Low-carbon steel pipeline K-TIG defect-free arc suppression process

Abstract

The low-carbon steel pipeline K-TIG defect-free arc suppression process comprises the following steps that (1) a low-carbon steel pipeline to be welded with the wall thickness being 6-13 mm is subjected to groove machining, an I-shaped groove or a groove with steps is adopted in one side, and an elbow self-carried groove is adopted in the other side; (2) assembling the low-carbon steel to-be-welded pipe fittings in pairs; (3) before welding, introducing Ar into the back parts of the low-carbon steel to-be-welded pipe fittings, and adopting 99.99% pure argon to the front surfaces and the back surfaces of the low-carbon steel to-be-welded pipe fittings; (4) a K-TIG welding gun is used for aligning the edge of the straight groove of the assembled low-carbon steel pipeline to be welded under the protection of Ar gas on the front face and the back face, and the distance between the end of a tungsten needle in the welding gun and the surface of a workpiece is adjusted to be 0.5-1 mm; and (5) a K-TIG welding gun is used for conducting deep fusion backing welding under the protection of Ar gas, and welding parameters are controlled in stages.

Description

Technical Field

[0001] The invention relates to a K-TIG defect-free arc closing process for a low-carbon steel pipeline. Background Art

[0002] In the production process of pipelines and pressure vessels, medium and thick plates (6-13mm) of low carbon steel are widely used for welding. According to actual production conditions, submerged arc welding, argon arc welding and manual arc welding are the three most commonly used welding methods. However, these three types of welding have great limitations. Submerged arc welding cannot achieve single-sided welding and double-sided forming, and the back side must be air-planed or the back side must be primed with manual argon arc welding; ordinary argon arc welding has a shallow melting depth and low cladding efficiency, and grooves must be opened for multi-layer and multi-pass welding; manual arc welding has a slow welding speed and is difficult to control welding quality. Slag knocking is required after each welding pass, which greatly reduces production efficiency.

[0003] Deep penetration argon arc welding (K-TIG) is a high-speed full penetration welding technology that does not require wire filling, groove opening, or professional technical operators. It can perform single-pass deep penetration welding on materials with a thickness of 16 mm at a speed 100 times faster than traditional fusion welding technology. Therefore, K-TIG has begun to replace traditional fusion welding and has opened up comprehensive applications in the pipeline and pressure vessel industries. At present, in the K-TIG welding process of pipelines and pressure vessels, due to the plasma jet force caused by high current, it is easy to produce pores or collapse defects at the arc closing process of the pipeline, which affects the welding quality of the entire pipeline and container and hinders the application of K-TIG in the field of low-carbon steel pipelines and pressure vessels. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention proposes a K-TIG defect-free arc closure process for a low-carbon steel pipeline to solve the problem of arc closure defects in the current K-TIG welding.

[0005] The present invention solves the above technical problems by providing a K-TIG defect-free arc closure process for a low-carbon steel pipeline, comprising the following steps: (1) Bevel the low-carbon steel pipe to be welded with a wall thickness of 6-13 mm, with an I-type bevel or a stepped bevel on one side and a bevel with an elbow on the other side; (2) Assemble the low carbon steel pipe fittings to be welded; (3) Before welding, Ar is introduced into the back of the low-carbon steel pipe to be welded, and 99.99% pure argon is used on the front and back sides; (4) Use a K-TIG welding gun with Ar gas protection on both sides, aim at the straight bevel edge of the assembled low-carbon steel pipe to be welded, and adjust the end of the tungsten needle in the welding gun above the workpiece surface; (5) Use a K-TIG welding gun to perform deep penetration welding under Ar gas protection, and control the welding parameters in stages.

[0006] The technical solution further defined in the present invention is: Preferably, the chemical composition of the (1) low carbon steel is as follows by weight percentage: C: 0.03%-0.25%, Mn: ≤2.0%, Si: ≤1.0%, S: ≤0.01%, P: ≤0.045%, and the remainder is Fe and unavoidable impurities.

[0007] Preferably, in step (2), the low carbon steel pipe fittings to be welded are assembled in pairs. After the assembly, a argon arc welding gun is used under the protection of Ar gas to perform parent metal autogenous welding at the bottom of the blunt edge of the welding end of the workpiece to be welded by manual argon arc welding to form a spot weld to fix the pipeline. Spot welding is performed every 80-120 mm, the assembly gap is ≤0.5 mm, and the assembly error is ≤1.5 mm.

[0008] Preferably, in step (4), the straight bevel edge of the assembled low-carbon steel pipe to be welded is aligned, and the end of the tungsten needle in the welding gun is adjusted to 0.5-1 mm above the workpiece surface.

[0009] Preferably, in step (5), a K-TIG welding gun is used to perform deep penetration root welding under Ar gas protection, the welding current is 400-525A, the welding speed is 24-35cm / min, and the shielding gas flow rate is 20-35L / min.

[0010] Preferably, the staged control in step (5) specifically includes: In the first stage, the welding current is 400-525A, the welding speed is 24-35cm / min, and the heat input is enough to penetrate the wall thickness without causing the molten pool to collapse; In the second stage, the heat input is increased by 20% and maintained at a distance of 8mm 10mm before arc closure; In the third stage, after the arc overlap, the heat input is further increased by 15% and the distance is maintained at 8mm; The fourth stage reduces heat input by 30% and maintains a distance of 2mm; After completing the second to fourth stage parameter operation, it takes 2-5 seconds to reduce the current from the last stage setting value to the arc extinction current of 60A. Beneficial Effects

[0011] The present invention is aimed at the deep fusion welding of low-carbon steel pipelines. According to its unique groove form, the K-TIG welding process is adjusted to reasonably optimize the welding parameter combination of the arc closing position. During the keyhole closing process, the arc plasma is discharged from the back of the weld through the enlarged keyhole, combined with the precise enlargement and reduction control of the heat input, so that the keyhole closing becomes smoother and the generation of welding arc closing defects is avoided. The method is highly operational and easy to form an automatic control standardized approach, which has a strong guiding significance for actual on-site production. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the carbon steel pipeline groove assembly diagram of Example 1; Figure 2 This is the carbon steel pipe groove assembly diagram of Example 2 Figure 3 This is a welding effect diagram without using the process of the present invention; Figure 4 This is a diagram showing the welding effect using the process of the present invention. DETAILED DESCRIPTION Example

[0013] This embodiment provides a low-carbon steel pipeline K-TIG defect-free arc closure process, including the following steps: (1) The A106B low-carbon steel pipe to be welded with a wall thickness of 6.5 mm is grooved. One side adopts an I-type groove, that is, no groove is opened, and only milling is performed by a machine tool. The other side adopts an elbow with a 35-degree groove and a 1.5 mm blunt edge; the gap between the two welding ends is 0.1-0.3 mm, and the misalignment size is 0.2-1 mm; (2) Assemble the low-carbon steel pipe fittings to be welded, and use manual argon arc welding to perform self-melting welding of the base material at the bottom of the blunt edge of the welding end of the workpiece to be welded to form a spot weld to fix the pipeline. Spot welding is performed every 120 mm. (3) Before welding, Ar is introduced into the back of the low-carbon steel pipe to be welded, and 99.99% pure argon is used on the front and back sides; (4) Use a K-TIG welding gun with Ar gas protection on both sides, align it with the center of the weld of the assembled A106B carbon steel pipe to be welded, and adjust the end of the tungsten needle in the welding gun to 0.5 mm above the workpiece surface; (5) Use a K-TIG welding gun to perform deep penetration welding under Ar gas protection, and control the welding parameters in stages. The control parameters of welding are shown in Table 1: Table 1: 6.5mm carbon steel pipe welding parameters In the first stage, the welding heat input is controlled to penetrate the wall thickness without causing the molten pool to collapse; At the point where the arc closing and arc starting points are about to overlap, enter the second stage and start increasing the heat input 10mm in advance, increase the heat input by 20% and maintain the distance of 8mm (about 1.9 seconds); After the arc ending and arc starting overlap, continue to increase the heat input by about 15% and maintain the distance of 8mm (about 2.2 seconds); After completing the third stage parameter operation, the normal current decay process begins, and it takes 5 seconds to reduce the current from the last stage setting value to the arc extinction current of 60A. Example

[0014] This embodiment provides a low-carbon steel pipeline K-TIG defect-free arc closure process, including the following steps: (1) The A106B low-carbon steel pipe to be welded with a wall thickness of 12 mm is grooved. One side uses a large blunt groove, that is, a 45-degree groove with an 8 mm blunt edge, and the other side uses an elbow with a 35-degree groove and a 1.5 mm blunt edge; the gap between the two welding ends is 0.1-0.3 mm, and the misalignment size is 0.2-1 mm; (2) Assemble the A106 low carbon steel pipe fittings to be welded, and use manual argon arc welding to perform autogenous welding of the base material at the bottom of the blunt edge of the welding end of the workpiece to be welded to form a spot weld to fix the pipeline. Spot welding is performed every 120 mm. (3) Before welding, Ar is introduced into the back of the low-carbon steel pipe to be welded, and 99.99% pure argon is used on the front and back sides; (4) Use a K-TIG welding gun with Ar gas protection on both sides, align it with the center of the weld of the assembled A106B carbon steel pipe to be welded, and adjust the end of the tungsten needle in the welding gun to 0.5 mm above the workpiece surface; Use a K-TIG welding gun to perform deep penetration root welding under Ar gas protection, and control the welding parameters in stages. The control parameters of welding are shown in Table 2: Table 2: 12mm carbon steel pipe welding parameters In the first stage, the welding heat input is controlled to penetrate the wall thickness without causing the molten pool to collapse; At the point where the arc closing and arc starting points are about to overlap, start increasing the heat input 10 mm in advance, increase the heat input by 20% and maintain a distance of 8 mm (approximately 1.9 seconds); After the arc ending and arc starting overlap, continue to increase the heat input by about 15% and maintain the distance of 8mm (about 2.4 seconds); After completing the third stage, reduce the heat input by about 30% compared with the third stage and maintain a distance of 2 mm (about 1.2 seconds); After completing the fourth stage parameter operation, the normal current decay process begins, and it takes 2 seconds to reduce the current from the last stage setting value to the arc extinction current of 60A.

[0015] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A K-TIG defect-free arc closure process for a low-carbon steel pipeline, characterized by: The following steps are involved: (1) Bevel the low-carbon steel pipe to be welded with a wall thickness of 6-13 mm, with an I-type bevel or a stepped bevel on one side and a bevel with an elbow on the other side; (2) Assemble the low carbon steel pipe fittings to be welded. (3) Before welding, Ar is introduced into the back of the low-carbon steel pipe to be welded, and 99.99% pure argon is used on the front and back sides; (4) Use a K-TIG welding gun with Ar gas protection on both sides, aim at the straight bevel edge of the assembled low-carbon steel pipe to be welded, and adjust the end of the tungsten needle in the welding gun above the workpiece surface; (5) Use a K-TIG welding gun to perform deep penetration welding under Ar gas protection, and control the welding parameters in stages.

2. A K-TIG defect-free arc closure process for low-carbon steel pipeline according to claim 1, characterized in that: The chemical composition of the (1) medium-low carbon steel is as follows by weight percentage: C: 0.03%-0.25%, Mn: ≤2.0%, Si: ≤1.0%, S: ≤0.01%, P: ≤0.045%, and the balance is Fe and unavoidable impurities.

3. A K-TIG defect-free arc closure process for low-carbon steel pipeline according to claim 1, characterized in that: In the step (2), the low carbon steel pipe fittings to be welded are assembled in pairs. After the assembly, a argon arc welding gun is used under the protection of Ar gas to perform parent material self-melting welding at the bottom of the blunt edge of the welding end of the workpiece to be welded by manual argon arc welding to form a spot weld to fix the pipeline. Spot welding is performed every 80-120 mm, the assembly gap is ≤0.5 mm, and the assembly error is ≤1.5 mm.

4. A K-TIG defect-free arc closure process for low-carbon steel pipeline according to claim 1, characterized in that: In the step (4), the center of the weld of the assembled low-carbon steel pipe to be welded is aligned, and the end of the tungsten needle in the welding gun is adjusted to 0.5-1 mm above the surface of the workpiece.

5. The K-TIG defect-free arc closure process for low-carbon steel pipeline according to claim 1 is characterized by: In the step (5), a K-TIG welding gun is used to perform deep penetration root welding under Ar gas protection, the welding current is 400-525A, the welding speed is 24-35cm / min, and the shielding gas flow rate is 20-35L / min.

6. A K-TIG defect-free arc closure process for low-carbon steel pipeline according to claim 1, characterized in that: The step (5) of staged control specifically includes: In the first stage, the welding current is 400-525A, the welding speed is 24-35cm / min, and the heat input is enough to penetrate the wall thickness without causing the molten pool to collapse; In the second stage, the heat input is increased by 20% and maintained at a distance of 8mm 10mm before arc closure; In the third stage, after the arc overlap, the heat input is further increased by 15% and the distance is maintained at 8mm; The fourth stage reduces heat input by 30% and maintains a distance of 2mm; After completing the second to fourth stage parameter operation, it takes 2-5 seconds to reduce the current from the last stage setting value to the arc extinction current of 60A.

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