Machine Foundations


In the typical installation of a block-mounted gas engine compressor, such as is found in gas transmission compressor stations, in gas processing plants.  First, it provides a means of distributing the combined weight of the concrete block and the machinery into the concrete mat and the soil below.  Secondly, through its mass, oftentimes three to eight times that of the machinery, it absorbs those dynamic forces which are a by-product of the work being performed by the machine.

The more evenly balanced and smooth running the machine, the less unbalanced forces there are which must be transmitted from the machine, through the grout and into the foundation.  An understanding of this function points out the importance of a good grout and anchor bolt system to join the machine to the concrete block.  Excessive vibration is often a symptom of a problem in one of the links in the attachment system.   It also can be from an abnormal machinery operating condition, where the unbalanced forces have increased beyond normal operating forces.

Reciprocating compressor crankshaft alignment determines machine life, downtime outage and costs, wear part usage, and when a regrout or foundation repair is necessary. When a foundation repair becomes necessary, it should be looked upon as a chance to upgrade the old foundation, address the cause of the problem, and prevent it from reoccurring. The foundation should be rebuilt and reinforced with rebar to today's design standards. The chocks should be upgraded to a new chocking system. The anchor bolts should be repaired or replaced with new high strength anchor bolts made per ASTM A-193 specifications. These upgrades can more adequately address typical alignment related foundation problems, such as cracking and foundation integrity and stability than a simple regrout.

A compressor foundation must be able to absorb and transmit the dynamic loads it receives into the mat and subsoil below. To do this it must be monolithic and properly reinforced with rebar. Reinforcement is most important in the upper block area. The best way to achieve this with the materials that are available today is with a concrete repair material reinforced with rebar.

Cracks in the foundation, particularly those found in the lower block, will not be corrected by just chipping out the old grout and repouring more new grout. Chances are the problem will reemerge over time and eventually will have to be corrected. Horizontal and vertical cracks in the foundation, especially those that are weeping oil or fluids must be addressed.

Cracks in the upper foundation block can be repaired by chipping out below the crack line for horizontal cracks or until the crack is gone for vertical cracks. A concrete repair material reinforced with rebar is used to rebuild the foundation. A 3 to 4 inch epoxy grout cap is poured on top as a precision, non-shrink, chemical resistant grout cap. A chock is installed at each anchor bolt to provide an adjustable support system.

Cracks in the lower foundation block become an economic and engineering problem. Economics usually do not permit a complete foundation removal and replacement. A simple regrout will not correct the problem. The solution is to rebuild and reinforce the upper 18 to 24 inches of the block area with a concrete material. The cracks in the lower block are bridged with post-tensioning bolts to bring the lower block area back into a more monolithic state. The highly reinforced upper repair area is post-tensioned to the lower block repair to tie the entire block back together. This provides an economic solution that is not as good as a new block but provides a better engineered, long-term repair than a simple regrout.

Machinery Grout is a material; either organic (such as an epoxy) or inorganic (in the case of cement-based materials) that serves as a filler between the bottom of the machine base and the top of the concrete foundation or metal equipment skid. Typical machinery grouts are flowable, virtually non-shrinking or slightly expanding, and serve to support the equipment base at a precise elevation within .001" over the life of the machine. Usually installed 1 " to 2" in thickness, they fill the gap between a non-precise top elevation of the concrete block and the machined bottom of the equipment base. Grouts only keep the machinery base from moving downward. An integral right angle drive gas compressor produces loads in the horizontal and vertical directions. Horizontal movement is restrained by the clamping action of the properly torqued anchor bolts against the machinery grout. You can see why a machinery grout has to be a tough material. It must be able to withstand prolonged com-pressive loads, at equipment-operating temperatures, without creeping or allowing the base to deflect, as this will disturb the alignment of the moving parts of the machine.

Grout has to be used in conjunction with a properly torqued anchor bolt system when both static and dynamic loading is involved, such as with compressors, turbines, pumps, gear boxes and most heavy industrial machines. It takes both good grout and good bolts to properly hold the modern machines industry uses today.




Case Studies
An Investigation of Reciprocating Compressor High Vibration Problem at PPMSB, Sungai Udang, Melaka, 2008 Read More>>>
An Investigation of Amine Circulation Pump (Motor Driven and Steam Turbine Driven) Problem at Gas Processing Plant B, Santong, Paka, Terengganu, 2005 Read More>>>


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