FIELD OF THE INVENTION:
The present invention relates to a novel argon purging device in butt joint
welding for high chromium alloy steel pipes or more particularly relates to a
device which can be used for concentrating of argon at root area of welding and
also a methodology of purging the atmospheric air through the inert gas argon
at butt welding of high thickness pipes of high pressure steam generators.
BACKGROUND OF THE INVENTION:
In high pressure and high temperature steam generator, the piping system
forms an integral part. Piping systems involve welding between pipes for
routing of high pressure high temperature steam. Pipes of alloy steel material
are welded to each other by butt joints. The butt joint involves root welding
using GTAW (Gas Tungsten Arc Welding) process. This welding process calls for
inert atmosphere, so that oxidation is avoided. One such process for creating
inert atmosphere is purging through argon. The argon gas forms an inert
atmosphere so that oxidation may be avoided.
The butt joint root welding of high chromium alloy steel pipes carried out by
manual Gas Tungsten Arc Welding (GTAW) requires shielding from atmospheric
oxygen. Otherwise, Chromium reacts with oxygen and forms Chromium Oxide
(CrO2) which is termed as oxidation. Oxidation occurs in the root weld seam if
atmospheric air or oxygen is present near the weld portion. The top or outer
layer of weld is shielded by argon through the welding torch & the bottom or
inner layer of weld is backed by argon supplied through the inner region of the
pipe. The outside diameter of the pipe varying from 508mm to 610mm and the
thickness of the pipe ranging from 26mm to 100mm. The length of each pipe is
approximately 6000mm.
Argon which is heavier than air is used to purge out the atmospheric air or
oxygen from the inside of the pipe. The specific gravity of argon is 1.38 times
heavier than air. Argon's relatively high density causes it to remain close to the

ground during gassing. Argon being inert or non-reactive nature doesn’t form
any inclusions in the molten weld metal.
Fig 4 illustrates the conventional method of argon purging as the argon gas is
fed into both ends of the pipe using two argon cylinders. The ends are closed
with metallic end covers. Once the argon is filled into the pipes, pressure builds
up inside the pipes. This pressure causes the argon to flow out through the root
gap, thus purging occurs. After setting the purging, the root of the joint is
welded by GTAW using the third Argon cylinder. Hence for welding a single butt
joint 3 argon cylinders are used at once.
After root GTAW welding, the joint is welded by 2 to 3 layers of SMAW & the
butt joint is completed by subsequent layers of SAW. Subsequently the job is
subjected to Post Weld Heat Treatment (PWHT) or Stress Relieving (SR). The
butt joints are then subjected to Radiographic test as per ASME Sec. V to meet
the code requirements of ASME Sec IX.
The inherent limitations of the conventional method of purging out the air from
pipe using the inert gas argon are:
> Ineffective purging at the butt joint location since argon being
heavier than air (1.38 times) settles at the inner bottom side of the
pipe
> More wastage of the inert gas argon, as it flows down from the pipe
through the root gap during the welding process, since the length
of the pipe is 6000mm on each side
> More release of argon to the atmosphere pollutes the working
atmosphere
> Incomplete fusion, lack of penetration and root oxidation occurs
leading to poor quality of butt joints
> Adverse effects of root oxidation are formation of weak brittle
structures in the GTAW root and uneven root weld

> Manual Grinding of oxidized root by a fitter crawling through the
length of the pipe in the inside diameter
> Additional welding, Stress Relieving, Radiographic Testing in case
of thickness reduction
> Difficulty in grinding at inaccessible area and multi-planar jobs
Hence there is a need for a much more effective method of argon purging to
overcome the above-mentioned difficulties.
The present invention meets the above-mentioned need.
SUMMARY OF THE INVENTION:
An apparatus for argon purging at the butt joint welding comprises; a semi-
circular guide tube for providing shield at the root of the joint; a bent tube with
drilled holes fixed at the centre of guide; a ceramic fibre cloth for ensuring
complete removal of leak of argon gas; a lifting mechanism enclosed in a gear
box, further comprises four bevel gears; a small trolley for carrying the fixture;
characterized in that the shielding by said two tubes facilitates the
concentrating of argon gas at the root gap of the welding and thereby an inert
gas atmosphere can be created in the butt welding.
OBJECTS OF THE INVENTION:
It is therefore, the principal object of the present invention is to provide a device
for argon supply in butt welding of high chromium alloy steel pipe which
ensure substantially better shielding and hence results in complete removal of
root oxidation.
Another object of the present invention is to provide a device for argon supply
in butt welding, which facilitates concentration of argon gas within the root gap
of the butt welding so that uniform penetration in root can be achieved.
Yet another object of the present invention is to provide a device for argon
supply in butt welding, which can be positioned exactly at the butt joint area
and to can be operated it from the opening end of the pipe.

Further object of the present invention is to provide a device for argon supply in
butt welding, which seal the device with high temperature resistant materials
for ensuring zero leakage of argon.
Another object of the present invention is to provide a method for argon supply
in butt welding, which can accommodate variable diameter and thickness of the
respective pipes.
Yet another object of the present invention is to provide a method for argon
supply in butt welding, which account for minimum losses yet highly efficient.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
It is to be noted, however, that the appended drawings illustrate only typical
embodiments of the present subject matter and are therefore not to be
considered for limiting of its scope, for the invention may admit to other equally
effective embodiments. The detailed description is described with reference to
the accompanying figures. Some embodiments of system or methods in
accordance with embodiments of the present subject matter are now described,
by way of example, and with reference to the accompanying figures, in which:
Figure 1 illustrates the argon purging device arrangement.
Figure 2 illustrates the details of the guide.
Figure 3 illustrates the arrangement of the device into in a pipe to pipe butt
welding.
Figure 4 illustrates the conventional method of Argon filling.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The present subject matter disclosed herein relates to a novel movable device
for purging argon in butt joint welding for elimination of root oxidation. The
said device basically used for concentrating argon at the root face welding
specially in case of butt joint welding of high chromium alloy steel pipes and
different types of high chrome high alloy material.

As explained above, the device mainly comprises a semi-circular guide (1) of
diameter ranging from 410mm to 450mm, according to the inner diameter of
the pipe for shielding the root of the butt joint, a bent tube (2) of OD 25.4mm
and ID 10mm with drilled holes (3), a ceramic fibre cloth (4) tightly held at the
edges and the corners of the guide to ensure that the guide is leak proof.
Further, the device also comprises a lifting mechanism enclosed in a gear box
(5), a dummy (10) and a small trolley for carrying a fixture (8).
The complete structure is illustrated in Figure 1.
The tube (2) is bent to the same radius as that of the guide and fixed at the
center of the guide (as shown in Figure 2).
Fig 2 clearly illustrates the bent tube (2) which has small holes drilled (3) for
smooth flow of argon and also a ceramic fibre cloth (4) for ensuring the
complete protection against leak of argon gas. The ceramic fibre is helpful to
give protection against high temperature such as 760°C and it is completely
leak proof.
Figure 1 illustrates a lifting mechanism which is used for lifting the guide and
provides complete shield of the butt joint from atmosphere. The lifting
mechanism is enclosed in a gear box (5) and comprises of four bevel gears.
The first gear (6) is connected to the tube (2) for rotation and act as a driver.
The second gear (7) is attached to the lifting screwed rod (11) which is fixed
through a nut and bolt mechanism. Another gear (10) which is placed opposite
to the driver can act as a dummy for future usage.
The argon is supplied through another tube (9) which is connected to the driver
and whenever there is need of more argon or the circumference of guide to be
increased, the same may be achieved through the dummy provided.
For easy movement inside the pipe, a small trolley is provided for the fixture (8).
For ease of assembly and servicing of gear box (5), it is closed with a plate of
3mm thickness.

After using the argon purging device, the butt joint Radiographic Test (RT)
reveals that there is no oxidation in root welding & uniform penetration in root
(as shown in Fig 3).
In one embodiment of the present subject matter, there is a method provided to
achieve better purging of argon in butt joint welding for high chrome high alloy
steel pipe comprising a lifting mechanism enclosed in a gear box (5), a dummy
and a small trolley for carrying a fixture (8).
The argon gas coming out from the cylinder travels through the tube (9) and
through the gears it enters to the bent tube (2), thereby comes through the
holes (3) and localized at the root of the butt joint effectively.
The argon purging device as claimed hereafter, has resulted in elimination of
root oxidation in high chrome high alloy steel pipe butt joint welding, improved
weld quality as well as reduced process time. The repeatability and quality of
joints are ensured through the usage of different guides for different diameter
pipes (OD 508, 558 and 610 mm). The introduction of this technology adds to
BHEL’s image for the use of state of art technology in turning out products with
enhanced and consistent quality.
The trolley set up is made to move the guide arrangement to the required area.
Moreover, the arrangement is made in such a way to accommodate variable
diameter and thickness by its respective guides. Thereby, we achieve the
required inert gas (argon) atmosphere for the butt welding process with much
reduced losses. The device developed consists of a mechanism that can localise
and concentrate argon gas effectively with minimal losses and high efficiency.
The method can be adopted for all high chrome high alloy pipe and header butt
joint welding and also can be used for different type of high chrome high alloy
materials.
Argon gas savings up to 87.5% (only one fourth of an argon cylinder is used in
place of 2 argon cylinders for purging one butt joint) & the overall cycle time is
reduced by 40% (Reworks are completely eliminated).

The non-limiting advantages of the invention are given below:
1- Improved safety for workmen (Rework grinding inside the pipe is avoided)
2- Reduced exposure of argon to the atmosphere
3- Safe & pleasant work atmosphere
4- Productivity was improved by 40%.
5- Improved Quality of the joints.
6- No root oxidation.
7- Reworks due to root oxidation eliminated.
8- Estimated cost savings per annum (Recurring) Rs. 85 Lakhs (Recurring)
9- Carrying additional Non-Destructive Tests and the costs associated with
them are eliminated.
10. Minimizes argon loses by localized and concentrating the inert gas argon.
11. The purging device accommodate pipes of variable diameter and thickness
that can withstand high temperatures.
The shielding by argon in the butt welding of two alloy steel pipes is achieved
by developing a movable device that localize the argon gas within the region
that is being welded. This localization and concentration is achieved by
developing a device that blows out argon through a guide into the root gap of
the welding. The blowing out of argon through the root gap causes purging of
atmospheric air for the welding process.

WE CLAIM:
1. An apparatus for argon purging at the butt joint welding comprises;
- a semi-circular guide (1) tube for providing shield at the root of the
joint;
- a bent tube (2) fixed at the centre of guide;
- a ceramic fibre cloth (4) for ensuring complete removal of leak of argon
gas;
- a lifting mechanism enclosed in a gear box (5), further comprises four
bevel gears;
- a small trolley for carrying the fixture (8);
characterized in that the shielding by said two tubes facilitates the
concentrating of argon gas at the root gap of the welding and thereby an inert
gas atmosphere can be created in the butt welding.
2. The apparatus for argon purging at the butt joint welding as claimed in claim
1, wherein the internal diameter of the semi-circular guide (1) tube (2) is 10mm.
3. The apparatus for argon purging at the butt joint welding as claimed in claim
1, wherein the bent tube (2) has various holes (3) drilled onto it for free flow of
argon.
4. The apparatus for argon purging at the butt joint welding as claimed in claim
1, wherein said ceramic fibre cloth (4) can provide protection upto a
temperature of 760°C.
5. The apparatus for argon purging at the butt joint welding as claimed in claim
1, wherein said ceramic fibre cloth is tightly held at the edges and corners of
the guide.
6. The apparatus for argon purging at the butt joint welding as claimed in claim
1, wherein the first gear is connected to the tube (2) for the rotation and second

gear is attached to the lifting screwed rod through a nut and bolt mechanism
(7).
7. The apparatus for argon purging at the butt joint welding as claimed in claim
1, wherein the gear box (5) is enclosed with a plate of 3mm thickness.
8. The apparatus for argon purging at the butt joint welding as claimed in claim
1 and 7, wherein the thickness of said plate is 3mm.
9. A method for achieving purging atmospheric air by the inert gas argon in a
butt joint welding comprises:

- joining of a semi-circular guide (1) with another bent tube (2) which has
drilled holes (3) for supplying argon;
- supply of argon from the cylinders though a tube (9) which is connected
to the root area of weld butt joint through the gear sets;
characterized in that the argon gas coming out from the cylinder travels
through the tube (9) and passed on the gears and eventually enters to the bent
tube (2), thereby comes through the holes (3) and localized at the root of the
butt joint effectively.
10. The method for achieving purging atmospheric air by the inert gas argon in
a butt joint welding as claimed in claim 9, wherein the third gear act as a
dummy which provide more argon gas when needed.