Welded Pipe on Production Skid

[curvyrace]

My company has built custom fluid conditioning skids for many years using welded pipe. Now we want to create a few standard production units with welded pipe and fittings. I was wondering how other companies deal with the tolerance stackups inherent in these kinds of assemblies and the fact that welded pipe is unforgiving? Should we just count on fitting the piping to each unit on the production line and, if so, what is the best method to minimize the fit-up required? Thanks!

 

[ColonelSanders83]

Generally we plan out the runs and prefabricate as much as possible, Then we do a dry run with all the equipment set on the skid and perform field welds in as few as possible planned locations. The key is to plan out where you need a field weld to account for tolerances. Sometimes we can get away with only one field weld, other time three are needed.

PS Field weld should translate to in situe weld as all the welding is done in the shop. The only difference is that the spools are normally built on tables with rotational positioners so welds are made in the vertical direction only. Whereas the field weld requires a welder who can do all directions.

 

[racookpe1978]

I understand you are building the skid in the shop, then installing the whole skid as an assembly in the field, in the client's plant.

Your pre-fabricated "inside the skid" pipes should be darn near perfect: Certainly your jigs for each pipe spool need to be built to +/- 1/8 or less. 1/16 tolerance for the jigs should be easily fab'ed. Same for your skid pipe supports, steel, pump foundations, etc.

Then you build all of your pre-fab'ed spools in those "good" jigs, and only allow errors to creep in the field where the skid will be installed. "Expected" changes (places where you leave margins for field cuts and welds), if needed at all, should be limited to the connecting flanges coming out of the skid.

There? You can't tell: field pipes may be even several feet off location.

 

[curvyrace]

Thanks guys! I appreciate the help. racookpe1978 you're dead on with how we build our skids, but up until now we haven't used welding jigs since everything was custom. On these production skids, I think we'll have to start using jigs where it makes sense to.
Colonel, I've started to try to plan out how we can prefab as much as possible, then make adjustments in only 1 or 2 places. Thanks Again!