FIELD OF THE INVENTION
The invention relates to welding of pipes and tubes made of ferrous or non-
ferrous materials that require purging gas during root and hot pass welding.
BACKGROUND OF THE INVENTION
Root contamination is the common problem during welding of Alloy steels,
Stainless steels, Aluminum, Copper, Titanium, Zirconium, Molybdenum, Nickel
based alloys, and other gas reactive metals and alloys. Hot weld pool get
contaminated due to presence of oxygen which leads to numerous problems
such as root porosity, incomplete fusion and oxidized root surface. The resulting
oxidized surface remains no longer Corrosion-resistant and requires further
treatment. During welding of the plates, the oxidized surface can be removed by
mechanical procedures such as brushing, blasting, and pickling. In case of
welding of pipes it is difficult or impossible to remove the oxidized surface. To
prevent oxidation of the root, purging gas is used which removes the oxygen
present in the root. Commonly, argon is used as purging gas. Several methods of
purging are available. For small diameter pipes the ends of the pipes are capped
and the inert argon gas is allowed to purge the complete pipe section of the air.
For large diameter pipes both sides of the weld joint to be welded are plugged,
so that smaller area can be purged. Another method known is Inflatable Dam
arrangement as shown in fig 1.

According to this known method I the pipes are filled with purging gas .But the
method is not cost effective as large quantity of gas is wasted during the
welding. Although fiber glass tape and Water soluble plastic restricts the wastage
of purging gas, but has the limitations. Firstly the tape cannot be used for large
length of pipes. Secondly weld contamination cannot be avoided because of
mixing of adhesives at weld zone.
Various devices are known in the art for purging of gas during pipe welding.
US patent 4916281 teaches dynamics of flow rates of both shielding gas and
back-purging gas. The rates of gas flow in back-purging and in torch shielding
are controlled and a ratio between the flow rates is established.
US patent 4437710 shows inflatable type purging gas arrangement which creates
one each dam at either side of the weld. It consists of balloons which get inflated
when the purging gas enters into them and creates a sealed chamber which is
filled with the purging gas.
US patent 4723064 shows a purging gas arrangement for varying size of pipes.
A wing nut mechanism is created and inserted into the pipe end, and by
adjusting the mechanism the arrangement can be used for varying dimension
of pipe. Thus, the flow of the purging gas is always through the center.
US patent US 3994429 A teaches a purge unit for particular application when a
branch pipe is welded to a main pipe or a header. In all the discussed prior art,
an enclosed zone is formed in the vicinity of the weld root.

US patent US 20060068142 Al describes a welding tape and tape related
methods. An adhesive welding tape is positioned over the area to be welded and
a seal is created to generate an area free of air. But problems related to mixing
of adhesives with the weld zone are reported. No patent on impingement of
purging gas directly on weld root is found.
OBJECTS OF THE INVENTION
It is therefore an object of this invention is to propose an improved system for
gas purging in pipes and tubes which maintains an inert gas atmosphere within
the pipe during its welding.
Another object of this invention is to propose an improved system for gas
purging in pipes and tubes which maintains an inert gas atmosphere within the
pipe during its welding which creates an atmosphere of inert gas in the vicinity of
root of the weld.
A still another object of this invention is to propose an improved system for gas
purging in pipes and tubes which maintains an inert gas atmosphere within the
pipe during its welding which is simple and enabled to provide inert gas in a
controlled volume such that gas is available at forward and at trailing of the
weld arc.
Yet another object of this invention is to propose an improved system for gas
purging in pipes and tubes which maintains an inert gas atmosphere within the
pipe during its welding that can be used for varying diameter pipes.

A further object of this invention is to propose an improved system for gas
purging in pipes and tubes which maintains an inert gas atmosphere within the
pipe during its welding that rotates on its axis to purge the full weld diameter.
A still further object of this invention is to propose an improved system for gas
purging in pipes and tubes which welding which is cost effective and reduces the
cost incurred during purging in pipe welds.
Yet further object of the invention is to propose an improved system for gas
purging in pipes and tubes which can be novel from pipe end to the root of weld,
such that the system can be used for large length pipes
Another object of this invention is to propose an improved system for gas
purging in pipes and tubes which allows defect-free weld meeting the stringent
quality requirements.
SUMMARY OF THE INVENTION
Accordingly,.there is provided an improved system for gas purging in pipes and
tubes. As per the invention the weld root is purged by directly impinging the
purge gas in a controlled volume space. Envelop of gas is formed in a controlled
volume forward and trailing end of the arc providing a smooth purging during
the welding. Flow of gas is uniform owing to perforated gas exodus. Perforated
gas exodus has tube in tube mechanism through which its height can be
adjusted. A spherical wheel assembly passes through a circular spoke wheel and
has a telescopic mechanism which allows the system to be used for several

diameter pipes. The system assembly can be rotated through an external drive
mechanism in synchronization with the weld speed.
The system purges the weld zone by directly impinging purging gas on the root
of weld in a controlled volume space. This in-turn avoids the wastage of purging
gas and saves cost of welding. The system has the characteristics that it can be
used for series of diameter of pipes and tubes.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figures 1 and 2 - show the system of the invention.
Figure 3 - shows the gas exodus of the system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION
The system consists of the following items:
1. Perforated gas exodus (1), is ,a perforated sheet that distributes the gas
uniformly on the weld root. Its size is suitably selected to provide purging gas
forward and trailing of weld arc.
2. External tube (2) is welded with the gas exodus (1) and it helps in adjusting
the gap between the exodus (1) and ID of the pipe.

3. Internal tube (3) is also welded with the exodus (1) and a gas hose pipe is
connected to this tube (3).
4. Spoked wheel (4), provides inertia to the system during rotation. The external
tube (2) is threaded on the spoken wheel (4) and first and second telescopic
tubes (8, 9) are also mounted on it.
5. Spokes (5), provides strength to the spoked wheel (4). They are welded with
the spoked wheel (4) on one side and the guide tube (10) on another side.
6. Spherical Wheel (6), which touches with the ID of the pipe and provides a
spherical link between the pipe and full assembly.
7. U-Bend (7), provides rigidity between the spherical wheel (6) and the
telescopic tubes (8,9).
8. First Telescopic tube 1 (8) has external square threads on one side and the
spherical wheel and the U-bend are disposed on others side.
9. Second Telescopic tube (9), has internal square threads, matching with the first
telescopic tube (8) so that size of full assembly can be varied by fastening and
unfastening the threads. The telescopic tubes (8, 9) together constitute
telescopic assembly.
10. Guide tube (10), is a welded part that guides the gas tube with in itself. It is
used to manually move the whole assembly from the pipe end to its weld
junction. It acts as axis of rotation for the whole system.

The improved purging system has the characteristics of providing inert gas
atmosphere during the root welding of the pipes. The inert gas atmosphere is
created near the vicinity of the root of pipe to be welded. Inert gas comes out in
a uniform manner from the perforated gas exodus (1) designed in such a way
that an envelope of inert gas is created at onward and trailing of weld arc. The
perforated gas exodus (1) is welded with a tube in tube assembly, where the
external tube (2) is threaded to the spoked wheel (14) and gas hose is
connected with the internal tube (3). Gap between the gas exodus (1) and ID of
the pipe (2, 3) can be adjusted by tightening and loosening of threads. The
Spoked wheel (4) is the central hub of the system. The telescopic tubes (8, 9)
passes the spoked wheel (4) through screwing and unscrewing of the telescopic
tubes (8, 9) matches the spherical rollers (6) with ID of the pipe. Same
characteristic allows use of the system for range of diameters of pipe. To use the
system for purging gas, the tube is inserted through the guide tube (10) and
connected to the internal tube (3) on one side and a gas cylinder on other side,
-Telescopic tubes (8, 9) are adjusted so that the spherical wheels (6) touches ID
of, the pipes. The external tube (2) is also adjusted for a suitable gap in between
ID of the pipe and the perforated gas exodus (1). Whole system is inserted into
the pipe upto the root of weld manually by pushing the guide tube (10). Motor
mechanism is used to rotate the system along its central axis. Gas knob is
opened at the gas cylinder and gas is allowed to flow inside. Gas flow rate is
suitably maintained.

Approximate saving:
As per AWS D 10.11 For 5" diameter pipe 6 meters in length time for pre-purgim
is required for 200 min at a rate of 40CFH (18.8LPM). Assume welding is to tak
10 minutes.
As per conventional method total amount of gas required is approx. 4000 liters.
By proposed system pre purging time will be saved and amount of gas require
will be only during weld time thus approx. 200 liters will be consumed. Saving c
95% argon gas can be achieved.
One argon gas cylinder costs Rs 2500 .
With conventional system for making 100 welds 20 cylinders are required.
Total Cost of purging with conventional System 20x2500 = Rs 50000
With Proposed system for making 100 welds 1 cylinder is required.
Total cost with proposed system 1X2500 = Rs 2500.
Total amount saved in making 100 welds = Rs (50,000-2500) = Rs 47500

WE CLAIM :
1. An improved system for gas purging in pipes and tubes comprising
a gas exodus (1) for providing purging gas forward and trailing a
welding arc,
a tube assembly (2, 3) welded to the exodus (1), the tube
assembly having an external tube (2) adjusting the gap between
the exodus (1) and the pipe to be welded, and an internal tube (3)
having a gas hose pipe,
a first and a second telescopic tube (8, 9) having at a first side
respectively external and internal threads, the first telescopic tube
(8) at a second side bearing a spherical wheel (6) and a U-bend
(7);
a spoked wheel (4) providing inertia of rotation to the system and
threadly connected with the first and second telescopic tubes (8,
9),
a guide tube (10) for guiding the gas tube; and
a plurality of spokes (5) to provide strength to the spoked wheel
(4) and welded with the wheel (4) and the guide tube (10).

2. The system as claimed in claim 1, wherein an inert gas atmosphere
in vicinity of root pipe is generated.
3. The system as claimed in claim 1, wherein the inert gas directly
impinges on the root of the weld in a uniform manner by
perforated gas exodus.
4. The system as claimed in claim 1, wherein the inert gas enters into
the perforated gas exodus through the internal tube.
5. The system as claimed in claim 1, wherein the Spokes are welded
at its inner periphery to provide strength to the system.

ABSTRACT

The invention relates to an improved system for gas purging in pipes and tubes
comprising a gas exodus (1) for providing purging gas forward and trailing a
welding arc, a tube assembly (2, 3) welded to the exodus (1), the tube assembly
having an external tube (2) adjusting the gap between the exodus (1) and the
pipe to be welded, and an internal tube (3) having a gas hose pipe, a first and a
second telescopic tube (8, 9) having at a first side respectively external and
internal threads, the first telescopic tube (8) at a second side bearing a spherical
wheel (6) and a U-bend (7); spoked wheel (4) providing inertia of rotation to
the system and threadly connected with the first and second telescopic tubes (8,
9), a guide tube (10) for guiding the gas tube; and a plurality of spokes (5) to
provide strength to the spoked wheel (4) and welded with the wheel (4) and the
guide tube (10).