Page 415 - Compression Machinery for Oil and Gas

394 SECTION III Applications

equipment to keep the piping off the ground, prevent excessive sagging and the
stress, react to static and dynamic loads, and transmit these loads to the ground.
The installation of support types such as simple weight supports, guides,
stops, hold-down clamp, springs or anchors at certain specific locations is typ-
ically needed to guide or force the thermal expansion of the piping away from
load sensitive equipment. In most natural gas transmission compressor stations,
the primary restraint type should be a strap type hold-down clamp for vibration
control.
For any new piping system to be installed, a thermal piping stress analysis
should be performed as required by the ASME B31.8 code. Due the compres-
sion process, the discharge gas will increase in both pressure and temperature,
which results in thermal expansion of the piping. The amount of thermal expan-
sion can vary from a few thousandths of an inch to over an inch. This thermal
expansion, along with the pressure and weight loads, will result in static pipe
stress, equipment and vessel nozzle loads, restraint loads, etc. A computer-
based analysis is typically performed to calculate and confirm acceptability
of these loads and stresses. Design modifications (such as in the installation
of thermal expansion loops, offsets or modified restraint types and locations)
may be necessary to concurrently satisfy all necessary design considerations.
Requirements for vibration control should also be carefully considered, and
balanced with the need for thermal expansion, as these two requirements often
have conflicts. See Chapter 11 for additional discussion on vibration control.

Filters and Separators
To remove liquids from the gas stream, it is usually necessary to install one or
more large filter separators or scrubbers at the inlet of the station or near any
critical equipment, such as compressors. If not removed, these liquids can cause
catastrophic damage to compression machinery.

Foot Print Size/Weight/Unbalanced Forces/Foundations
One key to rotating and reciprocating machinery reliability is the foundation
system. One of the main functions of foundations is to support the machines
at a precise elevation thus allowing the original precision alignment to be main-
tained over the life of the machine. Besides the critical task of maintaining the
alignment of the machine, the foundation must apply enough mass to withstand
the unbalanced forces that the operating machine produces. Good engineering
input from the manufacturer of the machine is essential to the designer of the
foundation, but equally important is a geotechnical analysis of the soil and the
conditions in which the soil and foundations will exist.
Important parameters to be addressed in a good geotechnical report include:
soil properties and types;
maximum soils bearing loads;
cut-and-fill slope ratios;