Page 364 - Improving Machinery Reliability

330 Improving Machinery Reliability

Figure 7-2. Resultant forces and moments at the pump centerline.

These loads, either from expansion of a pipe or from other sources, can cause shaft
misalignment and shell deformation, thus interfering with internal moving parts.
Therefore, it is important to design the piping system to impose as little stress as pos-
sible on the equipment and, ideally, it is prefened to have virtually no piping stress
imposed on the equipment. The established practice is for an equipment manufactur-
er to specify a reasonable allowable piping load and for the piping designer to design
the piping system to suit the allowables. The allowable piping loads are generally
determined solely by the equipment manufacturers without any participation from
the piping engineering community. The values so determined are usually too low to
be practical.
Machines designed with unusually low allowable pipe load are almost certain to
be weak machines. Weak machines also complicate the layout of the piping system
in meeting allowable values. Unusual configurations and restraining systems are
often used to make the calculated piping load stay within the given allowable range.
However, all these efforts are very often just exercises in computer technology. The
main reliability problem has not been solved. A better, sturdier equipment design
with some common sense piping arrangement is the basis for improving reliability.