FIELD OF THE INVENTION
The present invention relates to an improved method of purging inert gas into
rotating steel tubes during a process of gas shielded butt welding of the tubes to
eliminate root oxidation of weld metal and adjacent region in the materials The
invention further relates to a device for purging inert gas inside weldable tubes
to produce improved quality of welding.
BACKGROUND OF THE INVENTION
In the fabrication process of supercritical boiler, tube material such as Super
304H, T92 are used. This is used in the super heater and reheated areas of the
boiler system for transferring the superheated steam. The primary objective of
this assembly is to increase the steam temperature in the supercritical boilers.
For the superheaters, Super 304 tube material is used and butt weldable by MIG
welding through external purging. Initially it was observed that the problem of
root oxidation in the internal diameter (ID) of the tube butt joint. In order to
avoid the problem of root oxidation, it was recognized by the inventors that
purging of the argon gas in the ID of the tube ensures an effective shielding
gas atmosphere which interalia eliminates root oxidation of the weldment in the
ID of the weld metal without affecting a normal production rate of at least about
60 joints per shift. However, it was noted the MIG butt welding is performed by

rotation of the tube against the stationary torch on the top over of the joint
which calls for an innovative device for purging of ID of tube and is
simultaneously capable of working against the rotating stainless steel tubes
during the welding.
Korean Patent ( No.: KR 20080095285) describes a purging apparatus for inner
purging using a camera for locating the position, and at least one airbag opens
and closes the both ends of the welded pipe while the airbag being shrunk and
expanded by air. A traveling part transfers a purging device to an internal
position of the weldable pipe. But this is more cumbersome to use in boiler tube
welding applications.
Korean Patent (KR 20100009351) discloses a purging apparatus to maintain a
desired position by expanding or contracting the airbags uniformly. The gas
supply and exhaust parts supply including the discharge to the pipe inside the
purging gas is done through gas supply and exhaust ports. A controller controls
the amounts of air supply/exhaust and gas supply/exhaust. The left and right
guide rollers move inside the welding pipe.; The left airbag and the right airbag
are connected by umbrella rib links. But the setting time involved is quite high.

SUMMARY OF THE INVENTION
Accordingly, in a first aspect of the invention, there is provided a device for
purging inert gas into rotating tubes during a process of gas - shielded butt
welding of the tubes to eliminate root oxidization of weld metal and the adjacent
regions comprising a purging gas spray distribution located adjacent the
weldable joint; a purging gas hose attached to the distributor and axially
extending backwardly through the inner diameter upto the tube inert; an outlet
hose connector nipple having a first end and a second end, the first end
of the nipple connected to the distal end of the purging hose, and the second
end of the nipple connected to the stepped Teflon adaptor which is sealingly
connected to the tube inlet; and a bearing with a bearing adaptor and a
bearing nipple disposed inside the teflon adaptor to allow supply of purging
gas from a gas source to the bearing nipple through an inlet hose connector
nipple brazed to the bearing adaptor wherein the gas spray distributor
regulating the gas flow in all directions of the weldable joint to eliminate root
oxidization.
In a second aspect of the invention, there is provided a purging device to
ensure inner diameter purging for long length tube which are rotated and butt
welded by gas shielding welding process. The device is a mechanical connecting
assembly for transfer of purging gas from a gas source to the inner diameter of

the tube butt joint which is located from one end of the tube to about more than
08 metres length. The device comprises a bearing adopter through which the
purging gas is passed through the rotating tube inner diameter till the location
just about 200 mm away from the weld joint. This saves the consumption of
purging gas as it is confined to a narrow region of 200 mm on either side of the
joint. The method and device is simple to use for production of butt joints of
super 304, as it takes less than 30 seconds for setting up the purging device for
each joint and filling up time less than 5 seconds and root oxidation defects in
stainless steel grade of materials, is eliminated.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved method of
purging inert gas into rotating steel tubes during a process of gas shielded butt
welding of the tubes to eliminate root oxidation of weld metal and adjacent
region in the materials.
Another object of the invention is to propose an improved method of purging
inert gas into rotating steel tubes during a process of gas shielded butt welding
of the tubes to eliminate root oxidation of weld metal and adjacent region in the
materials, which improves the productivity and quality of the welded joint.

A still another object of the invention is to propose a device for purging inert gas
into rotating tubes during a process of gas - shielded butt welding of the tubes
to eliminate root oxidization of weld metal and the adjacent regions.
These and other objects and advantages of the invention will be apparent from
the ensuing description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 - shows an inert gas purging device according to the invention.
DETAIL DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
As shown in figure 1, a purging gas spray distributor (8) is locatable nearer to
the weld joint. From the spray distributor, a purging gas hose (7) is drawn
throughout a long tube inlet. An outlet hose connector nipple (6) is connected to
the purging hose (7) end. Other end of the nipple (6) is connected with a
stepped Teflon adaptor (4) such that the adaptor (4) can be tightly fitted to the
various sizes of tube inlet ends. For avoiding rotation of the purging device, a

bearing (5) is set in the ID of the Stepped Teflon adaptor (4) . Purging gas is
supplied from a cylinder to a Bearing nipple (2) through an inlet hose connector
nipple (1) brazed with the bearing adaptor (3).
While welding, gas flows from the cylinders to weld area through the inlet Hose
Connector Nipple (1), the bearing Nipple (2), the bearing (5), the outlet hose
Connector Nipple (6), the purging Hose (7), and the Gas Distributor (8). Gas
distributor (8) is used to regulate the gas flow in all directions. This gas acts as a
purging gas, eliminating root oxidation and given sound weld. This system is
easily detachable and attachable within 30 seconds.

WE CLAIM:
1. A device for purging inert gas into rotating tube during a process of gas -
shielded butt welding of the tubes to eliminate root oxidization of weld
metal and the adjacent regions comprising a purging gas spray
distribution (8) located adjacent the weldable joint; a purging gas hose
(7) attached to the distributor (8) and axially extending backwardly
through the inner diameter upto the tube inlet; and outlet hose connector
nipple (6) having a first end and a second end, the first end of the nipple
(6) connected to the distal end of the purging hose (7) and the second
end of the nipple (6) connected to a stepped Teflon adaptor (4) which is
sealingly connected to the inlet; and a bearing (5) with a bearing adaptor
(3) and a bearing nipple (2) disposed inside the Teflon adaptor (4) to
allow supply of purging gas from a gas source to the bearing nipple (2)
through an inlet hose connector nipple (1) brazed to the bearing adaptor
(3), wherein the gas spray distributor (8) regulating the gas flow in all
directions of the weldable joint to eliminate root oxidization.
2. The device as claimed in claim 1, wherein the bearing adaptor (3)
terminates the supply of purging gas at a predetermined location away
from the welding joint.

3. The device as claimed in claim 1, wherein the device is enabled to
complete butt joint of stainless steel, super 304 grade within 30 seconds.

ABSTRACT

The invention relates to a device for purging inert gas into rotating tubes during
a process of gas - shielded butt welding of the tubes to eliminate root
oxidization of weld metal and the adjacent regions comprising a purging gas
spray distribution (8) located adjacent the weldable joint; a purging gas hose (7)
attached to the distributor (8) and axially extending backwardly through the
inner diameter upto the tube inlet; an outlet hose connector nipple (6) having a
first end and a second end, the first end of the nipple (6) connected to the distal
end of the purging hose (7), and the second end of the nipple (6) connected to a
stepped Teflon adaptor (4) which is sealingly connected to the tube inlet; and a
bearing (5) with a bearing adaptor (3) and a bearing nipple (2) disposed inside
the Teflon adaptor (4) to allow supply of purging gas from a gas source to the
bearing nipple (2) through an inlet hose connector nipple (1) brazed to the
bearing adaptor (3), wherein the gas spray distributor (8) regulating the gas flow
in all directions of the weldable joint to eliminate root oxidization.