How to model a Pulled Bend and a does the AutoPIPE consider the thinning wall on the outer radius of a pulled bend?
A pulled bend is a bend that is formed by a machine wrapping the pipe around a shoe horn form (i.e. like a tubing bender bending tubing) and pulling the pipe against the shoe horn shape.
One side effect of bending the work-piece is the wall thickness changes; the wall along the inner radius of the tube becomes thicker and the outer wall (extrafit) becomes thinner. AutoPIPE does not consider the different wall thickness. The wall thickness is a uniform value specified on the pipe properties dialog screen.
Typically a Pulled bend's dimension for both Radius and Length of legs are larger than a standard forged / welded pipe fitting.
Example: model 90 deg Pulled bend with 3D radius and welded directly to butt-welded valve on both sides 2 feet (609.6mm) away.
Piping Code = ASME NB, NC, or ND:
Using AutoPIPE Nuclear version, with piping codes ASME NB, NC, or ND, suggest that the proper Bend radius value be entered or selected from the drop down listing (ex. select 3D) and set Bend Type = Pulled (ex. select Pulled).
insert valve 2 feet (609.6mm) away on both ends.
Question: Where to insert the Bend Weld Indices? at the valve locations or the Bend Near & Far node points?
Answer: at the Pulled bend weld locations. In this example, that would be at the valves.
Remember that a bend is made up of 4 node points: 1. Near, 2. Far, 3. TIP, 4. Midpoint
The Bend's Near and Far points are located based on the tangential distance for the specified radius to fit between intersecting lines. These points just so happens to coincide with standard practice for construction of a bend fitting to industry standards (ex. ASME B16. 9) for Short, Long, and xD bends. However a Pulled bend has legs on both sides that are typically much longer than a normal bend. Therefore, Pulled Bend weld indices should be placed at the actual weld locations, in this example, near the valve. The bend's Near and Far node points would be considered Straight pipe, i.e. no welds.
Note: if a USER SIF is placed at a bend's Near or Far node point, the program may list a warning in the Model Consistency Check report.
Piping Code = Non-nuclear codes
For other version of AutoPIPE, Standard or Plus (Advanced), using non-nuclear piping codes, to model a pulled bend, select Bend Type = "elbow", SIF and flexibility factor will automatically be calculated but suggest that Bourdon Pressure Effect be turned on (Tools> Model Options> Edit> "Include Bourdon rotational effect" check ON).
Bend & Miter Piping Components - Modeling Approaches