Page 265 - Estimators Piping Man Hour Manual

240 Section Eleven—TECHNICAL INFORMATION

HANGER LOAD CALCULATIONS

The thermal deflection of piping in modern high loads within the system the supporting forces required
pressure and high temperature power stations has made of the adjacent hangers will be correspondingly
it necessary to specify flexible supports, thereby large.
requiring the designer to give considerable thought to Figure 1 illustrates a pipe line drawn in isometric
the calculations of hanger loads for the steam pipe with all the necessary dimensions shown in the same
lines. Most manufacturers of power station equipment plane as the related section of pipe. This illustration is
place limitations on the allowable loads at terminal limited to as few pipe sections as possible but incorpo-
points. Boiler and turbine manufacturers are especially rates most of the problems commonly encountered in
concerned about the pipe weight on their equipment power station piping support. The type of support,
and sometimes specify that the reactions at pipe con- spring or rigid, is not covered here as this is a function
nections shall be zero. Piping engineers are interested of the piping system's thermal deflection and should be
in knowing the proper procedure to follow in calculating treated as a separate study.
the loads at various points of support on a pipe line and The first step in the solution of a problem of this kind
also to determine the position of support on a pipe line is to prepare a table of weights. Such a table, for the
where the pipe load at the anchor or terminal point is pipe line shown in Figure 1, is given on the following
limited. page.
Pipe lines should be supported so that the load on Calculation of loads is accomplished by taking
the terminal points is not greater than the allowable moments about an unknown value and solving for a
load throughout the full range of thermal expansion. second unknown value, or if all loads except one are
Therefore, it is desirable to know the supporting known, summation of the individual loads will produce
force at each pipe suspension point and to have the the unknown load. It is preferred in this explanation
total supporting forces equal to the calculated weight that the summation method be used as check method on
of the piping system. the accuracy of the computations made in the moment
With these conditions in mind, it is quite evident method.
that the pipe support engineer has need for a method of The calculation of loads for hangers of a piping
calculating the supports that will be clear, concise and system involves first dividing the system into conven-
easily understood. ient sections at the following points in the system and
In the example problems to follow it is assumed that the order of preference is as listed: (1) Hangers,
the hangers have been located. The approach and the (2) Bends (either vertical or horizontal), and (3)
assumptions made in solving a hanger load problem Risers.
could be numerous, depending on the designer. The The next step is to isolate each section for study
solution that follows is not intended as being the only beginning with the section of pipe supported fay
method but rather as a method of producing a good hangers H-l and H-2. The solution of each section
balanced system for the problem under consideration. should be prefaced by the drawing of a free body
Of the approaches that could be made in the solution of diagram. This will provide a clearer picture of the
any problem there will be one solution that produces the steps involved in the solution.
best balanced system. Individual loads will very likely
be different but the total of each combination of hanger
loads plus reactions obtained should be approximately
the same in every case. Section 1
A well balanced suspension system will result in
values for the loads on the hangers to be in close Draw a single line sketch, preferably to scale, as in
proximity to one another provided all pipe is of the Figure 2, and show all dimensions and weights. (The
same size or there are no highly concentrated loads weight should be shown at the center of gravity of each
located near a hanger; where there are concentrated piece of pipe, valve or fitting.)

Thme t>*tf* reproduced through the courtesy of Grinnell Co., Inc.