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FOUNDATION REPAIR COMPRESSOR & MOTOR REGROUT
Project: J-602-A gas compressor foundation repair, compressor regrout, and electric motor grout baseplate regrout.
1. ORIGINAL CONDITIONS
The machine in question is a Worthington Type BDC 1-1, gas compressor in Process Unit 6, powered by a direct coupled Siemens electric motor of 410 kW at 422 rpm.
An inspection of the compressor was carried out on 14 June 2007 by Alphatec and customer engineers, to evaluate the existing problems, and discuss outline repair methods.
The compressor was manufactured and installed in 1967, and was grouted in place with a cementitious grout material. The machine had been shut down because of high vibrations, so it was not possible to see how the degree of movement of the crankcase within the grout. The grout was seen to be thoroughly oilsoaked,and several cracks and separations were visible. The grout must be replaced by a modern epoxybased grout product, correctly mixed and installed by a competent and experienced contractor.
The motor baseplates were very poorly supported by the surrounding grout, with evidence of voids over large areas. The possibility of corrosion of the baseplate was also considered, which can often be caused by induced currents within the concrete and the cement-based grout material. For these reasons, a regrout using epoxy grout was recommended.
The secondary supports, under the intermediate bearing, the crossheads, and the cylinder heads, were all seen to be in bad condition due to oil contamination, and a regrout was recommended.
Many of the piping supports were also in bad condition, and a regrout of those closest to the compressor was recommended.
From the foundation drawings, it was calculated that the above-ground plinths had a combined volume of around 22m3, giving an estimated mass of 54 tonnes. Based on the foundation-mass-to-power rule of 100 kg/kW, this should be enough to damp out the vibrations. However, another rule suggests 6 times the weight of the compressor train, and it is unlikely that this requirement is met. Injection through the foundation and into the underlying mat was therefore recommended, with an exploratory core hole drilled before the main drilling to establish the depth of this mat.
There was some discussion about the connection between the compressor anchor bolts and the concrete foundation, and a secondary injection to deal with this problem was planned.