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Interface with Structural Engineers

Interface with Structural Engineers

Interface with Structural Engineers

(OP)
I am quite interested in the cross-over between pipe stress and structural engineering. For 'fun' I am modelling up a pipe rack in Staad with the intent of importing it into AutoPipe and seeing what happens.

What kind of interface do you have with the structural guys? Do you give them non-code combination loads at each support (G, T, P etc) or maximum loads or something else?

I've been reading some comments on Bentley's forums, most of which seem to be along the lines of too much effort, working stress to limit stress = too hard, etc.  

RE: Interface with Structural Engineers

Not much cross-over really, pipe installations are a space frame.  That's how this structural guy wound up doing pipelines for 30 years.  I started in "tubular space frames" and "The pipes just kept getting longer and longer."

The practicle method is that the structural guys take 10% of the pipe wet load (assumed at 40 psf rack plannar area on each pipe level) in the horizontal direction.  Pipes on a rack, with expansion loops every so often, expand in both directions, theoretically, thereby limiting and/or cancelling out 90% of all thermal loads on the average given "bent".  Large point loads (those that wouldn't be caught with the above asumptions) from anchors, guides and stops are handled separately on a case by case basis.  

The Bently guys would have us do a complete begin-to-end stress analysis for totally restrained, underground pipelines ... if we listened to everything they said.

What would you be doing, if you knew that you could not fail?

RE: Interface with Structural Engineers

I haven't seen it done well.  I've seen places where loads were assumed to be a factor of the dead weight and then the exceptions were forgotton about until it was "Oh crap!" time.  I've also seen every last stinking support location was identified and a full load report with every conceivable load combination sent to structural.  Structural of course had no idea what GP1T1W1U2{3} meant and churned needless through all the data.

In all these cases, pipe stress was unable, unwilling, or unavailable to educate the structurals as to what pipe stress does, and vice versa for structurals educating piping.  On one project it a structural had no concept that steel expanded with temperature and the pipe stress guy insisted there were no thrust loads transmitted to steel because there were no untied expansion joints.

My suggestion to all that will listen:
1) use the data in the software programs to its fullest.  Don't deliver 1000 page hardcopy reports, they will assume you're a nincompoop who can only manipulate the computer.  Export data, sort it, filter it, pivot it, report only what you need to.
2) cross train a select group from these two disciplines, but don't make the pipe stress engineer tag an albatross in your organizatoin.

- 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.

RE: Interface with Structural Engineers

It has my experience that pipe rack design and pipe loading development is a "big deal" and can delay installation.

It is also an area that project management typically wants to gloss over and pay no atention to and unfortunately develops into a "learning experience" for the piping group.

Real companies, (Bechtel, Fluor, Shaw) have long established structural guidelines about this particular subject, and, knowing the importance of piperack design to project success, ensure that this matter is addressed.

Wannabees will flounder and lose money....
 

   

RE: Interface with Structural Engineers

I started using my method up there both at Fluor and Brown & Root.  All pipe stress engineers back then were structurals.  Although pipe whip restraints for So. Tx Nuc Plant were handled a bit more formally, that was not true for refineries.

What would you be doing, if you knew that you could not fail?

RE: Interface with Structural Engineers

(OP)
I went to a presentation a few weeks ago, "Seismic Design for Non-Structural Engineers". Just based on this, I'd say my workplace falls more into the 'wannabees' category. Pipe stress isn't important anyway really is it....

In previous designs I have seen here, thermal movements are ignored in the structural engineers analysis, with hydrostatic test loads used as the 'worst case'. (Well wind loads on the pipe are usually the worst case, but that's a little different).

Would a Google search return any results for a structural guideline from one of those real companies? I guess I'll find out now...

RE: Interface with Structural Engineers

The piping engineers also have to consider the structures moving due to wind/earthquake/wave motion/vibration (screenings)
/temprature etc and impacting on the piping. This is particularly a problem with GRP piping that has a very low strain tolerance such as in desalination plants. They are invariably built on the coast and exposed to high wind loads.  

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

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