Stub Up Location Accuracy

[StevenHPerry]

For stub ups from underground piping, what accuracy (and/or precision) do you design for? What is actually achieved by construction?

Of course there's a story behind this. On a recent job, a nameless construction partner was off from a namless design firm's coordinates by more than a foot and of course only 3" of clearance was designed. I've witnessed essentially the same problem at multiple design firms and multiple constrution firms. It seems to be accepted as a fact of life. Anyone have a different experience?

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[11echo]

Relating to accuracy, I worked in the design/drafting dept of a major oil company some years ago, the projects dept kept coming to us about the "back charges" the construction companies were charging for "design discrepancies"! They wanted to know WHY we couldn't design projects "correctly"!?? ...We went out on the latest project where there were issues, the construction people had mis-locating a 1500 BBL tank by 20 ft., and were back charging the oil companies to "fix things"!

 

[pennpiper]

I suggest you consider looking at the Pipe Fabrication Institute Standard PFI ES3. This normally is applied to Shop Fabrication of pipe spools.
However, if you are dealing with an Pipe Installation Sub-Contractor and make PFI ES3 a part of the contract then you should be able to make them rip it out and make it right.

prognosis: Lead or Lag

 

[StevenHPerry]

Ripping it out has not yet been an option because of schedule impacts. Plus the construction partner is often on the same team and owns the rework to above grade connections anyway. It just bothers me that this defect is accepted and repeated.

The contractors' most recent claims have been that the backfill process routinely shifts whatever is in the trench. I can understand how that might happen, but are there no mitigating measures to be taken?

Perhaps shooting the coordinates should be done after backfill but before the finished surface is put on?

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[hvacpiper]

Wow..3',if we're off 2" with our stub ups,it usually requires a re-dig.(this is small bore sanitary piping into walls I'm refering to)I don't know if I'm comparing apples to apples,but we would never be allowed to get away with that much error.
In most of our "new build" jobs,we draw all piping 3D,export co-ordinates from our CAD drawings,to a trimble total station,and then layout our pipe hits with the total stations.Generally, we(the mechanical contractor),tell the steel erectors or carpenters when they're off...
Shifting pipe while back-filling sounds like BS to me..and I've laid quite a bit of pipe..

 

[STYMIEDPIPER]

It appears that the installation contractor had a bad measurement or the benchmark coordinates were incorrect. Usually my firm will add an additional 6 - 12 inch length to piping spools in the X & Y pipe runs for contractor to cut to suit the desired dimension/ location. On occasion, due to contractor oversight or accelerated pace to install the pipe the contractor fails to cut the additional length of pipe and thus erranous stub ups occur.If the severity of the installed location creates an adverse impact to the downstream pipe runs then you probably have little recourse but to require the installation contractor to resolve/ rework/ revise the stub up. Any piper with field experience will attest that things do go astray and field fixes are required at any large industrial construction site due to an abundance of possibilities. 3D models have helped to lessen the interferences but Mr Murphy (of Murphy's Law) still roams the job site.