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	A typical reciprocating compressor installation, including the top of the concrete block and the chock mounts.

A typical reciprocating compressor installation is shown to the right, including the top of the concrete block and the chock mounts. Engineers at Southwest Research Institute (SwRI) help increase foundation block integrity and foundation block life and reduce block maintenance costs by predicting both compressor foundation loads and the stresses they cause, and the potential for concrete cracking. Engineers then analyze alternative approaches to control stresses and cracking.

Load Prediction

Compressor loads are determined based on rotating inertias, reciprocating inertias, and compressor operating conditions. The resulting gas and inertia loads are applied to a model of the frame and block to determine the magnitude of compressor loads transmitted to the block. Features of the load prediction method include:

• Gas loads based on prediction of compressor cylinder pressure variation

• Cylinder valve resistance and stage flow matching for multi-stage units

• Throw-by-throw analysis of gas and inertia forces

• Finite element modeling of block and frame flexibility

• Addition of anchor bolt loads field and consultation services

Block Stress Prediction

A more detailed, nonlinear analysis of the concrete block determines the stresses and potential for cracking.  Adjusting parameters, such as anchor bolt length, concrete tensile strength, and the presence of post-tensioning bolts, reduces the potential for cracking. The analysis includes:

• Rebar

• Different concrete strengths in tension and compression

• Cracking

• Compressor loads

• Anchor bolt loads

• Any additional loads from post-tensioning bolts

Supplementary Services

A number of analytical and field problem-solving services are available at SwRI that supplement and complement foundation block stress analysis, including:

• Prediction of block thermal distortion and grout/concrete interface stresses under compressor heat loads

• Detailed analyses of stresses and deformation in alternative tie-down and chock designs (such as polymer vs. steel chocks and different grouting arrangements)

• Foundation dynamics including natural frequencies and forced response based on elastic half-space soil representation

• Shaker studies to measure dynamic response and resonances of the foundation

• Field monitoring of alignment changes using lasers or liquid level probes

• Field measurement and monitoring of compressor and foundation vibrations as a means of assessing installation integrity

• Strain gauging of piping to assess vibration severity and failure risk

• Compressor performance measurement and analysis

• General problem-solving services for compressor installations

For more information about rotating machinery technologies at SwRI or how you can contract with SwRI, please contact Klaus Brun, Ph.D., at kbrun@swri.org or call (210) 522-5449.

machinery.swri.org

| Fluids and Machinery Engineering Department | Mechanical Engineering Division | SwRI Home |

Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

January 03, 2013