Bolted Steel Storage Tank Construction
A bolted steel storage tank is composed of rolled steel tank panels that are connected together via bolted connections to form a vertical cylinder used for the storage of liquid and dry bulk materials. Today’s prominent bolted tank design is referred to as “RTP”, which designates its “rolled, tapered panel” construction. The RTP design features panel sizes ranging from 4-5’ in width by 9-10’ in length. RTP panel construction utilizes lap joint panel connections which require exact manufacturing tolerances. When combined with the appropriate gasket and sealant, a leak-free connection is maintained between panel connections. The tapered panel construction also holds the “inside dimension” of the tank cylinder. Each course of panels connected is called a “ring” and by connecting multiple courses of rings the cylinder is formed. A single row of bolts, along with gasket and sealant is utilized to seal each horizontal seam. Similarly, the vertical seams are sealed, but multiple rows of bolts may be required to resist design load requirements. Bolted steel tanks are available in diameters ranging from 12’-300’ diameter for liquid storage applications and 12’-48’ diameter for dry bulk hopper storage applications. Prominent bolted liquid applications for water and wastewater storage commonly use an aluminum geodesic dome cover which attaches to the top ring of the bolted cylinder, along with a bolted steel or concrete tank bottom. Prominent dry bulk storage applications commonly use a bolted steel hopper, which is designed for reliable flow/discharge requirements.
The history of bolted steel storage tank construction dates back to the late 1800’s. Riveted rolled steel tank panels were the precursor in tank/cylinder designs that required heavy plate panel construction. Bolted flanged panel tank construction, also specified as API 12B, developed in the “oil patch” territories for crude oil storage in small tank sizes ranging from 100 to 10,000 barrels. API 12B construction utilizes an external flange connection for the horizontal seam which is called a chime connection. Specification for API 12B bolted tank construction remains relevant today only for its original intended use. In hydrostatic applications of water and wastewater, this product has a history of developing continuous leaks in the field. Flat panel construction is another bolted tank design that does not maintain a tapered panel design, which allows variance in the 4 corner panel lap connections. Flat panel designs may be used in “light duty” commodity storage applications, but special care is warranted during field construction to produce a leak free cylinder. Corrugated steel panel construction is another alternative bolted tank design typically used in the storage of “free flowing” grain products. By forming corrugations in the bolted tank panels, additional panel strength can be realized. Corrugated construction maintains an adequate performance history in long term grain storage, but should not be used for “continuous process” dry bulk storage applications.