Table 5-4 is a guide to the designer who must specify wall thickness for
ordering pipe or tube. In general, it has been the experience that when good
shop practices are employed, the minimum thicknesses of straight pipe and
tubing shown in Table 5-4, should be sufficient for bending, and still meet
the minimum thickness requirements. The bend thinning allowance in table 5-4
may be provided in all parts of the cross section of the pipe or tube
circumference without any detrimental effects being produced.
When fully annealed tubing is bent, the increase in tensile strength due to
work hardening normally offsets the loss in wall thickness due to thinning.
For fully annealed tubing only, the bending allowances in table 5-4 may be
reduced or eliminated if the fabricator can demonstrate by actual test that
the bending procedures used do not reduce the tubing burst pressure below a
level 4.5 times the MAWP for the tubing. Tubing bent in this manner shall
not be annealed following bending.
For ferrous pipe material, when the radius of a bend is 5 nominal pipe
diameters or greater, and the nominal wall thickness of the pipe is schedule
40 or thicker the difference between maximum and minimum diameters shall not
exceed 8% of average measured outside diameter of the pipe before bending.
Greater flattening may be permitted or less flattening may be required by the
design, depending upon the service, the material, and the stress level
involved.
TABLE 5-4
Wall Thickness for Bending
Min. Thickness
Radius of Bends
Recommended Prior to
(Note 1)
Bending (Note 2)
6 pipe diameters or greater
1.06 tm
5 pipe diameters
1.08 tm
4 pipe diameters
1.14 tm
3 pipe diameters
1.25 tm
Note 1: Interpolation is permissible for bending to intermediate
2: tm is minimum wall thickness in inches (millimeters).
3: Pipe diameter is the nominal diameter as tabulated in ANSI
Standards B36.10, Tables 2 and 4, and B36.19, Table 1. For
pipe with a diameter not listed in these tables, and also
for tubing, the nominal diameter corresponds with the
outside diameter.
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