FIELD OF INVENTION:-
The invention relates to the process for Orbital TIG welding of boiler tubes of
grade SA 213 T 11 using deep penetration flux for applications in the pressure
parts of boiler/steam generators, which serve the purpose of effective heat
transfer in the equipment. More particularly, the invention relates to a process
for the orbital TIG welding of tube-to-tube cir-seam joint with square butt joint
edge preparation.
BACKGROUND OF THE INVENTION:-
Manufacturing of thermal power boilers involves thousands of tube-to-tube
welded joints. These tubes form a large part of the pressure parts of the power
boilers. Orbital TIG welding process is used particularly to join the tubular joints,
which cannot be rotated. In the prior art, J groove edge preparation is employed
for the orbital welding of tube butt joints. The TIG process has the advantage of
controlled heat input and clean weld due to the absence of flux. The weld is free
of spatter under the protection of a shielding gas, which at the same time
provides protection against harmful atmospheric contamination of the weld. The

process is distinguished by high quality weld and a low frequency of defects.
However, it has the limitation of low deposition rate. This means that hitherto
welding always had to be carried out in five passes during the welding of the
boiler tube walls, for the quality requirements call for substantial through welding
between tube to tube joint.
In the orbital tube welding system, the welding head rotates around the job
while the parts to be joined remain fixed. Since it requires a number of weld
passes to complete the joint, it necessitates a relatively high proportion of
handling and welding time in the entire fabrication process. This affects the
productivity and production in the shop floor. The arc time per weldment is high.
Besides, the filler wire, shielding gases and power consumption are also high.
In this regard, the process of Orbital TIG welding of boiler tubes of grade SA 213
Til using deep penetration flux in accordance with the invention overcomes the
limitations of the conventional orbital TIG welding method.
PRIOR ART:-
Patent NO US 3621177:
The patent discloses weld joining of metal tubing and more particularly concern a
novel method and apparatus for automatic fusion joining of abutting lengths of
tubing by means of an electric arc using a non-consumable electrode in an inert
atmosphere. Moreover this method is for using in process and nuclear

industries. This method also uses a purging flow of inert gas prior to the arc or
electrode rotation and calls for two complete welding cycles, terminating with a
bead cooling gas flow. The patent is not related to present invention at all.
PATENT NO. US 4009360
This patent deals about the construction of an orbital welding apparatus for
GTAW (TIG) and GMAW (MIG) processes. This patent is therefore also not
relevant to present invention.
PATENT NO. US 4142085
The patent for the method for tube joining is for root welding of a grooved joint
with a continuous wire in a gas shielded process having 0-40% CO2 and balance
argon. The joint is a beveled angle joint and balance weld is completed by
shielded metal arc welding. Thus it is different from the present invention.
OBJECTS OF THE INVENTION:-
It is therefore an object of the invention to provide a process for welding of
SA 213 T11 boiler tube to tube butt joint edge preparation.
Another object of the invention is to provide a process for welding of SA 213 T
11 boiler tube to tube in single pass, which is manifold productive.
A further object of the invention is to provide a process for welding of SA 213 T
11 boiler tube to tube which can do throughout the thickness without distortion
and other quality problems.

These and other objects and advantages of the invention will be apparent from
the ensuing description.
At the outset of the description, which follows, it is to be understood that the
ensuing description only illustrates a particular form of this invention. However,
such a particular form is only an exemplary embodiment and the teachings of the
invention are not intended to be taken restrictively.
SUMMARY OF THE INVENTION:-
Accordingly, there is provided a process for welding of SA 213 Til boiler tube to
tube which enables the joining of tube to tube which is achieved in single pass
welding by applying a deep penetration flux.
The square edge prepared tubes are fitted in the clamps with zero gap. After
ensuring right fit up of the joint, the orbital deep penetration flux is applied on
the joint area. Suitable welding parameters are set appropriate to the wall
thickness so that full penetration can be obtained in a single pass. The weld is
carried out by keeping the tubes stationary and the welding head rotates around
the job to complete the joint.
The technology developed is suitable for orbital TIG welding of fixed position
tube butt joints as well as rotating tube butt joints. The technological parameters
for achieving full penetration welds in single pass have been established for a
range of wall thickness (3 to 10mm) and diameter (30 to 100). The optimum

welding parameters, which give best results in terms of penetration, bead shape
and mechanical properties, have been established for different wall thickness of
the tubes to be welded.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:-
Fig.l shows the profile of the J groove joint of prior art.
Fig.2 shows an embodiment of the process according to the invention.
The invention will now be described in detail with the help of the accompanying
drawings.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION:-
The tubes (1) to be joined are taken up and the joining surfaces are cleaned to
remove oxide films, oil coating, etc. The cleaned edges are prepared to have a
square butt joint, so that the tubes can be fitted properly in the joint area. In the
prior art, a J groove in each tube was to be made as shown in fig.l and this
necessitates a separate facility and man power to do the operation. Now, there is
no need for a groove preparation. The square edge prepared tubes are fitted in
the clamps with zero gap. Standard orbital TIG welding head can be employed
for orbital TIG welding of tubes employing deep penetration flux. To produce the
SA 213 T 11 tube to tube joint, two tubes(l) are edge prepared for square butt
joint. The tubes are fit together without root gap. Then the deep penetration flux

(2) is sprayed/ applied by brush on the area to be jointed, uniformly. Then, the
welding is started with filler wire and weld is completed in a single pass.
After ensuring right fit up of the joint, the orbital deep penetration flux(2) is
applied on the joint area by using an aerosol can or by a brush or any other
mode. After applying the flux on the joint area, the welding parameters such as
type of shielding gas (argon/helium), welding current, welding voltage, welding
speed, wire feed rate, gas flow rate, torch angle, torch position and polarity are
selected on pendant(6), the parameters being appropriate for the wall thickness
of the tubes(l) being joined, so that full penetration can be obtained in a single
pass.
The weld is carried out by keeping the tubes stationary and the welding head (3)
rotates around the joint to complete the weld. The advantages of the invention
can be seen, inter alia, in the fact that the SA 213 T 11 boiler tube can be
welded in a single operation by employing orbital TIG welding using deep
penetration flux instead of five passes in prior art orbital TIG with J groove edge
preparation. The technology developed is suitable for orbital TIG welding of fixed
position tube butt joints as well as rotating tube joints. The technological
parameters for achieving full penetration welds in single pass have been
established for a range of wall thickness (3 to 10 mm) and diameter (30 to 100
mm). The head rotation speed, pulse current and wire feed speed has significant
influence on the weld penetration. The optimum process parameters, which give

best results in terms of penetration, bead shape and mechanical properties, have
been established. The welding is carried out with a weld speed in the range of
65-100mm/min.
The welded joint shown in Fig.2 is to be made with the least possible outlay by
the process according to the invention. For the fabrication of tube-to-tube joints,
the tubes have to be welded without any defect.
As shown in Fig.2, the tube edges are matched after machining and fixed in the
apparatus. The parameters for welding are set in the pendant of the machine.
Feeding the filler wire (5) in the weld pool starts the welding and the weld is
completed in single pas. The process in accordance with the invention produces
full penetration weld joints meeting radiographic quality for applications in
pressure parts of boilers, as per ASME sec IX and IBR regulations.

We Claim:-
1. A process for orbital TIG welding of boiler tubes of grade SA 213 T 11
comprising the steps of:
- cleaning of the joining surfaces of the tubes(l) to remove oxide films, oil
coatings etc;
- preparing the cleaned edges to have a square butt joint by machining;
- fitting the tubes (1) to be joined properly at the joint area with zero gap;
- applying deep penetration flux (2) on the joint area;
- holding the tubes (1) to be joined in fixed position through clamps;
- selecting a plurality of welding parameters on pendant (6) and
- welding the tubes,
characterized in that the welding is carried out by keeping the tubes stationary
and rotating the welding head (3) around the joint to complete the weld, and in
that the welding is carried out in a single pass with full penetration.
2. A process for TIG welding as claimed in claim 1, wherein the tubes (1) to be
joined have wall thickness lying between 3 and 10mm and internal diameter
lying between 30 and 100mm.

3. A process for TIG welding as claimed in claim 1, wherein said welding
parameters are type of shielding gas, welding current, welding voltage, welding
speed, wire feed rate, gas flow rate, torch angle, torch position and polarity.
4. A process for TIG welding as claimed in claim 1, wherein the welding
parameters are optimized for different wall thickness of the said tubes to be
welded.
5. A process for TIG welding as claimed in claims 1 and 3, wherein the welding
speed is between 65 and 100mm/min.
6. A process for TIG welding as claimed in claims 1 to 5, which produces full
penetration weld joints meeting radiographic quality as per ASME Sec. IX and
IBR regulations.
7. A process for TIG welding as claimed in claim 3, wherein the shielding gas is
either Argon or Helium.

A process for orbital TIG welding of boiler tubes of grade SA 213 T11 comprising the steps of:
- cleaning of the joining surfaces of the tubes(1) to remove oxide films, oil coatings etc;
- preparing the cleaned edges to have a square butt joint by machining;
- fitting the tubes (1) to be joined properly at the joint area with zero gap;
- applying deep penetration flux (2) on the joint area;
- holding the tubes (1) to be joined in fixed position through clamps;
- selecting a plurality of welding parameters on pendant (6) and
- welding the tubes.
The welding is carried out by keeping the tubes stationary and rotating the welding head (3) around the joint to complete the weld, and is completed in a single pass with full penetration.