'U' Bend of process coil for water bath heaters

[nvr]

We are designing a Indirect type heaters (water bath heaters) to API 12k.

API 12 K did not specify clearly whether the process coils of 'U' pipe to be formed by bending from straight pipe or welding of standard 180 degree return bend to straight pipes to form the 'U' coil.

Is the welding of standard 180 degree bend ( pipe fitting 1.25 times the diameter) to straight pipes to form a 'U' coil is advisable or need to be bent from straight pipe without weld joint.
Appreciate your response.
Thanks
N.V.R

 

[johnp]

My feeling is that it depends on the pressures you are working with. At low pressures there is no problem using standard 180 deg return bends. They are often used in commercial heat exchange units.

At higher pressures there are problems with welding which may cause you to use bent pipe coils.

 

[TD2K]

JohnP, would you bend pipe to a 1.25x diameter? It struck me when I first read this post that's a pretty tight radius to bend piping to? Heck, I'm not even sure I'd want to bend tubing to that trpe of a radius but this isn't something I'm real familar with.

 

[johnp]

TD2K
You are right. A stock short-radius bend is 2 X Pipe Size centre to centre for 180 deg turn. Hot bending would need a bending radius of 3 X pipe size or better.

If you wanted anything tighter than that you would need to make your own tube plate casting or fabrication. It would be expensive, and not recommended.