Page 114 - Reciprocating Compressors Operation Maintenance

Design and Materials for Reciprocating Compressor Components 1 01

compressor cylinder

Composite

FIGURE 2-57. Pressure wave generated by double-acting cylinder.

When the physical length of a pipe or piping element is the same as
the acoustic length, a condition of resonance or pressure building-up
exists for a given exciting frequency.
A pipe that is in resonance has a pulsation or pressure buildup that can
be several times the pulsation generated by the compressor. This pressure
buildup can be substantial and can force the piping into vibration.
If the mechanical natural frequency of a pipe length should correspond
to the exciting frequency of this pressure buildup, the vibration could be
violent. The mechanical natural frequency is a function of pipe length,
cross sectional dimensions, and material.
To control the vibration then, it is necessary to detune the system by
reducing the pulsation, changing the acoustic response of the piping sys-
tem and/or reducing or increasing the mechanical natural frequency of
the pipe by a change in stiffeners or weight.

PIPE VIBRATION

Compressor piping vibration is generally due to pulsation. Vibration
originating from unbalance can cause vibration of piping in close prox-
imity to the compressor, but this is not usually the case. Vibration radiat-