reverse engineering volume

[junfanbl]

Hello, I am wondering if somebody can help provide me a new way to find the fluid volume of pipes.
Typically I would model a pipe to spec inside NX and find the fluid volume by subtracting the volume of the inner diameter from the volume of the outer diameter. However, this can approach can take time if you have dozens of fittings to calculate. What I want to do is, instead of going through the trouble of modeling to spec, I would much rather take a partially modeled fitting and reverse engineer the volume.

What I mean is, If I have an elbow that has an outer diameter of 4.5 (in^2), and a wall thickness of .1(in^2), and for example sake, a fluid volume of 75(in^2). I need to add a wall thickness of .5 to get the correct volume. Instead of adjusting the model, can we just adjust the volume to accurately reflect a change in the geometry?

 

[MikeHalloran]

If it makes that much of a difference to you, you will be disappointed when you start assembling real fittings, that have substantial variation in wall thickness and interior and exterior geometry.



Mike Halloran
Pembroke Pines, FL, USA

 

[junfanbl]

Well honestly, it isn't my job to design fittings. However when our design department doesn't always design a fitting to spec, I have to go in and finish it to get the correct volumes. Most of the time, if it is a complex piece I won't bother due to time constraints. So I was hoping to find a faster way to get the job done.

 

[someguy79]

In a typical system, I would just find the expected ID, compute cross sectional area, and multiply that area by the pipe length. Rarely is anything more sophisticated required or accurate. Notable exceptions to pipe volume are when the pipe run consists of short runs of straight pipe with a lot of fittings or valves.

What you're doing makes sense from an analytical perspective. In the field, you'll probably see enough variation due to construction and fabrication to throw it off. Then the difference in accuracy between the method I described, and the one you described might not be much.

 

[MikeHalloran]

Almost nobody designs their own pipe fittings.
My point was that when you get the 'same' fitting from multiple sources, you may find substantial differences in leg lengths and in the interior and exterior dimensions.
... and hence the interior volume.

I'm sure you can reverse engineer your model fittings to a particular volume, but I'm perplexed how you'll know what the 'real' volume of a real fitting is, except to trust some salesman (bad idea) or to measure a sample, which is subject to its own set of uncertainties.




Mike Halloran
Pembroke Pines, FL, USA

 

[junfanbl]

So basically you guys are saying I shouldn't be so critical about getting the volume spot on? I do understand that the volume I put down on paper and the actual volume will vary. Especially considering the size of some of the systems that we design, it almost isn't worth trying to calculate perfectly accurate volumes. Typically I will use someguy79's method to quickly find volume and weight to piping systems, and even fittings that are small. However, when I encounter large fittings; it is important to calculate more accurate numbers. Otherwise our weight estimates will be too far off.

 

[zdas04]

What exactly are you trying to accomplish? If it is a pipeline hydrotest, square the nominal pipe size (in inches) and the result is the fill volume (in barrels). This bit of coincidence results in a number about 8% bigger than actual, but that generally works out very sweet for spillage and trucks that don't get quite full.

If it is calculating weight on pipe supports then use ID to get cross sectional area and multiply times length and then double it.

If you are trying to calculate a fluid inventory, just use ID and length, the data quality will never be good enough to get a better estimate.

In other words, almost nothing we ever do with pipe requires the precision you seem to be looking for.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[IFRs]

"square the nominal pipe size (in inches) and the result is the fill volume (in barrels)" - I don't get it. Is this volume per 1,000 feet of pipe?

 

[zdas04]

I knew I was leaving something out. I was in a hurry. Yes it is fill volume per 1,000 ft of pipe. Pretty useful coincidence in the unit conversion.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist