Page 416 - Compression Machinery for Oil and Gas

Midstream Chapter 9 395

compaction measures and lift heights (typically 4 –6 );
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presence of weak soils near the surface;
frost depth;
location/depths of water table and flood plains;
soil resistivity (ties to cathodic protection and grounding for those designs);
soil pH-corrosion;
soil density;
seismic zones and risks, presence of expansive soils.
Reciprocating and centrifugal compressors can be packaged or utilized on a
fabricated skid, block mounted on concrete, or set on pile foundation systems.
Large gas turbine or electrical motor-driven centrifugal compressor packages
machines are also sometimes set on “tabletop-style” foundations, which are
configured much like a rectangular top table except with multiple supporting
legs consisting of structural steel piles or drilled concrete caissons. This style
is popular for larger machines and allows the space underneath to be used
for long radius large diameter piping and auxiliary equipment.
Compressor package and associated machinery foundations are one of the
most critical aspects of compressor station facility engineering. It is important
that factors such as subsurface geotechnical analysis, reinforced concrete
design, steel pile and/or drilled concrete caisson design, and dynamics of foun-
dation systems undergo expert attention. Currently civil and structural engineer-
ing technology is available to fully investigate these key design criteria.
Because foundation design is a highly technical science, a competent founda-
tion and/or consulting expert engineering group should be consulted prior to
starting any major compressor station project. Important phenomena such as
resonant frequencies and dynamic instability of machinery foundations as well
as complex three-dimensional (3D) dynamic engineering models should be
scoped and fully reviewed.
To correctly design a foundation for a large compressor unit, certain critical
information needs to be obtained from the manufacturer and other stakeholders.
The following minimum data should be available to the foundation designer:
1. Total weight of the package.
2. Base dimensions of the package.
3. Operating speed of the package.
4. Geometry and weight of the reciprocating parts including crankshaft, piston,
crosshead, connecting rods, etc.
5. Distance required to remove the engine and compressor pistons and
connecting rods.
6. Weight of the unbalanced rotating parts.
7. Geotechnical report.
Reciprocating gas compressor package bases (structural steel skids) are
designed to have sufficient mass and rigidity to support the entire fabricated
and assembled compressor package. Bases or foundations can be designed as