should be as large as possible to prevent weakening of

the pipe and restriction of fluid flow. Six times the pipe's

diameter is a good rule, but there will be times when a

smaller radius is required. Too small a radius will flatten

the heel and wrinkle the throat of the pipe at the bend.

determine the total developed length (TDL) of a section

of piping with a 90-degree bend in three easy steps.

ing excercise are taken from figure 16-3.

1. Subtract the bend radius from the straight

section of pipe. Using the dimensions in figure 16-3,

subtract 18 inches (bend radius) from 48 inches (straight

section of pipe), which leaves 30 inches, the distance

from points A to C. To get the distance from B to D,

subtract 18 inches from 72 inches, which leaves 54

inches.

Serious injury to personnel

2. To figure out the total length of pipe for the bent

90-degree section of pipe, simply multiply the bend

Loss of a vital system that has no standby system

radius by a constant of 1.57. In this case, our bend radius

Where threaded fittings are not authorized, you will

of 18 inches multiplied by 1.57 gives us a total length

use a socket fitting. As in threaded pipe, you must add

of 28.26 inches for dimension AB in figure 16-3.

allowances to the "as taken" measurement of socket

3. To get the TDL, the final step is to add the length

fittings before cutting a length of pipe. The allowances

of the legs to the length of the bent section (30" + 54"

vary from brazed and welded socket fittings. In brazed

+ 28.26" = 112.26"). At this point, you may convert the

fittings, you must add the depth of the socket to the

decimal measurement into a fraction for easier use in

length of pipe before cutting. In welded fittings, there

measuring a section of pipe.

are several special allowances to take into consideration

when measuring your pipe. All welded piping systems,

regardless of material or service, require the use of a

small end gap clearance of l/l6 to l/8 inch between the

than 90 degrees, a slightly different process is used. This

pipe end and the fitting. This end gap clearance allows

for thermal expansion of the pipe end in the socket. You

must also take into consideration the reduced socket

depth if you are reusing a welded socket fitting. When

you remove the pipe from the fitting, you must remove

part of the fitting to eliminate the fusion area of the weld,

thereby reducing the socket depth. Refer to

MIL-STD-22 for exact fit-up of welded joint designs.

As you can see, allowances and measurements for

socket fittings are more exact than those for threaded

fittings.

The amount of pipe needed for a bend in a piping

system must be computed during the layout stage. If the

system permits bends to be used instead of elbows,

make the necessary allowance for the extra pipe

required to make the bend before you cut the pipe to

size. The first step is to determine the bend radius, which

16-3