under a slight pressure. Turning the valve stem clockwise will shut off the safety relief furthest from the valve stem. Turning the stem counter clockwise will shut off the safety relief nearest the valve stem. The valve should normally be left in the full counter clockwise position so that the valve stem packing is isolated from the tank pressure.
Tank content is determined by means of a float gauge which reads in percent of the total tank capacity. The gauge dial is usually on the top of the tank; however, it may be located at one end. When mounted on a 1,000 gallon tank and reading 60%, the tank would contain 600 gallons. At 5 lbs. per gallon, this would be equivalent to 3,000 lbs.
Do not confuse this gauge with the pressure gauge. The pressure gauge would read the same whether there is a 200 gallons in the tank or 800 gallons.
Recommended Sources of Information on Anhydrous Ammonia