Calculating a rolling offset in a pipe configuration? 1

[reades]

Can anyone tell me how I would go about calculating/determining what my rolling offset would be for a change in elevation and centerline of a pipe run. The use of the rolling offset is due to space/clearance limitations.

Thanks,
Steve

 

[unclesyd]

I would suggest that you get a pipe fitters handbook if you are going to be working with pipe.

Essentially you draw a box and find the diagonal and angle of the run. If you can use 45° Ells the more the merrier.
Try this website.

http://www.pipefitter.co.uk/rollingset.htm

 

[TBP]

The simplest way is to use a framing square, for small offsets. Larger ones can be done using a tape measrure, and anything that makes a 90* angle - tool box, work bench, corner of a room, etc.

Ordinary 45* offsets, such as 8" (for example), can be done with a square. 8" down the blade, 8" down the tongue (use either the inside or outside scales for both - don't use the inside for one and the outside for the other), and measure across the diagonal with a tape. 11-5/16". Take away for the two 45*s, and that's the length that needs to be cut. For larger offsets, say 48", measure down the walls of a room each way from the corner. Lay the tape measure across the diagonal, and that's the centre to centre.

Rolling offsets need one more step. For small ones, a framing square is again the simplest way. An 8" roll with a 15" set laid off on a square will show 17" when measured across, diagonally. Multiply this dimension by 1.414.

17 X 1.414 = 24.038". This is 24-1/32", which will be the centre to centre dimension.

These examples are from "The Pipe Fitter's And Welder's Handbook" and the "Pipe Trades Pocket Manual", both by Thomas Frankland. The single best book I've seen on pipefitting the "Pipe Trades Handbook" by IPT.

To determine the roll and set dimensions (I remember "roll out" for horizontal component and "set down" or "set up" for the vertical component), measure from the center line of each pipe to a common reference. For the roll, it's usually a wall, beam, or an existing parallel line. Subtract the two measurements, and that's the centre to centre horizontal component. The set is obtained the same way, usually using the floor, or ceiling.

The percentage of people in the pipe trades who can't figure an offset is very large. The number of people who can't figure a rolling offset is HUGE. There are some ugly, ugly piping installations out there.

 

[TBP]

The actual author of the "Pipe Trades Handbook" is Robert A. Lee, and the book is published by IPT.

http://www.iptbooks.com

 

[anotherpipeguy]

Offset squared = roll squared x set squared

anyone concurr?

When I first began I already knew a lot about this, and after a while I knew nothing.

 

[TBP]

That is indeed the mathematically correct method. However, you're left with finding the square root of the right side of the equation. If you're in an office you can open a drawer or briefcase and pull out a calculator. Pocket calculators tend to have pretty short lifespans in pipe trades pockets or tool boxes. I can't think of a fitter or plumber (or anyone else, for that matter) who can calculate a square root without one. If you've got a tape measure & a piece of soapstone or a pencil (and how can you NOT, if you're running pipe), you can determine the centre-to-centre dimension for any offset using the corner of the railing on the manlift, the lid on the job box, or an inside corner of the room. A framing square makes it go a little faster. Simple is good.

 

[pipewelder1999]

I think
offset=sqrt(set^2+roll^2)
Travel=Offset x =1/SIN(FittingAngle)
Run=offset*1/tan(fittingAngle)
Takeout For Fittings=Tan(fittingangle/2)x NPS

I previously had a program in a HP 32SII calculator that I used while I watched my fitter unload his square and pipefitters handbook. In my opinion it was much faster than the squares etc but the batteries never failed on his squares !

Hope this helps

Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[TBP]

Have you had your HP 32SII drop out of your pocket when you're up on a 12' step ladder, had it bounce twice off the concrete floor, land in a puddle, and had it still functional? I bet not I know for a fact that Stanley "Contractor Grade" tape measures will. If it won't survive a landing like that, it's not much good on a job-site. Simple is good. Simple and tough is better.

 

[pipewelder1999]

TBP
No never a fall from that height though I have dropped a many tapes from that height or more.

Actually the face has seperated from the plastic case at the top. The LCD has quite a bit of weld spatter. And it has seen numerous falls from when I bend over. Still functions except when the batteries are dead.

In the past 5 or 6 years I have bought at least 6 tapes due to bent hooks broken tapes or failed return springs. I still have the same calculator and a spare I thought I would need long before now.

After deciding the amount of rise and roll I need, it takes 25 to 30 seconds to get the c to c travel and takeout for the fittings. Has your tape measure and square ever done that ? I do have a Pipe Trades handbook along with all of IPT's other handbooks. I value them much more than a calculator. Howevr the amount of time it took me to learn how to program the calculator was small compared to the hours lost waiting for a fitter.

Take the task of calculating the takeout for a 36 degree elbow. Is that done with a tape measure ,is it calculated, or is it looked up ? From the time I know thats what I need using any calculator with trig functions it takes maybe 5 seconds. It takes at least that long to lookup the tangent of 36 degrees if you had your handbook already out. If there is a faster way to do this without a calculator, let me know.

In the construction trades I'm sure your view is held by most and will continue to be that way for some time. The most efficient way to do a job is always the most efficient way. That method may not be efficient for all.

Thanks and Have a good day


Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com