Determining Wall Thinning When Bending Pipe 2

[cbrock]

I would like to determine what the minimum bend radius would be required when bending pipe.

The B31.3 code does not specify a minimum radius but does give formulas to calculate the minimum required thickness of the intrados and extrados after bending. Once can back calculate the minimum radius if the intrados and extados thicknesses were known.

Does anybody know how (if possible) to calculate the change in thicknesses would be prior to bending the pipe?

If it helps, I am dealing with both 1/2" and 3/4" Sch 80 stainless steel pipe.

Thanks in advance.

 

[athomas236]

You may find that the best way is to make some tests since thinning can depend of the equipment used and the bending process, ie either hot or cold bending
athomas236

 

[reichertc]

cbrock,

Here are some "worst-case" thinning percentages that I have received from local pipe bending shops in the last couple of years. May vary for material and diameter of pipe. I'd think that these numbers are coming from a acomparison of the straight length of pipe to the bent length, and would assume that the bent metal would have the same density as the sraight metal, but I've never really looked at that too hard.

3D - 18%
5D - 12.5%
10D - 8%

Personally, I spec out what pressure rating I want for the bend, what wall thickness the buttweld ends should have, and let them figure out what wall thickness of pipe to start with.

Hope that helps some

 

[waskillywabbit]

In bending pipe it has been my experience for calculations that if you allow for a 15% thinning of the thickness you are covered.