A welding process for argon arc welding of a surfacing pipe butt joint

Abstract

The present application prevents the problem of leaving a gap between two pipe sections in prior art and then performing manual surfacing after butt welding by adopting the mode of covering the whole pipe width with a surfacing layer before butt welding of the pipe, and adopts the mode of self-melting of base metal without adding wire to weld the backing layer weld, generates first-level protection to the pipe base metal through the formation of the backing layer weld consistent with the pipe base metal, and generates second-level protection to the pipe base metal through the filling layer weld by using the welding wire matched with the pipe base metal to weld the filling layer weld after welding the backing layer weld, and prevents the nickel-based alloy layer of the last surfacing from entering the backing layer weld.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of welding of serpentine pipes; in particular, it relates to a welding process for butt welding of a cladded pipe by argon arc welding. BACKGROUND

[0002] A serpentine pipe is a structure often used in the convection heating surface devices of a boiler, such as an economizer, a superheater and a reheater. The total length of a commonly used serpentine pipe is more than 30 meters, and the pipe is formed by welding multiple pipes together. In order to improve the overall efficiency and quality, the pipes are welded together by automatic argon arc welding, and then are automatically transported to a pipe bending device for bending into a serpentine pipe. Figure 1 Fig. 1 is a structural diagram of a serpentine pipe and a butt weld position diagram.

[0003] Since the economizer, the superheater and the reheater operate in a boiler, the ordinary carbon steel or alloy steel pipe is easily corroded by high-temperature corrosive gas, and the pipe wall is easily thinned to cause leakage. Therefore, it is a common practice to cladding the outer wall of the pipe with a corrosion-resistant nickel-based alloy.

[0004] When butt welding the cladded pipe, the base metal of the carbon steel or alloy steel pipe is welded using the corresponding carbon steel or alloy steel welding material. During welding, if the nickel-based alloy cladding layer enters the carbon steel or alloy steel weld, it will cause welding cracks and affect the welding quality. Therefore, the current mainstream solution is to leave about 30-50mm of the base metal at both ends of the cladded pipe during cladding, and after automatic butt welding and pipe bending are completed, the remaining base metal is covered with the nickel-based alloy by manual cladding. Figure 2 Fig. 2 is a schematic diagram of butt welding of two cladded pipes in the prior art. Figure 3 Fig. 3 is a specific process flow of butt welding of two pipes in the prior art.

[0005] As can be seen from the prior art, although the pipe cladding in the prior art is performed before butt welding of the two pipes, in order to prevent the nickel-based alloy cladding layer from entering the carbon steel and alloy steel weld, the automatic cladding cannot cover the entire pipe, and the butt joint surface needs to be left without welding. After the butt welding is completed, manual cladding is performed on the remaining gap, which first causes the process to be complex, i.e., the process of cladding-butt welding-cladding needs to be completed, and secondly, since the remaining gap of the pipe is too narrow, manual cladding can only be performed after the butt welding is completed, and the efficiency of manual cladding is very low, and manual cladding is very unstable, which can cause the nickel-based alloy cladding layer to be uneven. SUMMARY

[0006] In order to solve the above technical problems, the present application provides a process for automatic butt welding of a nickel-based alloy cladded pipe, which can ensure the welding quality of the automatic butt weld and the appearance of the weld without leaving a non-cladded pipe at the end of the cladded pipe.

[0007] A process for automatic butt welding of a nickel-based alloy clad pipe, comprising the following steps:

[0008] 1. Prepare the pipe according to the drawing.

[0009] 2. Clad the pipe; the clad layer covers the entire width of the pipe.

[0010] 3. Process the clad pipe according to the drawing; the end of the pipe should be flat and a 35° bevel with a root face of 0-0.5 mm should be processed.

[0011] 4. Use an automatic argon arc welding system for welding; the welding torch is located at the top of the pipe within a range of ±5°.

[0012] 4.1. Align the pipe through the automatic argon arc welding system to ensure a 0 gap.

[0013] 4.2. Use a non-wire, base material self-fusion method to weld the backing layer weld; the welding torch does not swing during the welding process. The backing layer weld should be 5-15 mm longer than the inner diameter of the pipe to ensure that the arc is collected and the starting point is offset.

[0014] 4.3. Use a welding wire that matches the base material of the pipe to weld the filler layer weld; the welding torch does not swing during the welding process; the number of layers is set according to the thickness of the base material, and through preliminary process testing, it is ensured that the backing layer weld is 0.5-1 mm below the surface of the base material to ensure that the nickel-based alloy metal of the clad layer does not invade the backing layer weld; the filler layer weld should be 5-15 mm longer than the inner diameter of the pipe to ensure that the arc is collected and the starting point is offset.

[0015] 4.4. Use a nickel-based alloy metal wire for cladding to weld the filler layer; the welding torch swings during welding and needs to be heated to above 300°C through resistance heating. According to the different thickness requirements of the cladding layer, the cladding filler layer weld is welded for more than one layer. The cladding filler layer and the cladding cover layer weld are continuously welded without stopping the arc between each layer. The cover layer weld should be 10-15 mm longer than the first layer of filler layer weld to ensure that the arc is collected and the starting point is offset.

[0016] 5. Perform RT non-destructive testing on the pipe.

[0017] 6. Bend the pipe.

[0018] 7. Proceed to the subsequent process.

[0019] The aforementioned surfacing process avoids the problem of leaving gaps between pipe sections for manual surfacing after butt welding by covering the entire width of the pipe before butt welding, as is common in existing technologies. Furthermore, it employs a self-fusion method with the base material without wire to weld the root pass, providing primary protection to the pipe base material through the formation of a root pass consistent with it. A secondary protection is provided by welding the filler pass with a wire matching the pipe base material after the root pass, preventing the final nickel-based alloy layer from entering the root pass. Even if the nickel-based alloy layer enters the filler pass during surfacing, it will not enter the root pass; even if welding process issues cause the nickel-based alloy layer to enter the root pass, it will not enter the pipe base. This secondary protection mechanism effectively protects the pipe base material, and the welding torch oscillation during nickel-based alloy layer surfacing prevents the nickel-based alloy weld layer from accumulating and entering the filler pass. Attached Figure Description

[0020] Appendix Figure 1 This is a schematic diagram of the serpentine tube structure.

[0021] Appendix Figure 2 This is a schematic diagram of butt welding of two pipes after overlay welding in the prior art.

[0022] Appendix Figure 3 This is a flowchart illustrating the specific process of butt welding two pipes in the existing technology.

[0023] Appendix Figure 4 This is a flowchart illustrating the specific process of butt welding two pipes according to the present invention.

[0024] Appendix Figure 5 This is a schematic diagram of butt welding of two pipes after overlay welding according to the present invention.

[0025] Appendix Figure 6 A schematic diagram of the welding of the butt joint of two weld overlay pipes.

[0026] Specific implementation examples:

[0027] 1. Pipe collection: Collect 16Mo3 pipes with specifications of Φ60.3*6.3, and polish and sandblast them.

[0028] 2. Pipe overlay welding: Use nickel-based welding wire ERNiCrMo-3 to overlay 2mm on the pipe surface.

[0029] 3. Beveling: First, the butt joints of the weld overlay pipes are flattened on a beveling machine so that the butt joints are perpendicular to the central axis of the weld overlay pipes. Then, the butt joints of the weld overlay pipes are beveled so that the beveling angle of each butt joint is 35° and the welding beveling angle of the two butt joints is 70°.

[0030] Welding Process: First, butt the two weld overlay pipes together, ensuring a zero gap. Use self-fusion welding to perform the first round of welding at the joint. The first layer of welding has a weld angle of 375°. During the welding process, the welding torch should not be oscillated. When the welding torch reaches the arc termination point for the first round of welding, remove the welding torch from the arc termination point. Once the weld temperature has cooled to no higher than 50°C, begin the second layer of welding. Use SFA5.28 ER70S-A1 Ø1.2mm welding wire for filler welding. The second layer of welding has a weld angle of 375°. During the welding process, the welding torch should not be oscillated. When the welding torch reaches the arc termination point for the second round of welding, remove the welding torch from the arc termination point. Once the weld temperature has cooled to no higher than 50°C, replace the welding torch with nickel-based weld overlay wire SFA5.14 ERNiCrMo-3 Ø1.2mm welding wire and begin the third and fourth layers of welding. Welding process: a. During the process, oscillate the welding torch along the bevel width, pausing for 0.2 seconds at the edge of the bevel; b. Turn on the hot wire function and adjust the hot wire current to 5A; c. The welding process for the third and fourth layers should be continuous without interruption. During the welding process, use the following formula to calculate the temperature distribution of the weld and its surrounding area:

[0031] ;

[0032] in, This indicates the temperature distribution in and around the weld. Represents the coordinates of the points corresponding to the temperature distribution. of Axis coordinates Represents the coordinates of the points corresponding to the temperature distribution. of Axis coordinates Represents the coordinates of the points corresponding to the temperature distribution. of Axis coordinates Indicates time, Indicates welding heat input, Represents pi (π). This indicates the thermal diffusivity of the weld overlay pipe. Indicates the coordinates of the welding torch position of Axis coordinates Indicates the coordinates of the welding torch position of Axis coordinates Indicates the coordinates of the welding torch position of Axis coordinates Represents a time variable that changes over time. Representing time variables The derivative of the temperature distribution is used to calculate the welding stress of the weld overlay pipe using the following formula:

[0033] ;

[0034] wherein, represents welding stress of the weld and the vicinity thereof, represents temperature distribution of the weld and the vicinity thereof, represents axis coordinates of the temperature distribution corresponding point coordinates , axis coordinates, represents axis coordinates of the temperature distribution corresponding point coordinates , axis coordinates, represents axis coordinates of the temperature distribution corresponding point coordinates , axis coordinates, represents elastic modulus of the cladding pipe, represents thermal expansion coefficient, represents Poisson's ratio. According to the welding stress, welding control in the welding process is optimized to ensure welding quality.

[0035] RT nondestructive testing is performed on the butt weld of the cladding pipe to obtain quality characteristics, characteristic parameters of the quality characteristics are calculated, and according to the characteristic parameters, the following formula is used to calculate the weld quality of the cladding pipe:

[0036] ;

[0037] wherein, represents weld quality, represents the i-th quality characteristic, represents the total number of quality characteristics, represents the i-th quality characteristic, represents the weight of the i-th quality characteristic, represents the characteristic parameter of the i-th quality characteristic, represents error. The pipe is automatically transported to the automatic pipe bender by the motion mechanism, and the pipe is bent according to the drawing and the program.

[0038] Subsequent processing work is performed.

[0039] Further, when the first round of welding is performed on the butt joint by self-fluxing welding, since the welding torch is stationary, the speed of the cladding pipe 1 rotating around the pipe in parallel is set as V1, and the speed of the cladding pipe 2 rotating around the pipe in parallel is set as V2, and V2>V1 is set.

[0040] Further, the inner diameter of the cladding pipe is set as Φ1, and the outer diameter of the cladding pipe is set as Φ2, then T1=πΦ1 / V1, T2=πΦ1 / V2, and T1 and T2 satisfy (T1-T2) / T2>0.2.

[0041] Further, the inner diameter of the cladding pipe is set as Φ1, and the outer diameter of the cladding pipe is set as Φ2, then T1=πΦ1 / V1, T2=πΦ1 / V2, and T1 and T2 satisfy (T1-T2) / T2>0.2. ​

[0042] Further, when starting the third layer and the fourth layer welding, the width of the bevel is L, the width of the bevel is divided into three parts, the middle third of the bevel is L1, the right edge of the right edge of the bevel to the middle bevel L1 is L2, and the left edge of the left edge of the bevel to the left edge of the middle bevel L1 is L3.

[0043] Further, the welding gun swings along the width of the bevel, the speed of swinging within L1 is V1, the speed of swinging within L2 is V2, and the speed of swinging within L3 is V3, and V1>V2=V3.

[0044] Further, L1 / V1=t1, L2 / V2=t2, (t2-t1) / t1>δ+0.2.

[0045] The parameters in step 4 are shown in the following table:

[0046]

[0047] Table 1

[0048] The above process of welding the butt joint of the two cladding pipes and the prior art are compared, the process of the present application is to groove the port of the two butt joint pipes, which is different from the direct alignment welding method of the two pipes in the prior art, so that the welding bevel angle of the two butt joint ports of the cladding pipes is 70°, which facilitates the welding of multiple layers in the bevel. By welding multiple layers in the bevel, i.e. the first layer of welding layer and the backing layer of the cladding pipe adopt the same pipe base material self-melting welding, i.e. a self-dissolving backing layer weld is formed in the groove of the two pipe butt joints, the second layer of welding adopts SFA5.28 ER70S-A1 Ø1.2mm welding wire and is cooled to 50°C after welding to 375°, i.e. a filler layer weld is formed at the bevel, and then a nickel-based cladding welding wire SFA5.14 ERNiCrMo-3 Ø1.2mm welding layer is welded. This method prevents the nickel-based cladding layer from entering the weld joint of the two pipes, and the groove welding method of the two pipes and the cladding layer covering the entire width of the pipe before the butt welding together make the backing layer weld and the filler layer weld cover the entire serpentine pipe. After welding according to the cladding process, the chemical composition performance of the nickel-based alloy weld can meet the requirements of corrosion-resistant cladding, effectively solving the problems in the prior art.

Claims

1. A welding process for welding a surfacing pipe by argon arc welding butt joint, comprising the following steps: (1) preparing the pipe according to the drawing; (2) surfacing the pipe; the surfacing layer covers the entire width of the pipe; (3) processing the surfacing pipe according to the drawing to form a groove; the end of the pipe is processed to be flat, and a groove with an angle of 35° and a root face of 0-0.5 mm is formed; and the welding groove angle after the butt joint of the two surfacing pipe butt joints is 70°; (4) welding using an automatic argon arc welding system; during welding, the welding torch is located at the top of the pipe within a range of ±5°; first, the two surfacing pipe butt joints are butt jointed to make the butt joint gap zero, and self-fluxing welding is used to weld the first layer of the butt joint; the welding degree of the first layer is 375°; during welding, the welding torch does not swing; when the welding torch of the first layer reaches the arc collection point, the welding torch is moved away from the arc collection point; when the temperature of the weld seam cools to not higher than 50℃, the second layer of welding is started; during welding, SFA5.28ER70S-A1 Ø1.2mm welding wire is used for filling; the welding degree of the second layer is 375°; during welding, the welding torch does not swing; when the welding torch of the second layer reaches the arc collection point, the welding torch is moved away from the arc collection point; when the temperature of the weld seam cools to not higher than 50℃, the nickel-based surfacing welding wire SFA5.14 ERNiCrMo-3 Ø1.2mm welding wire is replaced, and the third layer and the fourth layer of welding are started; the welding process is as follows: a. the welding torch swings along the groove width, and stops for 0.2s when reaching the edge of the groove; b. the hot wire function is turned on, and the hot wire current is adjusted to 5A; c. the third and fourth layers of welding are continuously welded without interruption; (4.1) assembling the pipes by the automatic argon arc welding system; (4.2) welding the base layer of the weld seam without adding wire, and using the self-fluxing of the base material; the base layer of the weld seam is 0.5-1mm lower than the surface of the base material; (4.3) using the welding wire matched with the base material of the pipe to weld the filler layer of the weld seam; (4.4) using the surfacing nickel-based alloy metal welding wire to weld the surfacing filler cap layer, which is welded on the filler layer of the weld seam. In step (4.2), the welding torch does not swing during the welding process; the base layer of the weld seam should be 5-15mm longer than the inner diameter of the pipe to ensure that the arc collection and starting points are staggered.

2. The surfacing pipe argon arc weld butt joint welding process of claim 1, wherein: In step (4.3), the welding torch does not swing during the welding process; the number of layers is set according to the thickness of the base material.

3. The surfacing pipe argon arc weld butt joint welding process of claim 1, wherein: In step (4.3), the filler layer of the weld seam is 5-15mm longer than the inner diameter of the pipe.

4. The surfacing pipe argon arc weld butt joint welding process of claim 1, wherein: In step (4.4), the welding torch swings during welding, and the welding wire needs to be heated to above 300℃ by resistance heating.

5. The surfacing pipe argon arc weld butt joint welding process of claim 1, wherein: In step (4.4), according to different requirements for the thickness of the surfacing layer, the surfacing filler layer is welded for more than one layer, and the surfacing filler layer and the surfacing cap layer are continuously welded without stopping the arc between each layer.

6. The surfacing tube TIG butt welding process of claim 1, wherein: In step (4.4), the cap layer of the weld seam is 10-15mm longer than the filler layer of the weld seam.

7. The surfacing pipe argon arc weld butt joint welding process of claim 1, wherein: In step (3), the groove angle of each surfacing pipe butt joint is 35°, and the welding groove angle after the butt joint of the two surfacing pipe butt joints is 70°.

8. The surfacing pipe argon arc weld butt joint welding process of claim 1, wherein: The surfacing pipe butt joint is subjected to RT non-destructive testing to ensure the quality of the weld seam.

9. The surfacing pipe argon arc weld butt joint welding process of claim 1, wherein: In step (3), the groove angle of each surfacing pipe butt joint is 35°, and the welding groove angle after the butt joint of the two surfacing pipe butt joints is 70°. The surfacing pipe butt joint is subjected to RT non-destructive testing to ensure the quality of the weld seam.

10. The surfacing pipe argon arc weld butt joint welding process of claim 1, wherein: The pipe is automatically conveyed to the automatic pipe bender by the moving mechanism, and is bent according to the drawing and procedure.

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