FIELD OF THE INVENTION
The invention generally relates to a method of manufacturing coils for reheaters
in high pressure steam generators for power generation. More particularly the
invention relates to a device for straight tube butt welding of shorter length
tubes of dissimilar materials in bulk quantity in known welding machines for
manufacturing reheater coils for high pressure steam generators.
BACKGROUND OF THE INVENTION
According to prior art, for joining tubes of outside diameter ranging from
31.8mm to 76.1mm, the conventional Tungsten Inert Gas(TIG) welding is used
for root run and subsequently finished with Metal Inert Gas (MIG) welding. For
mass production of welding of such tubes, the conventional straight tube butt
welding is used. But for welding of shorter lengths in huge quantity, in the
known welding machines is very difficult and additional resources is also
required.
Reheaters and Superheaters are manufactured with a combination of Stainless
steel and Alloy steels of T91 grade materials. When failure occurs at the
operating locations, it becomes very difficult for dissimilar welding at the power
generation site itself. This type of dissimilar welding for shorter length tubes is
very difficult in the conventional welding machine hence there is a need to
develop a device and a method to operate the known welding machines for
welding of bulk number of joints.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a device for straight tube
butt welding of shorter length tubes of dissimilar materials in bulk quantity in
known welding machines for manufacturing reheater coils for high pressure
steam generators,
A further object of the invention is to propose a method of butt welding in bulk
quantity shorter length tubes of dissimilar materials through known welding
machines.
SUMMARY OF THE INVENTION
Accordingly, there is provided a device for straight tube butt welding of shorter
length tubes of dissimilar materials in bulk quantity in known welding machines
for manufacturing reheater coils for high pressure steam generators. The device
consisting of a base member with a driving unit at a first end and a
corresponding matching tube holding unit at a second end. The driving unit is
connected with a rotating unit which in turn is connected to a tube holding
machine. This tube holding machine is connected to a compressed air hose for
cleaning purpose. The matching tube holding unit is fitted with at least three
rollers bearings with 120° each apart. Now a tube formed of stainless steel
material is inserted on the tube holding machine and the concentricity is checked
with three jaw chuck attached to the rotating unit The other tube formed of
dissimilar material, and which is to be welded with the matching tube, is inserted
in between said three rollers mounted on the matching tube holding unit. Now,
the matching tube holding unit is slided on the top of the base along with the

tube such that a root gap of 2mm is maintained. First, a tack weld is carried out
by intermittent rotation of tube holding machine using the controls provided on
the driving unit thereby the relative motion of the matching tube is obtained
which is attached to the matching tube holding. Now tube to tube welding is
carried out by conventional butt welding. The driving unit is having controls for
uniform rotation of the tube during welding process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig-1 shows a schematic arrangement of the device of the invention along with
the tubes and welding machine for welding.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Referring to the Fig 1, the device consisting of a strong base member (01) with a
driving unit (02) on one end and a matching tube holding unit (05) at the other
end. The driving unit (02) is connected with a rotating unit (03) which in turn is
connected to a tube holding machine (04). This tube holding machine (04) is
connected to a compressed air hose (08) for cleaning purpose. The matching
tube holding unit (05) is provided with at least three rollers bearings (09)
disposed 120° each apart. Now a tube formed of stainless steel material (06) is
inserted onto the tube holding machine (04) and the concentricity is checked
with three jaw chucks which is attached to the rotating unit (03). Another tube
(07) which is formed of a dissimilar material is to be welded with the matching
tube (06), is inserted in between said three rollers (09) mounted on the
matching tube holding unit (05). Now the matching tube holding unit (05) is

sliding on the top of the base (01) along with the second tube (07) such that a
root gap of 2mm is maintained. First, a tack weld is carried out by intermittent
rotation of the tube holding machine (04) using the controls (not shown)
provided on the driving unit (02) thereby the relative motion of the matching
tube (07) is obtained which is attached to the matching tube holding unit (05).
Now tube to tube welding is carried out by conventional butt welding machine
(not shown). The driving unit (02) is having controls (not shown) for uniform
rotation of the tubes (06,07) during the welding process.

WE CLAIM :
1. A method of dissimilar butt welding of shorter length tubes in bulk quantity
for manufacturing re-heater coils for high pressure steam generators in a
device, the device consisting of a base member (01) with a driving unit (02)
on a first end and a matching tube holding unit (05) at a second end, the
driving unit (02) being connected with a rotating unit (03) which in turn
connected to a tube holding machine (04),
the method comprising the steps of :-
- connecting the tube holding machine (04) to a compressed air hose (08)
for cleaning purpose,
- providing at least three rollers bearings (09) at 120° each apart to a
matching tube holding unit (05);
- inserting a tube (06) formed of stainless steel on the tube holding
machine (04) and checking the concentricity of the tubes (06) with at
least three jaw chuck attached to the rotating unit (03);
- inserting a second tube (07) formed of a dissimilar material and which is
to be welded with the stainless steel tube (06) in between the three
rollers (09) mounted on the matching tube holding unit (05);
- sliding the matching tube holding unit (05) on the top of the base member
(01) along with the second tube (07) such that a root gap of 2mm Is
maintained;
- tack welding the tubes (06,07) by intermittent rotation of the tube holding
machine (04) using the controls (not shown) provided on the driving unit
(02) thereby the relative motion of the matching tube (07) is obtained
which is attached to the matching tube holding unit (05); and

- conducting tube to tube welding by conventional butt welding machine
maintaining a uniform rotation of the tubes (06,07) during welding
process based on a control mechanism of the driving unit (02).