Minimum Pipeline Bend Radius

[jasperfizzle]

Hello,
Please i would like to know the accurate formula used in calculating the minimum pipeline bend radius and the steps involved.

Thanks,
Jasper.

 

[LSThill]

jasperfizzle (Mechanical)

Referenc:
PFIES-24 (Reaffirmed March 2001)
PIPE BENDING METHODS, TOLERANCE PROCESS AND MATERIAL REQUIREMENT
Prepared by Pipe Fabrication Institute Engineering Committee PFI.

Regards
Leonard Stephen Thill



L S THILL

 

[MJCronin]

jasper,

The minimum pipe bend radius is controlled by the code of record and the maximum amount of "wall wrinkling" and wall thinning permitted. Both cold bending and hot bending can be performed on piping

The amount of wrinking expected is a function of pipe diameter, wall thickness, bend radius, etc

ASME B31.1 and ASME B31.3 contain limitations on wall thinning and ovalization

More information here:

http://apexpiping.com/Es7.htm

MJC

 

[BigInch]

B31.4-2002 Liquid Pipelines has this to say

404.1 Straight Pipe
404.1.1 General
(a) The nominal wall thickness of straight sections
of steel pipe shall be equal to or greater than tn
determined in accordance with the following equation.
tn = t + A
(b) The notations described below are used in the
tn = nominal wall thickness satisfying requirements
for pressure and allowances
t = pressure design wall thickness as calculated
in inches (mm) in accordance with para.
404.1.2 for internal pressure. As noted under
para. 402.3.1 or para. A402.3.5, as applicable,
in setting design factor, due consideration has
been given to and allowance has been made
equations for the pressure design for straight pipe.
for the underthickness tolerance and maximum
allowable depth of imperfections provided for
in the specifications approved by the Code.
A = sum of allowances for threading and grooving
as required under para. 402.4.2, corrosion as
required under para. 402.4.1, and increase in
wall thickness if used as protective measure
under para. 402.1.
401.2.2), psi (bar)
Pi = internal design gage pressure (see para.
D = outside diameter of pipe, in. (mm)
S = applicable allowable stress value, psi (MPa),
in accordance with para. 402.3.1(a), (b), (c),
or (d)
404.1.2 Straight Pipe Under Internai Pressure.
The internal pressure design wall thickness t of steel
pipe shall be calculated by the following equation.
t = PD/2/S

404.1.3 Straight Pipe Under Extenial Pressure.
Pipelines within the scope of this Code may be subject
to conditions during construction and operation where
the external pressure exceeds the internal pressure (vacuum
within the pipe or pressure outside the pipe
when submerged). The pipe wall selected shall provide
adequate strength to prevent collapse, taking into consideration
mechanical properties, variations in wall thickness
permitted by material specifications, ellipticity (outof-
roundness), bending stresses, and external loads (see
para. 401.2.2).

404.2 Curved Segments of Pipe
Changes in direction may be made by bending the
pipe in accordance with para. 406.2.1 or installing
factory made bends or elbows, in accordance with para.
406.2.3.

404.2.1 Pipe Bends. The wall thickness of pipe
before bending shall be determined as for straight pipe
in accordance with para. 404.1. Bends shall meet the
flattening limitations of para. 434.7.1.

434.7.1 Bends Made From Pipe
(u) Bends shall be made from pipe having wall
thicknesses determined in accordance with para. 404.2.1.
When hot bends are made in pipe which has been cold
worked in order to meet the specified minimum yield
strength, wall thicknesses shall be determined by using
the lower stress values in accordance with para.
402.3.1 (d).
(b) Bends shall be made in such a manner as to
preserve the cross-sectional shape of the pipe, and shall
be free from buckling, cracks, or other evidence of
mechanical damage. The pipe diameter shall not be
reduced at any point by more than 292% of the nominal
diameter, and the completed bend shall pass the specified
sizing pig.
(c) The minimum radius of field cold bends shall
be as specified in para. 406.2.1(b).
(ci) Tangents approximately 6 ft (2 m) in length are
preferred on both ends of cold bends.

406.2 Bends, Miters, and Elbows
406.2.1 Bends Made From Pipe
(a) Bends may be made by bending the pipe when
they are designed in accordance with para. 404.2.1 and
made in accordance with para. 434.7.1.
(b) Except as permitted under para. 406.2.l(c), the
minimum radius of field cold bends shall be as follows:
Minimum Radius of
Nominal Pipe Size Bend in pipe Diameters
NPS 12 and smaller 18D
14 21D
16 24D
18 27D
NPS 20 and larger 30D
In some cases, thin wall pipe will require the use of
an internal mandrel when being bent to the minimum
radii tabulated above.
(c) Bends may be made by bending the pipe in
sizes NPS 14 and larger to a minimum radius of 18D;
however, bending pipe to radii approaching 18D that
will meet requirements in para. 434.7.1@) wiil be
dependent upon wall thickness, ductility, ratio of pipe
diameter to wall thickness, use of bending mandrel,
and skill of bending crew. Test bends shall be ma&
to determine that the field bending procedure used
produces bends meeting the requirements of para.
434.7.1@) and that the wall thickness after bending is
not less than the minimum permitted by the pipe
specification.

http://virtualpipeline.spaces.msn.com

 

[CarlB]

If you are referring to an elastic bend, such as a buried pipe layed with a radius, or evaluation of a pipe lowered into a trench, see Pg. 57 of this document:

http://www.crid.or.cr/crid/CD_Agua/pdf/eng/doc14612/doc14612.pdf