Pipe Racks/Pipe Supports 3

[texeng88]

I work in the energy and chemicals industry and have been thrown into the position of a lead engineer on a few small projects due to my office being understaffed. I am still trying to learn the typical workflow of these types of projects and was hoping someone has some experience with pipe racks and supports. The way I have been working so far is for have the piping designer to put some temporary steel supports in his 3d model where he will need them, and then I will get into his model and look at his support layout at elevations and actually design the supports. Is this the standard workflow that projects typically follow?

 

[texeng88]

I should add that I am pretty fresh out of school with just a little over a year of experience.

 

[BAretired]

With pipe racks, you overdesign them. The cost of material is peanuts compared to the cost of beefing it up a year later when someone decides to increase the number or weight of pipes.

BA

 

[texeng88]

I agree. I typically use the PIP standard 40 psf on the entire piping level and add point loads for any lines 12" and above. I guess my question is more about the workflow on a project. I keep getting heat from my project manager that I am falling behind on the schedule on my pipe supports and equipment foundations, and when I try to explain that piping designer is still routing the pipe and working on the equipment layout he doesn't seem to get it...so I am wondering if I am somehow I am not understanding the workflow?

 

[delagina]

it depends on the company. some companies engineer do both the 3d modelling using frameworks and staad, designers only do 2d drawings. some companies, designers do the 3d modelling in frameworks.

regardless, you should be in close contact with your designer, and also with piping and equipment department.

 

[delagina]

btw 1 year experience and acting as lead engineer lol.

leave that company and work for "real" EPC companies like fluor, bechtel, jacobs, etc..you wont have the problem you are facing now.

 

[BigInch]

OMG. Don't wait for that. Pipe rack routings and elevations are decided in advance and the piper works to lay the pipe in the route. That works well except for a few assorted T supports that you can stick in place at the last minute and finish it off.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[TLHS]

Eh, on fast track projects I've designed lots of pipe racks in advance of piping information. It's important to lay out an upper bound for size of pipe and whether there are guides or other actual restraints on the rack. Once that's done, you can go through and approximate loading based on really worst case assumptions. Heck, I've designed racks based on future expectations that won't be fully designed for years

The problem is that working without fully defined scopes isn't something you want to be doing without someone with experience to help you. You'll end up in a situation where you don't know that something is critical or you don't know what to assume and get locked into things that won't work. You also don't just want to rely on the loadings the pipers have given you, because they don't necessarily understand the structure or what the governing factors may be. If you're not experienced enough to know what is reasonable, you won't know what you need to ask or push back on.

If you're talking 12 or 14 inch pipe and below, you can mostly live on assumptions with very little information. When you start going much above that, you need a better understanding of what things should look like if you're going to try and advance the work.

With regards to work flow, there's not necessarily anything wrong with what you're doing, but there's a suprising amount you can advance. From my experiences, a typical workflow in a normal pipe support project with no weird schedule requirements would usually be something like the following if you've got three major project phases:

Scoping:
-You are given a general idea of where the pipes are going and what sizes they are. From this and your existing knowledge you will come up with some basic framing, a layout, and a rough lateral restraint system. You'll often need some rough sizes for estimating, so you'd use previous experience of very quick math.

Basic Engineering:
- You'll start this generally with a rough piping plan that was developed during the last step. From it, you'll either have to do your own takeoff of piping weights and loads or possibly piping can give you something preliminary. Depending on the company you may or may not have a preliminary stress analysis of major lines at this point.
- Actually check and design your major members leaving a healthy margin on them. The harder something is to add capacity to, the more leeway you want to give. This is a judgement call depending on the specific situation. For example, if it's somewhere they might try adding additional levels to in the future you might try to get that written into the scope and significantly overdesign the columns and foundations. If you just suspect they'll add more pipes without checking anything you might go ahead and leave an extra 25 or 30 percent capacity in there.
-Think about worst cases. If it's an air line, check for hydrotest loads. If it's a line with solids in it, check what happens if a plug forms and it fills with solids. Check for lateral loads based on friction.
-You'll likely start your main drawings here

Detailed design
- At some point in this stage you'll likely get a stress analysis. It may not be at the beginning. Push to get something preliminary earlier.
- Incorporate the stress analysis into your design assumptions. Remember that the stress analysis is just one piece of information. It's not necessarily the governing item, there are reasons you would design to higher or lower values. It's just part of the puzzle. Make sure you understand what their analysis is actually telling you and incorporate it into the other situations you have thought about.
- Go through your structure, make sure you've thought about consistency, fit up, connections, welds, details, deflections, thermal effects, etc
- Finalize your drawings with all of the above information
- Somewhere in here, your engineering and drawings should be checked by someone
- Likely near the end, you should verify that a finalized stress analysis matches up with what you've used for design or at least falls within the extra meat you've left in the system (remember, this final stress analysis is *still* just one piece of your design basis)

 

[TLHS]

Also, if you're still getting a feel for industrial structures, I would suggest picking up the book "Construction Management and Design of Industrial Concrete and Steel Structures," by Mohamed A. El-Reedy.

It's not comprehensive on anything, but it's got a breadth of coverage that touches on most major types of industrial structures and at least gives you a thought on how to approach them and what you should be considering. There are also references after each chapter that can point you towards more information. It generally tells you where all the factors and numbers it's using came from, which is unusual and helpful.

 

[Gumpmaster]

On the big piping projects I've worked on, I think it's best to throw something in the model for the piping folks to place their pipes on.

Many of the piping designers will just place their pipes from points A to B without much thought for how they'll be supported. I've seen 1" lines 40ft off the ground without any other pipes or structure nearby.

Place some racks and frames in the model (At general locations agreed to by the lead piping person) and ask the piping folks to place their pipes in, on, around those. Watch out for piping designers placing their pipes 2" apart without thought to how to fit the pipe straps on. Request a minimum spacing between pipes (especially larger pipes).

Check the mechanical model on a regular basis so you can catch problems as they progress.

There is a good AISC paper (2 or 3 years old maybe) on pipe rack design that layes out a bunch of generalities on the loading and design.

 

[TLHS]

Yeah, I recall a good article in the journal a couple of years back. I have a hard copy somewhere that I'll try to dig out if I remember. It *may* be "Design of Structural Steel Pipe Racks" by Drake, but I'm not completely sure. If it is, you can buy old journal articles from the AISC for $10 online, generally. They're free if you or your company has a membership.

There's also a good three part article I've got from the March 1979 'Hydrocarbon Processing' by Dr. Channagiri V. Char that gives you good places to start when you're designing with limited information. I have absolutely no idea where I picked this article up. I'm not around for the next few days but I might remember to scan it in next week.

 

[texeng88]

Thanks for the responses, I will definitely check out those publications you mentioned. I work for a large fortune 500 engineering firm so we have a large database of all of the AISC articles, I will take a look at the one you mentioned.

 

[jnich]

Yep, you need to pass the heat to your pipers and mechanical engineers to lay out the pipe and establish their elevations. My experience in pipeline facilities has been that establishing the suction hydraulics to pumps is the first step in the design. Once the piping is laid out to satisfy that (in x-, y-, and z-directions), then you can design & model your supports & foundations. The biggest snag in my experience is coordinating the two disciplines to avoid interference and constructability issues. Good luck.