Field Booster Unit Installation

[DLite30]

I'm looking for someone who has any experience with installing small (1000 hp or less) skid-mounted reciprocating field booster compressors (nat gas service)?

My experience is mainly in large concrete-slab mounted units inside compressor buildings, and I have no practical experience in these cheap, in-the-dirt installations.

I'm probably making a mountain out of a mole-hill, but it's a hole lot more expensive to estimate a mole-hill and end up having to go back and build a mountain.

Some of my main concerns are:
-Settling of the any type of dirt bed (compacted or not)
-Piping strain due to movement due to settling or the skid "walking" around.

I'm specifically interested in what preferred method you may have in setting the unit. Examples:

-Concrete slab & anchor bolts
-Compacted dirt bed(such as caliche), and what materials are preferred for this type of bed.

Any ideas you may have and are willing to share would be appreciated.

Don't post if you have speculative ideas...looking for guys with real experience.

 

[bcs5274]

this is what i do and how we do installs in this area of the usa, if it is going to be in north central usa i would be happy to help

 

[bcs5274]

forgot to add that, all new installs that i speak of around here are concrete filled skid put on a compacted gravel pad, ease of install and of decommissioning of the location when field is depleted

 

[DLite30]

I appreciate the offer!

The units we're working on now will be in south and east texas.

I can confirm that the skids will be concrete filled.

So you do not usually install any kind of structure (concete anchor or sleeper) to keep the unit from moving back and forth or twisting?

Another question regarding rainwater: How do you deal with the rain water that collects on skid? Do you use a below ground sump and then pump it to a storage tank, or what other kind of method do use to remove the rainwater...we can't allow it to overflow onto the ground.

 

[zdas04]

Here in New Mexico, we have a large number of nominal 1,000 hp units that are set on concrete foundations and grouted in. We have a smaller number of units in that size with concrete filled skids dropped in the dirt. They work just fine. The "dirt" is pretty level and compacted with a wackypacker (pretty good, but still a "lawn mower" back and forth motion so missed areas are common).

Smaller than 1,000 hp there are very few foundation/grout jobs. There are hundreds of CAT 3412 (about 550 hp at this elevation) compressors dropped in the dirt. These also have concrete filled skids.

If you're looking to pay for an answer there are a lot of consultants out there.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"It is always a poor idea to ask your Bridge Club for medical advice or a collection of geek engineers for legal advice"

 

[DLite30]

Thanks for your input, David

However, most of the "consultants" I've worked with or run into are worth less than the Canadian change I have in my pocket.

 

[bcs5274]

average install is a 2 foot compacted "base" of "road base" material (sand and gravel mix) with moisture added to get max compaction, top of pad higher than ground level, most pipe the skid drains to a fiberglass tank under ground next to skid, vac truck pumps tank and hauls to evap pit, let me know if you need more, willing to help regardless of location

 

[dcasto]

ok, opinions, zdas?

I've set Cat 3606 (1700HP units on packed caliche. Normally thats just above the size normally set on "gravel". Cat 3516's and Wauk7042's are on gravel. A044 or cat 3520 or cat 3606's are a toss up. By the cat 3608 yeah, they are set on concrete, but no grouting in. A cat 3616, its grouting in time.


NOW a new revelation.... Screw piles, look them up. We aree seeing them used inlieu of concrete pads....

 

[zdas04]

Setting a 3606 on gravel only works if you spent your engineering money on the skid. It has to be seriously stiff and seriously strong. Even at that, it probably ends up less expensive.

I've used devices that look like the screws you use to shore up a sagging foundation with really good success. Is that what you mean? Again, it takes a well engineered skid, but seems to work really well.

At the other end of the spectrum, we had a site that was built on fill and the first three compressors installed were shaking themselves to death. I spent some time with a Geotech Engineer and he recommended that we excavate down to bedrock (the hole was 20 ft wide, 19 ft deep at the deep end and 9 ft deep at the shallow end) then fill it with "flowable fill". We set a matrix of rebar a couple of feet into the fill, then poured a conventional foundation and grouted the compressor in. The 7042 driving a HOSS compressor never shook at all. Nearly a perfect result.

Bottom line of the story is that a thousand hp is a reasonably big load, and the mass of the cylinders create some interesting moments and couples. Engineering is required (either in the skid and/or in the foundation) to create a way to manage those forces. I wouldn't have a problem setting a Cat3606 or a Waukesha 7044 on a gravel pad if the skid was designed for that service.

Now when we design a skid to be grouted and throw it in the dirt, things don't end well.

If the installation calls for a compacted 2 ft of road base, I'm pouring a foundation. It takes forever to compact a 2 ft thick pad in 6-inch lifts, and it isn't worth it. You can set a portapad cheeper.

David

 

[dcasto]

I just came from a site where the geotech crew hit coal (unminable because it was like 50% bauxite?? or thats what they claim) They had to cut out an 8 foot deep seam. Below it was bed rock and they set 5 3516 packages on 1 1/2" rock inside a stem wall with a building and 3 ton crane.

 

[DLite30]

I've read up on the screw piles that dcasto was talking about. In soils were driven or drilled piers may be required they may be a economical substitute, or maybe to replace a large number of pipe supports, or cable tray foundations.

Soil analysis is another thing. This one is such a rush job, that we can't get a soil guy out there in time to drill, analyze, and report back, before the unit is expected to be inservice, and the PM didn't do any of this ahead of time.

The skid is a vendor's standard, wide-skid, full runner, tall beam, concrete-filled, in the dirt design.

Hopefully, we'll get lucky and everything will be okay...and the PM will go off all proud and all.

 

[bcs5274]

there is skidded and housed packages all over canada set on gravel pads including cat 3616's , it can be done if done properly, also we have units set on piling and then filled in around the piles with gravel, depending on location and company preference