FIELD OF INVENTION

The present invention relates to a method of manufacturing clamping tools for
bending of non standard pipe sizes in induction pipe bending machine. More particularly
the invention relates to a method of manufacturing clamping tools required for carrying
out hot bending operation on metal pipes by means of an existing heating machine and
provides a new methodology of fabricating clamping tools for new or non-standard pipe
sizes in the manufacture of pipe bends used in power plant piping systems for carrying
water and steam of elevated temperature and pressure.
BACKGROUND OF THE INVENTION
Power plant piping systems consist of a number of bent metal pipes of different
angles and radii in the layout design. The sizes vary from pipe outer diameter (POD)
168 mm to 1016 mm, with different thickness requirement based on the temperature
and pressure of the medium i.e. water or steam, flowing through the pipes. The metal
pipes are of different materials viz. SA106 Grade B & Grade C, SA335 P12, P22, P91 and
P92. The pipe bends are formed by means of an induction heating machine that is
capable of bending various sizes (Diameter, thickness, angle, radii, arm lengths etc. as
shown in Figure 1). The metal pipes are heated by means of an induction heating

arrangement to a temperature, at which the yield strength of the metal is
approximately ten percent of the yield strength of the metal at room temperature, thus
enabling easy deformation during bending. Normally, the temperature range is between
770 to 1050 Deg. Celsius. Bending takes place by means of pusher unit, which pushes
the pipe from the back and a bending arm that traces a path of set radius. The pipe is
to be clamped on the bending arm side and to be supported on the pusher unit by
means of clamping tooling, which is unique for outer diameter of the pipes. The pipe to
be bent is clamped on the machine by using a set of eight clamping pads, whose inner
radius will be equal to the radius of the pipe (Outer diameter of the pipe, divided by
two) on the bending arm. On the pusher side also the pipe needs to be supported by
either a set of two or four clamping pads, or by means of a set of side and bottom
support plates, which are unique for pipes of different outer diameters. The machine
has been supplied with a range of clamping tooling for standard pipe sizes. Whenever
new or non standard pipe sizes are called for by the layout design, new set of clamping
tooling is required for enabling the machine to carry out bending. With the advent of
once-through super critical technology a variety of new pipe sizes, particularly inner
diameter (ID) controlled pipe sizes are encountered in the piping systems. For bending
these new pipe sizes, new clamp tooling is required to be fabricated. The usual
procedure for fabricating the clamping tools is from plates that are either bent to the
required size or cut and machined from carbon steel plates. The disadvantages in this

method include material wastage, time consumption, need of fixture to maintain the
circularity etc. This invention pertains to a method of fabricating clamp tooling from
circular work pieces that are usually available as off-cut pieces of metal pipes of
diameter higher than that of the pipe, for which the clamping tools are fabricated. This
economical and innovative method can be used to fabricate clamping tools at shop floor
for any new size of pipe that is encountered as per the layout design and enhances the
capability of the bending machine, enabling it to produce any size within the size range
specification of the machine.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a method of manufacturing
clamping tools for bending of non standard pipe sizes in induction pipe bending
machine, which is simple, quick and cost-effective method of fabricating a set of
clamping tools for any new and non standard pipe sizes required to be bent using
induction bending machine.
Another object of the invention is to propose a method of manufacturing
clamping tools for bending of non standard pipe sizes in induction pipe bending
machine, which fabricates clamp tooling from circular work pieces available as off-cut
pieces of metal pipes of diameter higher than that of the pipe.

SUMMARY OF THE INVENTION
In accordance with the objective to fabricate clamping tools from circular work
pieces (ref. Figure-3) that are available as off-cut pieces of metal pipes, depending on
the size of the pipe to be bent, suitable off-cut pieces of diameter higher than that of
the pipe has to be identified. The identified off-cut material should be then cut to the
required length, depending on the width of the clamping pads required to seat on the
bending machine adaptor. The inner diameter of the work pieces should be then
machined to seat on the curvature of the pipe to be bent. The outer diameter is to be
machined to seat on the curvature of the machine adaptor. For example, in order to
manufacture clamping tooling for bending a pipe of outer diameter 792mm, off-cut pipe
of outer diameter 864mm and thickness 42 mm was chosen. The inner diameter of the
offset piece will be 780mm, which has to be machined to 792mm, in order to seat and
clamp on the curvature of the pipe of OD 792mm. The machined work pieces are then
cut in to four segments [1] (ref. Figure 4) and mounting lugs [2] are welded on to the
segments. Depending on the machine configuration the no. of sets of clamping pads for
bending arm side clamp and pusher arm side are to be chosen.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to the invention,
Fig. 1 : shows the schematic diagram of a metal pipe bend.
Fig. 2 : shows the schematic diagram of metal pipe bending using the induction
heating process.
Fig. 3: Shows the schematic diagram of the work pieces for fabricating the
bending arm side and pusher arm side clamps.
Fig. 4: Shows the schematic diagram final welded assembly of the clamping
Insert.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Figure 1 shows the schematic diagram of a typical metallic pipe bend used in
power plant piping systems. Forming the pipe bends is carried out using a specialized
process called induction bending, schematic of which is shown in Figure 2. The process
involves clamping of the pipe to be bent on a radial arm and applying pushing force
from a pusher unit located at the back of the machine, while the pipe passes through a
narrow section of heated band. The applied bending moment causes deformation at the

heated zone. For carrying out bending, rigid clamps are required at the bending arm
side and pusher arm side for clamping the pipe to be bent. For every new outer
diameter of the pipe to be bent, new set of clamping tools are required. Whenever new
pipe sizes are required to be bent, a new set of clamping tools are to be fabricated. In
order to fabricate clamping tools from circular work pieces (ref. Figure-3) that are
available as off-cut pieces of metal pipes, depending on the size of the pipe to be bent,
suitable off-cut pieces of diameter higher than that of the pipe has to be identified. The
identified off-cut material should be then cut to the required length, depending on the
width of the clamping pads (1) required to seat on the bending machine adaptor. The
inner diameter of the work pieces should be then machined to seat on the curvature of
the pipe to be bent. The outer diameter is to be machined to seat on the curvature of
the machine adaptor. For example, in order to manufacture clamping tooling for
bending a pipe of outer diameter 792mm, off-cut pipe of outer diameter 864mm and
thickness 42 mm was chosen. The inner diameter of the offset piece will be 780mm,
which has to be machined to 792mm, in order to seat and clamp on the curvature of
the pipe of OD 792mm. The machined work pieces are then cut in to four segments
known as clamping pads[1] (ref. Figure 4) and mounting lugs [2] are welded on to the
segments. Depending on the machine configuration the no. of sets of clamping pads[1]
for bending arm side clamp and pusher arm side are to be chosen. The critical
dimensions in fabricating the clamping tools as given in Figure-4 are as follows. ‘ØD’

refers to the outer diameter of the clamp pads [1]. ‘ØD1’ refers to the inner diameter of
the clamp pads [1], which is equal to the outer diameter of the pipe to be bent, with
some allowance. ‘E’ refers to the pitch circle diameter of the machine adaptor, which is
a very critical dimension in positioning of the holes (h) on the mounting lugs [2]. ‘L’
refers to the length of the mounting lug. ‘B’ refers to the breadth of the mounting lug.
‘H’ refers to the hole diameter in the mounting lug, through which the mounting pins
pass through. To ensure the alignment of the mounting holes, with the pins the welding
of the mounting lugs are done by positioning the clamping pads and mounting lugs on
to the machine adaptor and aligning them with pins, after which welding is done as
shown in detail A of Figure-4.

WE CLAIM
1. A method of manufacturing clamping tools for bending of non standard pipe
sizes in induction pipe bending machine, the said method comprising;
identifying off-cut pieces of diameter higher than that of the pipe to be bent;
cutting the said identified material to the required length depending on the width
of the clamping pads (1) required to seat on the bending machine adapter;
machining the inner diameter (ØD1) of the said material to seat on the curvature
of the pipe to be bent;
machining the outer diameter (ØD) of the said material to seat on the curvature
of the machine adapter;
cutting the machined workpieces / material into four segments or clamping pads
(1);
welding mounting lugs (2) on to the segments;
wherein the holes made on the welded mounting lugs (2) are disposed on a pitch
circle diameter (E) of the machine adapter when mounting pins pass through the said
holes wherein the alignment of the mounting holes with pins is ensured by welding the
mounting lugs by positioning the clamping pads (1) and mounting lugs (2) on to the
machine adapter after being aligned with pins.

2. The method as claimed in claim 1. wherein the outer diameter of the clamping
pads (1) seat on the bending machine adapter.
3. The method as claimed in claim 2, wherein the inner diameter of the clamping
pads (1) after machining, seat on the curvature of the pipe to be bent.