Environmental Engineering Reference
In-Depth Information
storage material chosen. Many tank materials have been tested and under-
gone industrial experience. The consensus in the industry is to use concrete
and steel with various insulation materials.
Steel is optimal for very large storage tanks in which large volumes of
fluid exert high pressure on the storage container; appropriate design is
critical. Steel tanks have high strength and can be welded on site. The
interior and exterior of a steel tank must be coated to ensure corrosion
resistance. Concrete is recommended for unpressured systems. It is a
low cost material capable of storing large volumes contents. Care must
be taken with the surface treatment to keep fluids from seeping into the
concrete. Fiberglass is often used because of its high corrosion resistance.
However, fiberglass is expensive and difficult to connect to because of
its formed design. Plastic is used for thermal energy storage applications
with low temperatures and smaller volumes and can be an economical
choice [18].
Material choice should be based on tank area. More specifically, a designer
must consider leak potential, conduction into soil, and accessibility to the
bottom of the tank. For the inside of the tank, additional leak protection, heat
loading, drains, and controls for high and low temperature conditions are
important factors. The tank exterior must be resistant to ultraviolet radiation
and temperature effects and should have insulating and waterproofing prop-
erties. Weight bearing strength of all areas of a tank should be considered
because the outermost bearings carry the load, fluid, insulation, saddles, and
fittings. These design criteria are detailed further in the next section cover-
ing stress.
Stress and Strain
Mechanical Stress
Plane stress must be accounted for in the design of a tank. The stress tangent
to the plane of a tank's walls is called hoop stress, commonly represented as
σ, and is a function of the pressure or
p
applied by the fluid, the radius or
r
of the tank, and the thickness or
t
of the wall material. In this case,
p
is the
gauge pressure of the fluid as compared to the pressure outside of the tanks.
Cylindrical hoop stress is characterized as
σ =
pr
t
(7.2)
Cylindrical longitudinal stress is characterized:
σ =
pr
t
(7.3)
2
