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Reciprocating Compressor - Full Bed Grout or Chocks

Reciprocating Compressor - Full Bed Grout or Chocks

Reciprocating Compressor - Full Bed Grout or Chocks

It has been about 25 years since I was heavily involved in grouting in a reciprocating compressor. At that time, our point of view was that full-bed grout was the best option for good reliability and long life. I seem to recall that we considered using epoxy chocks but decided against it. I don’t recall why. We are just getting ready to remove and regrout one of our compressors and had a foundation and grout contractor suggest that we should consider chocks. We contacted a recip compressor expert at one of our other plants and they agreed. I am looking for suggestions regarding the pros and cons of using steel or epoxy chocks rather than full-bed grout for a reciprocating gas compressor. Here are the particulars on the compressor:

Dresser Rand Model: XHH-VL-2 (two cylinders, two stages)
Driver: 3,500 HP synchronous motor
Service: 1200# make-up hydrogen for refinery hydrotreaters

The frame needs to be removed and regrouted because the frame extensions have broken free from the grout cap and are moving. This has resulted in movement between the frame extensions and the cylinders. We also have a lot of cracks with oil seeping out of them. I have included a picture to show some of the condition issues. It was probably a bad grout job originally with the frame extension using a separate grout pour from the rest of the frame. The frames were originally installed in 1993 with full bed epoxy grout during the original construction of the process unit.

Thanks for any feedback you can provide.

Johnny Pellin

RE: Reciprocating Compressor - Full Bed Grout or Chocks

i did several integral units (GMVs, TLAs, etc) w/ similar foundation problems and used concrete from mat to w/in 3-inches of unit footings. a 1-inch epoxy cap covered the top of concrete w/ embedded oil drip pan sloping to one end. the final 2-inches were epoxy chocks after the engine/compressor unit was aligned. never had a problem since. the epoxy does not allow the oil to infiltrate the concrete and cause cracking. for anchor bolts, a 2-piece anchor bolt w/ load monitoring studs were used. supernuts were used to provide the proper loads in anchor bolts. back then, carters-waters epoxy was used.
btw, the integral unit remained in place during the re-grout by removing concrete, installing Sch80 4-inch pipe w/ jack screws to maintain elevation of unit. this process continued until all concrete was removed. new rebar was tied into the mat.
i may still have a work scope if interested.

RE: Reciprocating Compressor - Full Bed Grout or Chocks


Thanks for the reply. We have no choice but to remove our compressor frame. The movement has been occurring for so long that we have started seeing movement at the spreader bar across the top of the frame. We have a recurring oil leak between the frame extension and the cylinder. We may have extensive repairs needed to the frame which could include line-boring. The compressor manufacturer has confirmed that our frame is suitable for the use of chocks, but they recommend full-bed grout as their standard. I would like to upgrade to load monitoring studs, but we do not plan to replace the anchor bolts.

Don't bother trying to find the scope from your job. Thanks again for the quick reply and the excellent example. That is one more data point suggesting that chocks may be our best option.

Johnny Pellin

RE: Reciprocating Compressor - Full Bed Grout or Chocks

a lot of work moving that much metal and good luck with that work. i was a skeptic at first about leaving the frame in place, but the contractor insisted they could do the work safely.
in-line boring, yeah, there was an ingersoll SVG (?) unit (1000-hp) that had the same and the unit ended up with custom bearings.
ask the compressor mfg: if the oil leaks continue, how long will the grout last? i doubt the compressor mfg makes grout material. yes, there are units w/ full bed grout and likely not having any problems.
load monitoring bolts are not that expensive and worth the expense.
about steel chocks, i seem to recall that a thermal barrier be installed between the frame and epoxy or grout to minimize heat transfer (thermal movement).

good luck!

RE: Reciprocating Compressor - Full Bed Grout or Chocks

Thanks again. I regrouted an old SVG twice in about 1992. My boss at the time insisted we did not need to wait 30 days for the green concrete to cure. It warped the frame and wrecked the main bearings. Our SVG was a V-12 engine with four compressor cylinders down one side. Not sure of the horsepower, but it was a monster.

Johnny Pellin

RE: Reciprocating Compressor - Full Bed Grout or Chocks

We probably could do the frame work in place. But, potentially reworking the fit for one spreader bar and one bearing cap, milling the face of the frame extension and line boring would take too long while chipping the block and doing a full regrout. We have a contractor who insists they can pick that frame out and put it on a truck in short order.

Johnny Pellin

RE: Reciprocating Compressor - Full Bed Grout or Chocks

What results can be expected from an old SVG?

RE: Reciprocating Compressor - Full Bed Grout or Chocks

results to be as good as originally designed.
every SVG component is replaceable, though original OEM replacement parts may be hard to find. a properly aligned unit w/ a good foundation, clean air, clean fuel, a decent ignition system, and a good lubrication system will provide years of service. there are many +50 year old old Clarks, Worthingtons, and Cooper-Bessemer units still in operation.

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