2
base times the height (š R H. For example, to compute
Material Estimates
the weight of the 2 1/2-inch extra strong steel pipe
shown in figure 2-3, you would use the following
The material you will use on a given job will be
procedure:
determined from specifications or plans. If the material
is not specified, you will decide what you need and
Step 1. Compute the volume of metal contained in
select it. Your decision will be based on the purpose of
2
cylinder 1, using the formula volume = šR H.
the structure or object, and the conditions that it will
Substituting known values we find that:
meet in service. Some of the "in-service conditions" are
resistance to corrosion, resistance to acids, or resistance
š = 3.1416
to wear. You will have to consider the weight to be
supported, pressures to be withstood, and working
stresses that may be encountered. Safety, too, is an
R = 1.4375
important point to consider in determining the material
H = 30 ft (360 inches)
to use on a particular job. There is no set rule to fol-
low. Each problem must be considered individually.
V = 3.1416 (1.4375)2360
ALLOWING FOR WASTE.--In most jobs, a
V = 2337.0 cu in.
careful study of the detail plans will reveal the exact
amount of material needed for a particular installation
Step 2. Compute the volume of metal contained in
or repair. However, it is sometimes impossible to use
cylinder 2:
every linear foot of a length of pipe or bar stock or to
use every square foot of plate or sheet metal. Some
š = 3.1416
waste is unavoidable, and an allowance for such waste
is necessary in material estimates.
R = 1.1615
WEIGHT CONSIDERATIONS.--Weight consid-
erations are important in shipboard repairs and alter-
H = 30 ft (360 inches)
ations. Consequently, it not only may be necessary for
V = 3.1416 (1.1615)2360
you to determine the amount of material required for a
job, but also to calculate the weight of the material
going into the job. The weight of pipes, tubes, plates,
V = 1525.7 cu in.
sheets, and bars can be determined in either of two
ways: (1) by referring to tables in a handbook and
locating the weight per linear or square foot of the
particular material in question; and (2) by arithmetical
computation. For example, suppose you need to know
the weight of a 30-foot length of 2 1/2-inch extra strong
steel pipe. By referring to the appropriate table in a
piping handbook, we find that this pipe weighs
approximately 7.66 pounds per linear foot. Thus, a
30-foot length weighs 229.8 pounds.
But, suppose you do not have such tabulated
information available. In that case, it is necessary to
determine the volume of metal involved and multiply
that result by the weight of the metal per cubic inch. To
compute the volume of metal in a pipe or tube, think of
it as being two cylinders. The outside diameter being
cylinder 1 and the inside diameter being cylinder 2. The
result obtained by subtracting the volume of cylinder 2
from the volume of cylinder 1 will be the volume of
metal (in cubic inches) contained in the pipe or tube.
Figure 2-3.--Actual measurements of inside and outside
diameters of 2 1/2-inch extra strong steel pipe.
The volume of a cylinder is equal to the area of the
2-16