FIELD OF THE INVENTION
The present disclosure relates to butt welding of tubes, more particularly towards automatic pre-heating of tubes prior to butt welding.
BACKGROUND OF THE INVENTION
Steam generators used for power generation have several heat absorbing components like super heaters, re-heaters, economisers & water wall panels. Most of the tube raw materials are supplied in length of 10 m by domestic as well as foreign tube suppliers. In re-heater, economiser, and super heater coils have design requirement up to 40m length. So, in order to get increase length of tubes, “tube to tube butt welding machine” simply known as Straight Tube Butt Welding Machine (STBW) is used.
Several material grades are used in Boiler tubing, for example carbon steel (Grade A1, Grade C), lower alloy steel (T11, T12 & T22), Higher alloy steel (T23, T91, T92), and Stainless steel (347H, Super 304H). Except carbon steel, all other grades of material require preheating to pre-determined temperature to avoid brittleness of the alloy steel materials. For this, conventional heating torch is used with Liquid Petroleum Gas (LPG) and the operators have to hold the pre-heating torch in position with flame while the uniform rotation of the tubes fixed on the chucks of the welding machine. Based on the experience of the operator, the flame is switched off after

some duration and a thermo chalk is used to check the desired temperature. The process is repeated as above till the desired temperature is obtained.
In the above process, one operator has to be necessarily engaged to hold the pre-heating torch till the desired pre-heating temperature is not achieved. More over certain time is taken to check the desire surface temperature with thermo chalk. Such is a tedious and time-consuming process, considering large number of joints, for example 40 for a single super heater coil assembly / re-heater coil assembly, and the number of assembly required per steam generators, for example 10. More over if Induction pressure heating is employed, the coil has to be dismantled before welding starts, which is again a time-consuming process. Hence it is imperative to find an alternative method of pre-heating with elimination of manpower and to increase the productivity of the process.
OBJECTS OF THE INVENTION
An object of the invention is to provide an apparatus, a process, or a system including components like solenoid valves, PLC (Programme Logic Control) controller for automotive pre-heating of tubes by overcoming the deficiencies and disadvantages of the prior art.

Another object of the invention is to eliminate the manual involvement during pre-heating of tubes.
SUMMARY OF THE INVENTION
The present disclosure relates to an automatic system (100) for pre-heating of tubes (9) prior to butt welding in a Straight Tube Butt welding (SBTW) machine. The system (100) includes a welding torch (1) for performing a welding operation; a clamp (2), proximal to the welding torch (1), for securing a preheating torch (3), the preheating torch (3) is configured for performing a preheating operation; a programme logic control (PLC) (4) coupled with the welding torch (1) and the preheating torch (3), the PLC (4) includes a plurality of switches (5, 6, 7); and a chuck (8), proximal to the preheating torch (3), for receiving tubes (9), the tubes (9) are clamped in the chuck (8) and are butt together, wherein the tubes (9) are preheated by the preheating operation, and subsequently welded by the welding operation, the preheating operation and the welding operation being controlled by the PLC (4).
The present disclosure also relates to a method for automatic pre-heating of tubes (9) prior to butt welding in a Straight Tube Butt welding (SBTW) machine. The method includes providing tubes (9) in chuck (8) of the machine; positioning a welding torch (1) and a preheating torch (3) proximal to the tubes (9) for performing a welding operation and a preheating

operation respectively, the welding operation being performed subsequent to the preheating operation; supplying, controlled by a PLC (4), LPG gas to the preheating torch (3); igniting, controlled by the PLC (4), the LPG gas to start the preheating operation; shutting off, controlled by the PLC (4), the LPG gas and the igniting, based on completion of the preheating operation; and starting, controlled by the PLC (4), the welding operation to weld the tubes (9).
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings of the exemplary embodiments and wherein:
Figure 1 shows: Schematic diagram of the “Automatic system for pre-
heating of alloy tubes prior to butt welding”.
Figure 2 shows: Schematic diagram of a holding clamp used for holding
preheating torch in the welding torch housing unit of the Automatic system of Figure 1.

6
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
The present invention, now be described more specifically with reference to the following specification.
Figure 1 illustrates an Automatic system 100 for pre-heating of alloy tubes (9) prior to butt welding in accordance with an embodiment of the present disclosure. The
system 100 includes the following components:

Part No. Component
1 Welding torch
2 Clamp
3 Conventional torch
4 PLC
5 Switch
6 Switch
7 Switch
8 Chuck
9 Tubes
10 LPG hose
11 LPG cylinder
12 Spark Plug
13 Solenoid valve
14 Cable
15 Housing unit
16 Servo motor
17 Gas Regulator

Figure 2 illustrates a schematic diagram of the holding clamp (2) used for holding the conventional preheating torch (3) in the welding torch housing unit (15). As shown, the clamp (2) includes two halves (21, 22), wherein each half of the halves defines an annular region (23, 24). In an embodiment, the two halves (21, 22) are configured to be secured to each other through a plurality of screws (25), such that the annular region (23, 24) in combination define a receptacle for receiving the torch (3).
Operation of the automatic system 100 employing the aforementioned components will now be described in the foregoing description. The system 100 is configured for automation of the pre-heating in a Straight Tube Butt welding (SBTW) machine. As shown, two tubes (9) configured to be welded, are clamped in chuck (8), and made butt together. The tubes (9) to be welded and preheated are loaded on the welding machine stand or rack. Then by a tube feeding system tubes (9) are passed between two chucks (8) provided in the machine. By using a stopper provided between the chucks (8), the tubes (9) are halted in correct position and the chucks (8) are clamped to hold the tubes (9).
The system 100 includes a welding torch (1) for welding the tubes (9). In an embodiment, before welding, the tubes (9) are preheated by a conventional preheating torch (3) fixed or clamped by a clamp (2) in the SBTW machine torch housing unit (15). In the system 100, the preheating of the tubes (9) is done by burning of LPG gas from an LPG cylinder (11). The LPG cylinder (11)

is connected to the preheating torch (3) through LPG hose (10). The gas flow from the LPG cylinder (11) to the torch (3) is controlled by a solenoid valve (13). In an embodiment, the solenoid valve (13) is connected to a Programme Logic Control (PLC) (4) by means of a cable (14) to adjust flame of the torch (3). The preheating torch (3) is ignited by a spark plug (12). In an embodiment, the PLC (4) includes a switch (5) to control LPG Torch, switch (6) to control welding Torch, and switch (7) to control LPG Ignition . Further, preheating oscillation associated with the system 100 are controlled by a servo motor (16) through PLC (4). Thus, preheating of tubes (9) is done automatically through PLC (4) control, based upon gas flow through LPG cylinder (11) controlled by gas regulator (17).
The PLC (4) control system is configured for two programmes / operations, i.e. firstly preheating of the tubes (9), and then welding of the tubes (9). For preheating operation, burning of LPG gas from the LPG cylinders (11) is used. LPG gas pressure to be required in the system 100 is controlled by the LPG cylinder regulator (17). After calling the preheating operation on PLC (4) for preheating, the preheating torch (3) is positioned proximally to the tubes (9). Then the switch (7) is activated to actuate the solenoid valve (13) to enable flow of LPG gas through LPG preheating troch (3). After that, spark plug (12) is activated for igniting the LPG gas, and put preheating torch (3) in operation.

The tubes (9), clamped in the chuck (8), are also configured to rotate during the preheating, such that nearby edges to be weld are heated optimally by the preheating torch (3), the preheating torch (3) being oscillating 20 mm both sides from the centre of the tubes (9) joint meant to be welded. The oscillation of the preheating torch (3) is controlled by the PLC (4). After the tubes (9) attains sufficient temperature from preheating, the PLC (4) shuts and auto cut off the LPG gas supply. In an example, to calculate the sufficient temperature range optimal for the tubes (9), a sample job may be preheated first, and recorded parameters may be feed in the PLC (4) for performing the preheating operation. In a nutshell, the PLC (4) controls operation of the following components during preheating of the tubes (9) -preheating torch (3) oscillation, tubes (9) rotation, recording and controlling preheating time and temperature, solenoid valve (13) open and close to start and stop LPG gas supply, and spark plug (12) ON and OFF.
Once the preheating of the tubes (9) is completed, the welding operation is started by the PLC (4) to weld the joints that is fixed in the same frame (15) as shown in the figure-1. For super heater coils and re-heater coils the tubes (9) are welded up to the build-up length of 24 m to 72 meters, and also for various thickness of tube and various material specification (varying thickness from 4mm to 15mm).

Hence, in the system 100 described above, no operator has to be necessarily engaged to hold the pre-heating torch till the desired pre-heating temperature is achieved. Moreover, checking the desire surface temperature with thermo chalk is also avoided. Thus, the system 100 of pre-heating provides elimination of manpower, and increases productivity and efficiency of the process.
It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims.

WE CLAIM:
1. An automatic system (100) for pre-heating of tubes (9) prior to
butt welding in a Straight Tube Butt welding (SBTW) machine, the system (100) comprising:
a welding torch (1) for performing a welding operation;
a clamp (2), proximal to the welding torch (1), for securing a preheating torch (3), the preheating torch (3) is configured for performing a preheating operation;
a programme logic control (PLC) (4) coupled with the welding
torch (1) and the preheating torch (3), the PLC (4) includes a
plurality of switches (5, 6, 7); and
a chuck (8), proximal to the preheating torch (3), for receiving tubes (9), the tubes (9) are clamped in the chuck (8) and are butt together, wherein the tubes (9) are preheated by the preheating operation, and subsequently welded by the welding operation, the preheating operation and the welding operation being controlled by the PLC (4).
2. The automatic system (100) as claimed in claim 1, wherein the
preheating torch (3) is configured to receive LPG gas from an LPG hose (10) coupled to an LPG cylinder (11).

3. The automatic system (100) as claimed in claim 2, wherein a spark plug (12), controlled by the PLC (4), ignites the LPG gas to enable the preheating torch (3) to perform the preheating operation on the tubes (9).
4. The automatic system (100) as claimed in claim 2, wherein the LPG gas flow from the LPG cylinder (11) to the preheating torch
(3) is controlled by a solenoid valve (13), the solenoid valve (13) being operated by the PLC (4).
5. The automatic system (100) as claimed in claim 2, wherein a
pressure of the LPG gas flowing from the LPG cylinder (11) to the preheating torch (3) is controlled by a gas regulator (17), the gas regulator (17) being operated by the PLC (4).
6. The automatic system (100) as claimed in claim 1, wherein
preheating oscillation associated with the preheating torch (3) is
controlled by a servo motor (16) through PLC (4).

7. The automatic system (100) as claimed in claim 1, wherein the
chuck (8), and in turn the tubes (9), is configured to rotate during
the preheating operation.
8. A method for automatic pre-heating of tubes (9) prior to butt
welding in a Straight Tube Butt welding (SBTW) machine, the method
comprising:
providing tubes (9) in chuck (8) of the machine;
positioning a welding torch (1) and a preheating torch (3) proximal to the tubes (9) for performing a welding operation and a preheating operation respectively, the welding operation being performed subsequent to the preheating operation;
supplying, controlled by a PLC (4), LPG gas to the preheating torch (3);
igniting, controlled by the PLC (4), the LPG gas to start the preheating operation;
shutting off, controlled by the PLC (4), the LPG gas and the igniting, based on completion of the preheating operation; and
starting, controlled by the PLC (4), the welding operation to weld the tubes (9).

9. The method as claimed in claim 8, wherein the supplying of the LPG gas is from an LPG hose (10) coupled to an LPG cylinder (11).
10. The method as claimed in claim 8, wherein the PLC (4) controls:
the supplying through a pressure regulator (17) and solenoid valve (13),
the igniting through a spark plug (12), and
the shutting off through the spark plug (12) and the solenoid valve (13).