Who knows how to solve this piping problem with AutoCAD

How do I model (or calculate) the fewest welds/fittings required to change angle and elevation in a pipe run, as shown in Option1 below.

For this example the constants are: 8" standard steel pipe, one of the fittings is a standard butt weld 45 (12" radius), bend angle is 70 degrees, and the elevation change is 9". The custom fitting is cut from a standard 8" long radius 90.

Note: Option2 is just shown for reference, I'm only interested in solving Option1

BTW, the solution does not have to be modeled with 3D objects if anyone wants to use lines and arcs along the centerline, but tangency must be maintained for all segments/planes.

I do not know of any contractor that will put the torch to an elbow and field cut it to create a 70 degree fitting. I wonder how they'd even align it level on a pipe roller, haha... Okay kidding. In all the piping handbooks that are floating around, sure this is doable and it's documented. But Carbon Steel Schedule 40 & 80 fittings come in 90, 45, and 30. This is just standard piping layout and installation, of course.

But in my field experience, we would 90 up, then roll the top offset 90 to the 70 degree position. Obviously this doesn't hit the 9" elevation change, but in my experience, that would not be acceptable and you'd have to work within the dimensions of back-to-back 90s, which with 8" diameter pipe, 1.5 End to Center, that's 24" offset. So, is the 9" offset the only way? Or are you just testing some custom routing?

Attached is an example, which you probably already know I'm sure:

https://dl.dropboxusercontent.com/u/4989089/Images/cadtutor/2013-06-11/Pipe_Example.dwg

In process piping, small offsets and cut-back fittings are very common. Option2 is what's commonly used because it's easy. I refuse to put 3 fitting together like that because; 1) it's more welds and/or more cut fittings 2) it looks like garbage.

I was "hoping" AutoCAD MEP could do it automatically via routing preferences, but it appears not. Surely there's a math solution, but I've yet to find the person that knows it.

Hopefully, this won't detract from the original question, but there is a solution that doesn't require cut-back fittings. The 3rd scenario at the top right (below) uses two standard 45, but I still don't know how to calculate the length of pipe between the 45s so the total angle will be 70 with a rise of 9"

I guess we just see things differently. Like I previously stated, to me, it takes more labor to calculate, custom cut two fittings, then weld them together versus simply welding three fittings. You're taking two cuts and three connections of welds, versus zero cuts and four connection of welds. Plus, it opens more room for error. The last process piping job we did was for Whitewave Foods, which was a $15M mechanical contract. HUGE friggin' job, and we did it 100% BIM. There were about 30 different piping systems - carbon steel pipe, socket weld stainless, aluminum, copper, you name it and it was there (as far as piping goes). Never did we once custom fab any fitting.

But, AutoCAD MEP can do this but it takes some effort and manual calculation. In this particular case, you'd have to use precise custom fittings to start with. Still... it's not an automatic process. But things like rolling offsets, oh yeah... AutoCAD MEP can do all day long.

You need a pipe fitters handbook. I no longer have mine, but maybe one of your shop guys have one. Most of the info should be in there.

When I did pipe fitting, I just used a pipe wrap, as I recall, I never recieved very good drawings for this type of stuff.

Cutting the fitting is not the problem, that's basic stuff, it's calculating the fitting angle(s) needed to turn a pipe run at and odd angle while changing elevation at the same time. I've been fitting pipe for 24 years and I've never seen a method to solve Option1 in any pipe fitters book. It's been trial and error, be it in the field or sitting at a cad station. I was thinking it's time to learn the easy way. Lets not focus on the logistics, just think of it as a math or cad problem of how to maintain continuity between lines of different angles and different elevations using two arc segments.

I gotcha. Well, unfortunately I've never seen AutoCAD MEP be able to do this in the exact scenario you've mentioned. That is, custom cut-back, and rolling the fittings, to reach the proper angle and elevation at the same time. What AutoCAD MEP can do, is much simpler mathematical equations, such as rolling offsets. This is achieved by having both pipes preset. You'd have to manually calculate the cut back if you need exact fittings (such as 45s). Once they are in place, select one pipe and right-click on the Add Pipe grip, then use the "Add Selected" tool. Select the other end of the pipe and it auto-calculates the route and fittings. Well, it'll give you some options, but the rolling offset is in fact there.

That's as good as I've ever got AutoCAD MEP to do.

*EDIT*

Maybe play around with the tool I've mentioned above. I've never had the need for these types of pipe routing so it just may do something for you.

I'll start of by saying I have no engineering/pipefitting background, so I based the bends on a centre line radius, and cut them off at exactly 45°. But with trial and error came up with Option 3 two 45 bends and a straight section between of 8-1/4". The bends are blocks and have a rotation parameter, surely someone with a program like inventor could come up with a method to link all this using constraints. It may not all line up perfectly, but I bet its close.

Pipes.dwg

Putting a rotation parameter on the 45 elbow is clever, and I'll probably use that in the future if I can't find a calculated solution. I think constraints would be just the ticket in a program that could apply them in 3D.

Option3 is preferable to Option2, but Option1 is really what I want to solve. Unfortunately, it appears to be the most difficult to solve.

http://www.pipefittercalculator.com/

I use more often than I thought I would. Best 6 bucks I ever spent

Thanks for the reply. That looks like an awesome app for fitters, and I'll no doubt download it as the graphical interface seems like it would be much easier to use than a PipeTradesPro calculator, but it still does not appear to have the capacity to solve the initial problem.

How do I model (or calculate) the fewest welds/fittings required to change angle and elevation in a pipe run, as shown in Option1 below.

 

For this example the constants are: 8" standard steel pipe, one of the fittings is a standard butt weld 45 (12" radius), bend angle is 70 degrees, and the elevation change is 9". The custom fitting is cut from a standard 8" long radius 90.

 

Note: Option2 is just shown for reference, I'm only interested in solving Option1

 

[ATTACH=CONFIG]42336[/ATTACH]

Easy easy think again just a clue go 2d and.........

Easy easy think again just a clue go 2d and.........

It may well be easy, but it has stumped me for far too long. Maybe if you provided the precise angle of the 2nd fitting I could work it backward.

It may well be easy, but it has stumped me for far too long. Maybe if you provided the precise angle of the 2nd fitting I could work it backward.

Other clue 2 items at a time and...........

....a PipeTradesPro calculator....

Easy solved think again go 2d wysiwyg 2 items at a time clue is views generated.

Until the next clue try it.

And let us know because it's an easy fix here remember folks sometimes been there and seen it when it's your daily bread.

Other clue 2 items at a time and...........

I'm not interested in playing games, so unless you can provide the precise angle for the question proving that your technique works, I'm not that interested. And for the record, the parameters in the first post (70 degrees with 9 inches rise) are of no particular significance, it is simply a sample problem... it could be any angle less than 90 degrees and any elevation change less than 12 inches (8" 45LR + 8" 90LR = 12" rise)

Man I have mine stored away somewhere. This just reminded me I wanted to dig it up since I am in need of it again actually.

 

I really don't use mine that much because it's difficult to remember the sequences without referring to the manual. I usually just grab a regular calculator and my fitters book with the trig tables in the back. The graphical pipefitter app seems like it might send mine into full retirement.

Ha, yeah... those little smart phonez are taking all the glory nowadays. Best part of that calculator is fractional feet and inches calculations for easy elevation differences. Granted, AutoCAD calculator does it but just so much easier to grab that bad boy and be done with it.

I liked using it for AutoCAD MEP to give me real-world accurate cut backs on my rolling offsets to mimic field installation, but now that I'm Revit only now, it does it already.