Orbital welding system for welding tube joints in heat exchanger tubesheets

Abstract

A spherical welding system (1) for welding joints of tubes (2) of a tube sheet (3) of a heat exchanger includes a program-controlled generator (4), a spherical welding head (5), and a first supply line (6) of inert gas for TIG welding, the spherical welding head (5) including a welding torch (7), a stop system (8) for the torch (7) in contact with the tube sheet (3), an extendable centering tool (9) for fixing the spherical welding head (5) on one of the tubes (2), an actuator (10) for the centering tool (9), and a second supply line (11) for pressurized gas for operating the actuator (10), wherein in the spherical welding system (1), the second supply line (11) for pressurized gas branches off at a single point from the first supply line (6) and carries the same inert gas.

Description

[Technical Field]

[0001] The present invention relates to the field of mechanical engineering.

[0002] More particularly, the present invention relates to a spherical welding system for welding tube joints in a tubesheet of a heat exchanger.

[0003] A fairly important area in which spherical welding is used is in the field of heat exchangers with perforated tubesheets, where it is necessary to weld tube bundles of materials that can range from carbon steel to stainless steel, nickel alloys, and titanium, when maximum corrosion resistance is required.

[0004] In the spherical welding process, the welding torch is mechanically rotated 360° around the tube and then rotated again in a continuous process.

[0005] In most cases, tubesheet spherical welding is performed using TIG (tungsten inert gas) techniques using non-consumable tungsten welding rods, with or without filler wire if required. [Background technology]

[0006] Many factors can affect the welding results, including arc length, frequency and amplitude of current pulsation, feed rate, shielding gas, source material type, filler material, joint preparation, thermal conductivity, etc.

[0007] Achieving high levels of quality and safety in manual welding is extremely difficult. This is especially true due to welding positions such as vertically downward, overhead, and vertically upward, which can clearly result in defective welds due to gravity and the difficulty of movement posed to the operator in these positions. If complete control over the weld pool is desired, a perfect balance is required between the effects of gravity and the surface tension at any position of the torch. Using mechanical equipment, these properly and automatically manage the welding process, despite the fact that the operator must constantly monitor and control the progress of the cycle. In an ideal situation, all parameters should be fully programmed before welding begins. In automatic welding, the welding process is performed completely independently and programmably, without the need for operator intervention.

[0008] The main components of an automated TIG spherical tube welding system are a generator with programming control, a spherical welding head, a cooling system, an inert gas supply line to protect the weld, and, if required, a filler wire feeder.

[0009] The gas typically used is argon or a mixture of argon with limited proportions of helium or hydrogen.

[0010] The welding head substantially includes an electrode holder torch, a stop system for the torch contacting the tubesheet, an extendable centering tool for locking the welding torch on one of the tubes, an actuator for activating the centering tool, and a second pressurized air supply line for operating the actuator.

[0011] An actuator with a welding torch, an extendable centering tool, and a compressed air supply line is mounted to the rotary joint.

[0012] A known type of centering tool comprises an axial rod on which two resilient locking grippers are mounted opposite each other, which expand radially inside the tube to be processed and thereby cooperate with a stop system to lock the welding head in contact with the tubesheet.

[0013] Each gripper is deformed as a result of inserting an expander cone that is retracted by the rod of the centering tool.

[0014] An actuator for controlling the centering tool acts on the rod, pulling it and thus inserting the expander cone into the elastic gripper, the actuator including a single pneumatically actuated piston supplied by a compressed air circuit.

[0015] Such spherical welding systems have several limitations and drawbacks.

[0016] The main drawback is the use of compressed air to control the centering tool actuator.

[0017] To operate the centering tool, the compressed air used must have a minimum pressure of 6-7 bar. Bringing compressed air at such pressure into the rotary joint of the welding head involves the risk of any leaks (even the smallest) in the gasket of the joint itself. It also contaminates the inert gas dedicated to protecting the weld, which is always released at a significantly lower pressure of about 0.5 bar. Compressed air contaminates the working environment of the torch and can cause unwanted spray and pitting in the weld.

[0018] Additionally, compressed air supply lines have a large footprint at the weld head and require connection and disconnection to circuits external to the welding system, creating logistical constraints.

[0019] Also, known centering tools required to lock the weld head to the tubesheet also have drawbacks.

[0020] Unfortunately, the two elastic grippers are activated by a single actuator, but they cannot expand simultaneously. The opening of the two grippers does not occur simultaneously. One of the grippers, in cooperation with its corresponding expander cone, will expand before the other gripper, and tool centering of the tube will not be guaranteed.

[0021] Furthermore, there is no means to release the cone from the gripper when the operation is finished, and the centering tool must be extracted, the normal extraction movement of which always involves exerting a small pulling force on the rod, which runs the risk of extending the gripper again.

[0022] Because a single actuator is used to act on two grippers, the expansion that can be achieved is limited, and as a result, different centering tools with different diameters are required to cover all possible dimensions of the tube, resulting in economic disadvantages regarding the overall cost of the system. Summary of the Invention [Problem to be solved by the invention]

[0023] The object of the present invention is to overcome these limitations by defining an efficient, totally automated and easy to maintain spherical welding system for welding tube joints in heat exchanger tube sheets that ensures precision welds.

[0024] It is also an object of the present invention to provide a freestanding welding head that ensures stability and centering of the torch without manual intervention by the operator and that can be easily moved from an already welded pipe to a new pipe to be welded by withdrawing and reinserting the centering tool. [Means for solving the problem]

[0025] Such an object is realized by a spherical welding system for welding tube joints in tube sheets of heat exchangers, - a programmable generator; a spherical welding head; a first supply line of inert gas for TIG welding, The spherical welding head is -A welding torch, a stop system for said torch in contact with the tubesheet; an expandable centering tool for securing the spherical welding head on one of the tubes; an actuator for said centering tool; a second supply line for pressurized gas to operate said actuator; The spherical welding system is characterized in that the second supply line for pressurized gas branches off from the first supply line at one point and carries the same inert gas.

[0026] According to the first aspect of the present invention, the second supply line includes a pressure boosting device provided at the branch point.

[0027] Additionally, the first supply line includes a pressure reducing device.

[0028] In a preferred variant of the invention, the second supply line includes an air valve that manages the passage of gas in the actuator to actuate the expandable centering tool.

[0029] Advantageously, the air valve is of the three-way type, allowing the release of gas from the actuator and the attachment and detachment of the expandable centering tool from the tube.

[0030] According to a preferred embodiment of the present invention, the expandable centering tool comprises: a radial guide cartridge provided with balls; an elastic shaft locking gripper; a pull rod associated with said actuator, with which said guide cartridge and said resilient gripper are rotatably associated; Includes.

[0031] Advantageously, a thrust bearing is interposed between said guide cartridge and said resilient gripper.

[0032] Specifically, the centering tool comprises: a thrust head integral with said traction rod; an expander cone adapted to act on said elastic gripper by virtue of said thrust head against the elastic action of a helical release spring; a thrust bearing interposed between the thrust head and the expander cone; Includes.

[0033] According to a further aspect of the invention, the actuator includes a piston and an eccentric control lever, a first end of the eccentric control lever coupled to the piston and a second end of the eccentric control lever coupled to the pull rod of the centering tool.

[0034] Preferably, the actuator includes a reversible restraining means disposed between the second end of the eccentric control lever and the tow rod. [Effects of the Invention]

[0035] The present invention provides several advantages, which are described below.

[0036] A major advantage of the present invention arises from the use of the same inert gas already used to protect the weld and also to activate the centering tool.

[0037] The gas supply line to the actuator branches off from the inert gas supply line to the welding torch, advantageously thus reducing the overall size of the system and eliminating the need to connect to other external compressed air lines.

[0038] The elimination of compressed air reduces the risk of blowout and accidental perforations in the weld, because even if there are gas leaks from the actuator and in the vicinity of the welding rod, these leaks will run out of air under pressure, but the inert gas itself will always stabilize the weld.

[0039] The resulting weld is therefore more precise and free of defects and burrs, with significantly less risk of weld sagging and no sink marks in the tube hole that can make it difficult to extract the centering tool.

[0040] The pressure intensifier device installed in the second gas supply line allows the actuator to reach the optimum operating pressure (maximum 7-8 bar). Vice versa, the demultiplier device installed in the first gas supply line to the welding torch allows the gas pressure to be reduced to a maximum of 0.5 bar, i.e., the recommended value for a successful full weld without waste and consumption.

[0041] The centering tool according to the invention acts on two front sides: the guide cartridge with spring-loaded balls acts radially and ensures the positioning of the tool relative to the tube in the axis, while the elastic gripper with extensions blocks the tool longitudinally and allows the fixing of the spherical welding head relative to the tube sheet of the tube to be welded.

[0042] Additionally, the operator is not required to support the spherical head during welding: the spherical head remains fixed to the tubesheet by the centering tool.

[0043] The centering tool according to the invention therefore ensures centering and stability for the spherical head during the welding step, while at the same time ensuring easy and accurate extraction of the tool itself from the tube after welding.

[0044] In fact, the helical release spring of the expander cone facilitates the return of the resilient gripper to its rest configuration, facilitating the extraction of the centering tool from the tube without the risk of the gripper itself remaining partially engaged by the expander cone.

[0045] Unlike the prior art, the actuator only needs to act with a single elastic gripper, and the same force and pulling stroke applied by the actuator results in a larger gripper extension. In addition to making it possible to use a single centering tool for pipes with a wide range of diameters, the ability to reach a larger gripper extension allows the centering tool to maintain a reduced diameter, thus facilitating its extraction from the pipe even in the case of a slight overflow of the weld due to partial blockage of the pipe mouth.

[0046] The reversible restraint between the actuator lever and the towing rod of the centering tool facilitates maintenance operations on the welding head, but even more advantageously, facilitates extraction of the centering tool in the event of partial blockage of the tube mouth again due to weld overflow. In fact, it is sufficient to act on such a reversible restraint to release and remove the spherical welding head and all its accessories, the included actuator, from the tubesheet, leaving only the centering tool inside the tube, as well as the space required for the operator to operate and remove the tool.

[0047] The advantages of the invention will appear more clearly from the following description of preferred embodiments, given by way of indicative and non-limiting example, with reference to the drawings. [Brief explanation of the drawings]

[0048] [Figure 1] 1 shows an axonometric view of the main components of a spherical welding system for welding tube joints in a tube sheet of a heat exchanger according to the present invention. [Figure 2] 2 shows a schematic diagram of a portion of the system of FIG. 1; [Figure 3] 2 illustrates a partial cross-sectional side view of components of the welding system of FIG. 1 in operation. [Figure 4] 3 shows a cross-sectional view of components of a system according to the invention in a stopping step; [Figure 5] 1 shows a longitudinal section of the components of a system according to the invention in a stopping step; [Figure 6] 1 shows cross-sectional views of components of a system according to the invention in different working steps; [Figure 7] 1 shows longitudinal sections of components of a system according to the invention in different working steps; DETAILED DESCRIPTION OF THE INVENTION

[0049] 1 and 2, there is shown a spherical welding system 1 using TIG technology for welding joints of tubes 2 in a tubesheet 3 of a heat exchanger.

[0050] The spherical welding system 1 essentially comprises: - a programmable generator 4; a spherical welding head 5; a first supply line 6 of inert gas for TIG welding; Includes.

[0051] The first supply line 6 usually branches off in the immediate vicinity of the cylinder, and the gas pressure inside the first supply line 6 is generally 2.4 to 4 bar.

[0052] The spherical welding head 5, which is clearly visible in the detail of FIG. -Welding torch 7, a tip stop system 8 for said torch 7 in contact with the tubesheet 3; an extendable centering tool 9 for welding the spherical welding torch 7 on one of the tubes 2; Includes.

[0053] The centering tool 9 allows stable fixing of the spherical welding head 5 to the tube sheet 3 without the contribution of the operator. The spherical welding head 5 alone can be suspended on a cable for greater safety during extraction and positioning operations.

[0054] The spherical welding head 5, in turn, includes an actuator 10 for the centering tool 9. The actuator 10 includes a single pneumatically operated piston 14, and the spherical welding head 5 includes a second line 11 for supplying pressurized gas to operate the actuator 10.

[0055] Advantageously, the inert gas used as protective gas for welding is the same gas used to operate the actuator 10, and the supply line for that gas or the second line 11 branches off in the immediate vicinity of the first main supply line 6 which carries the inert gas in close proximity to the welding rod of the torch 7.

[0056] The point where argon is taken to feed from said first line 6 to said second feed line 11 is called the branch point.

[0057] At the branch point, the second supply line 11 contains a pressure boosting device 12 necessary to bring the gas pressure in the first line 6 to a value between 5 and 8 bar.

[0058] The second supply line 11 includes an air valve 14 that manages the passage of gas to the actuator 10 to actuate the expandable centering tool 9. The air valve 14 includes a manual switch 26 that, when engaged, allows the operator to directly decide to activate or deactivate the expansion of the centering tool 9 inside the tube 2.

[0059] The air valve 14 is installed along the second supply line 11 adjacent the orb welding head 5 to minimize the response time of the actuator 10 and limit consumption of gas under pressure.

[0060] The air valve 14 is of the three-way type and also makes it possible to release to the atmosphere any residual gas present in the actuator 10 when the elastic gripper 17 is inactive and the centering tool 9 is disengaged from the tube 2.

[0061] Along said first supply line 6, on the other hand, a pressure reducing device 13 is suitably arranged to reduce the pressure of the argon gas from a value of 2.4-4 bar to a value of about 0.5 bar, or to the optimum pressure value at which the gas needs to act to protect the weld.

[0062] With particular reference to FIGS. 4 to 7, the expandable centering tool 9 comprises: a guide cartridge 15 provided with a spring-loaded ball 16; - an elastic shaft locking gripper 17 that acts by expanding; a tow rod 18 associated with the actuator 10 at one of its ends 18', with which both the guide cartridge 15 and the elastic gripper 17 are rotatably associated; Includes.

[0063] The guide cartridge 15 contains a number of floating balls 16 which are free to move radially and whose projections change relative to the outer diameter of the guide cartridge 15, and thus the diameter of the centering tool 9. The movement of the balls 16 occurs in cooperation with a helical spring 27 inside the guide cartridge 15.

[0064] The resilient gripper 17 comprises an axially bored cylinder 28 into which the towing rod 18 is inserted. The cylinder 28 is provided with a longitudinal cut 29 which forms a flexible compliant arm 30. The free end of the flexible arm 30 is shaped and includes an internal bevel 31 and an external jaw 32. When the resilient gripper 17 expands, the free end cooperates with the inner surface of the tube 2.

[0065] The draw rod 18 includes a thrust head 20 at a second end 18 ″ opposite end 18 ′ for restraint to the actuator 10 provided by a nut 33 and a lock nut 34 .

[0066] A thrust bearing 19 is interposed between the guide cartridge 15 and the elastic gripper 17 so that they each rotate independently around the towing rod 18. In use, when the centering tool 9 is in fact active inside the tube 2 to be welded, the ball guide cartridge 15 rotates freely with the towing rod 18 (except to compensate for any friction with the rotation of the balls 16), while the elastic gripper 17 is in an extended position and its outer jaw 32 is blocked against the inner surface of the tube 2 (instead, the towing rod 18 rotates freely inside the cylinder 28 of the elastic gripper 17).

[0067] The centering tool 9 includes an expander cone 21 for the elastic gripper 17 .

[0068] The expander cone 21 is adapted to act on the elastic gripper 17 by virtue of the thrust head 20 against the elastic action of a helical ejection spring 22, which is mounted together with the elastic gripper 17 inside a cylinder 28 and wound around the pulling rod 18.

[0069] Referring to the section of Figure 7, the gradual insertion of said expander cone 21 inside the flexible arm 30 of the gripper 17 is favoured by the cooperation of the inclined surface 31 with the cone of the expander cone 21, resulting in the expansion of the gripper itself and of the outer jaws 32 which fix on the inner surface of the tube 2.

[0070] The thrust bearing 23 is interposed between the head thrust bearing 20 and the expander cone 21 to eliminate possible friction, as the thrust head 20 and towing rod 18 are free to rotate axially with the tube 2 during welding against a resilient gripper 17 engaged by an expander cone 21 which remains fixed and locked in the expanded position.

[0071] The manner in which the actuator 10 is coupled to the towing rod 18 of the centering tool 9 offers particular advantages.

[0072] The actuator 10 includes a piston 24 and an eccentric control lever 25, a first end 25' of the eccentric control lever 25 being associated with the piston 24 and a second end 25'' of the eccentric control lever 25 being associated with the pull rod 18 of the centering tool 9.

[0073] The second end 25 ″ of the eccentric control lever 25 is U-shaped and engages the end 18 ′ of the draw rod 18 and is held against extraction by a stop surface 35 .

[0074] Advantageously, the actuator 10 includes reversible restraining means arranged between the second end 25" of the eccentric control lever 25 and the end 18' of the towing rod 18. In the variant shown, the reversible restraining means is represented by a nut 36 threaded onto the towing rod 18. The nut 36 forms a stop surface 35 against extraction of the second end 25" of the eccentric control lever 25.

[0075] The possibility of easily releasing the centering tool 9 from the actuator 10 and thus from the main block of the spherical welding head 5 is particularly advantageous when conditions of excessive overflow of the weld occur, for example limiting the outlet diameter of the tube 2 to a value smaller than the minimum diameter of the centering tool 9 when not expanded.

[0076] When this situation occurs, the solution for the purposes of the present invention allows the centering tool 9 to be removed from the actuator 10 by unscrewing the rear nut 36 of the tow rod 18 with a simple tool, once the welding torch 7 is clear of the tubesheet 3. Once the entire spherical welding head 5 is removed from the tubesheet 3, only the centering tool 9 remains inside the tube 2, and the centering tool 9 can be pushed out at the opposite end of the tube, or the weld overflow can be extracted immediately after cutting. In both cases, the centering tool 9 remains undamaged and can be reassembled with the spherical welding head 5 for later use.

Claims

1. An orbicular welding system (1) for welding joints of tubes (2) of a tube sheet (3) of a heat exchanger, comprising: - a program-controlled generator (4), - an annular welding head (5), a first supply line (6) of inert gas for TIG welding, The annular welding head (5) - a welding torch (7), - a stop system (8) for said torch (7) in contact with the tube sheet (3); - an expandable centering tool (9) for fixing said annular welding head (5) on one of said tubes (2); - an actuator (10) for said centering tool (9); a second supply line (11) for pressurized gas to operate said actuator (10), 1. The annular welding system (1), characterized in that the second supply line (11) for pressurized gas branches off from the first supply line (6) at one point and carries the same inert gas.

2. 2. An orbital welding system (1) according to claim 1, characterized in that the second supply line (11) includes a pressure booster device (12) provided at a branch point.

3. 2. An orbital welding system (1) according to claim 1, characterized in that the first supply line (6) comprises a pressure reducing device (13).

4. 2. The orbicular welding system (1) according to claim 1, characterized in that the second supply line (11) includes a valve (14) that controls the passage of gas through the actuator (10) for operating the expandable centering tool (9) and is actuated by the pressure of the gas.

5. 5. The orbicular welding system (1) according to claim 4, characterized in that the valve (14) is of the three-way valve type and allows gas release from the actuator (10) and attachment and detachment of the expandable centering tool (9) to and from the tube (2).

6. The expandable centering tool (9) - a radial guide cartridge (15) provided with balls (16), - an elastic shaft locking gripper (17), a tow rod (18) associated with said actuator (10), with which said guide cartridge (15) and elastic gripper (17) are rotatably associated; An orbicular welding system (1) according to claim 1, characterized in that it comprises:

7. 7. An orbicular welding system (1) according to claim 6, characterized in that a thrust bearing (19) is interposed between the guide cartridge (15) and the elastic gripper (17).

8. The expandable centering tool (9) a thrust head (20) integral with said traction rod (18); an expander cone (21) adapted to act on said elastic gripper (17) by virtue of said thrust head (20) against the elastic action of a helical ejection spring (22); a thrust bearing (23) interposed between the thrust head (20) and the expander cone (21); An orbicular welding system (1) according to claim 6, characterized in that it comprises

9. 7. The orbital welding system (1) according to claim 6, characterized in that the actuator (10) comprises a piston (24) and an eccentric control lever (25), a first end (25′) of the eccentric control lever (25) being coupled to the piston (24) and a second end (25″) of the eccentric control lever (25) being coupled to the tow rod (18) of the centering tool (9).

10. 10. The orbital welding system (1) according to claim 9, characterized in that the actuator (10) includes a reversible restraining means arranged between the second end (25″) of the eccentric control lever (25) and the tow rod (18).

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