The compressor skid — the structural steel frame on which the compressor, driver, and auxiliary equipment are mounted — is often treated as a commodity item in package specifications. In reality, skid design has a direct effect on package vibration levels and is one of the areas where Tech Transfer made its most significant early contributions to the industry.
The Original Problem
When high-speed separable reciprocating compressors became common in the 1970s and 1980s, they were routinely mounted on lightweight fabricated steel skids. The new compressor designs had higher mechanical and gas forces than the slow-speed integral compressors they replaced, but the skid designs did not change to reflect this.
The result was widespread vibration problems. Skids that appeared structurally adequate — with sufficient static strength — had natural frequencies that coincided with compressor excitation frequencies, producing resonance amplification that caused fatigue failures in piping, instrument connections, and structural welds.
The TTI Contribution
Tech Transfer was among the first firms to systematically investigate this problem and develop heavier skid designs that addressed the root cause. The key insight was that the relevant structural property for vibration control is dynamic stiffness — not static strength. A heavier, stiffer skid with higher natural frequencies avoids resonance with compressor excitation; a lighter skid may be statically adequate but dynamically inadequate.
The practice of filling skid areas under the compressor and driver with rebar-reinforced concrete, which Tech Transfer helped pioneer, substantially increases the dynamic stiffness of the skid without excessive weight penalty. This approach has become an industry standard.
What a Proper Skid Analysis Covers
A complete skid dynamic analysis uses finite element methods to calculate the natural frequencies and mode shapes of the skid structure. The analysis evaluates wind and seismic loads, transportation and lifting loads, and operating dynamic loads from the compressor. The goal is to confirm that no natural frequency falls within the compressor excitation range and that vibration amplitudes and stresses are within acceptable limits.
