Reciprocating Compressors – Foundation Design
Satisafactory compressor installations many times depend on how well the foundation or support structure was designed. An inadequate foundation design can result in equipment damage due to excessive vibration. The money saved by cutting corners on foundation design effort may be spent many times in costs associated with high maintenance and lost production.
Due to the basic design of the compressor, its rotating and reciprocating masses produce inertia forces and moments tha cannot be completely eliminated and must be absorbed by the foundation. The manufacturer has the ability to rninimize the magnitude of these forces and moments by adding counterweights to the crossheads but cannot totally eliminate them.
In addition to the unbalanced forces and moments, the foundation must absorb the moments produced by the gas torque. This is the torque created by the gas pressure forces as the compressor goes through a revolution. The compressor manufacturer must provide the magnitude of the resulting forces and moments and the gas torques.
Typically foundation design engineers have only used the compressor unbalanced forces and moments in their design calculations. Recent experience has found that the moments created by the gas torque can have a significant impact on foundation design. Detailed information and good design practices for compressor support structures and foundations may be found in Design of Structures and Foundations for Vibrating Machines by Suresh Arya, Michael O’Neill, and George Pincus.
For complex offshore structures or where foundations may be critical, finite-element analysis computer programs with dynamic simulation capability can be used to evaluate foundation natural frequency and the forced vibration response.