Compared with elbows, bend will have tangent length if the customers need. The bend radius is larger than elbows`. When it is more than 2D, it is called bend. There are 3D, 5D, 7D, 10D bends. Below picture is 3D Bend with tangent length, angle is 45deg and 90deg.
Carbon steel 3D bend
These bends are packed by wooden pallet because of big volume.
As for manufacture standard, it is different from other Pipe Fittings. Its standard is ASME B16.49.
Materials are carbon, alloy and stainless steel. Wall thickness in common use is STD, XS and so on. With the development of the society, steel bends are widely applied in oil & gas transportation of pipeline system.