base times the height (š *R H. *For example, to compute

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

cylinder 1, using the formula volume = š*R 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

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

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.

The volume of a cylinder is equal to the area of the

2-16

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