Compressor Piping Alignment

[reza100]

We are purchasing a replacement compressor which is of a different design to the existing but vendor was asked to design the replacement compressor such that the nozzle locations will match the existing. This compressor is in cryogenic service and the alignment and nozzle loads are critical to the application.

For new compressors, there will be always field welds to ensure alignment of piping. But, what about the time we have existing piping and a new compressor? Does anyone have experience with this scenario? Should we plan for cutting and welding in the field? What precautions are you recommending to ensure piping alignment?

 

[rQuestionEngineering]

Nozzle must match.
It should be considered during design.

At this point, you have no choice but to modify the piping to match the new compressor.
You might also need piping to review the new modification.

 

[LittleInch]

The issue is which is easier to adjust?

Installing a large heavy piece of equipment to the nearest mm is really quite hard to adjust. Moving a piece of pipe to a fixed point is just must easier.

So long as there is some removable piece of pipe to allow installation of the pump without damaging the pipe work it might be possible, but will take longer.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JJPellin]

I have never done this with a centrifugal compressor. In my experience, compressors are rarely replaced entirely. This is much more common with pumps. I have installed "drop in" replacement pumps from a different manufacturer than the original. The new machines were designed based on the original outline drawing to mate up to our pipes and bolt down to our base. I have never had problems (than I can recall) with the make up of the piping. I have had interferences with the pedestals, base or other steel structure. Some of these elements are not called out in great detail on the outline drawing.

If the piping is well designed in terms of supports, it should not be a problem. If the piping is designed well from a standpoint of low pipe strain, it should have adequate flexibility in case the nozzles are off a small amount. I would probably take the chance on the piping working out rather than making up a bunch of new piping with leave-longs and field welds. But, I would be confident that my maintenance organization would be capable of making some rapid piping mods if needed. In other words, we have enough piping engineers, fitters and welders to cut and reweld the existing piping or even fab up new spools on short notice, if needed.

You are more likely to have piping mate up problems with the small bore support piping (seal oil, lube oil, buffer gas) than the main process lines. I have had that problem when swapping out a set of dry screw compressors. One connection was at a strange compound angle and the new one was not the same as the old one. But, this was a 1" pipe that we were able to easily modify on site with existing resources.

Johnny Pellin

 

[reza100]

@JJPellin, Thanks for the response.

Yes, the compressor replacement rarely happens, however this is one of those rare cases!

The lube oil piping will be completely replaced. The new compressor is coming with Dry gas seal so seal piping will be all new. My problem is only the process piping.

On the piping side, piping is as flexible as it could be. Lots of spring cans/hangers. However, as I said this compressor is in cryogenic service (-200°F) and nozzle loads are a problem. There is a limit on what you can do with piping flexibility analysis because the suction pipings have to be kept short. I'm concerned that even a small piping misalignment can cause trouble during installation and eager to know if anyone has done a similar project.

 

[JJPellin]

You said the compressor was a different design. Is it still the same manufacturer as the original compressor? If so, they should have dimensional drawings of the casing and patters that should allow them to match it more exactly. If the new compressor is from a different manufacturer without those detailed drawings the risk is greater. They would be basing their design on the general arrangement drawings. You could reduce your risk if you have someone come in and laser scan the installation to get more accurate locations for the piping. Based on your concerns, paying $10,000 or so for a laser scan might be money well spent.

Johnny Pellin

 

[reza100]

@JJPellin

The manufacturer of the old compressor has been bought by the new compressor vendor so they have the original drawings.

We have done a complete 3D laser scan of the area, but it's been taken during operation at cryogenic temperatures so the nozzle location will be somewhat different from installation temperature. The vendor can of course back calculate the location, however that's more to know if there is any significant misalignment. We need to comply to API 686 misalignment limits per vendor IOM.

 

[JJPellin]

Same manufacturer and a laser scan. Don't worry. It will fit just fine.

Johnny Pellin