A method of welding carbon steel pipe

Abstract

The present application relates to the technical field of welding, in particular to a carbon steel pipe welding method, the carbon steel pipe welding method of the present application first welds a positioning weld at the butt joint of two carbon steel pipes to be processed in a layered welding manner, by setting the length of each layer of the positioning weld to gradually decrease from inside to outside, the two ends of the positioning weld can form a stepped slope, then the stepped slope at the two ends of the positioning weld is polished into a straight line slope, and then backing welding and outer layer welding are performed; the polishing amount when polishing the stepped slope into a straight line slope is small, the polishing time of the positioning weld is shortened, and the welding efficiency of the carbon steel pipe is improved.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a method for welding carbon steel pipes. Background Technology

[0002] During shipbuilding and repair, prefabrication welding of carbon steel pipe butt joints is required. Welding carbon steel pipes involves first symmetrically welding multiple tack welds, followed by the root pass and outer pass welds. After the tack welds, the ends of the tack welds need to be ground into a bevel to ensure the connection strength between the root pass and the tack welds. Currently, tack welds are often performed using single-layer welding with a relatively thick layer. Therefore, the grinding amount required for the beveled ends of the tack welds is substantial. Furthermore, the confined space at the butt joint makes this process difficult, resulting in a lengthy grinding operation and low welding efficiency for carbon steel pipes. Summary of the Invention

[0003] The technical problem to be solved by the present invention is that: at present, the method of single-layer welding with a relatively thick welding thickness is used for tack welding. The amount of grinding is large when grinding the slope at the end of the tack weld, resulting in low welding efficiency of carbon steel pipe.

[0004] To solve the above-mentioned technical problems, the purpose of this invention is to provide a method for welding carbon steel pipes, characterized by comprising the following steps:

[0005] Step S1: Weld a tack weld at the joint of the two carbon steel pipes to be processed by layer welding. The length of each layer of the tack weld decreases from the inside to the outside, so that the two ends of the tack weld form a stepped slope.

[0006] Step S2: Grind the stepped slopes at both ends of the positioning weld into straight slopes;

[0007] Step S3: Perform a root weld at the joint to form a root weld.

[0008] Step S4: Weld an outer layer weld on the outside of the locating weld.

[0009] As a preferred embodiment, in step S1: each of the sub-welds is welded using a metal powder-cored flux-cored wire in the manner of metal active gas shielded welding.

[0010] As a preferred embodiment, in step S1: when tack welding each of the sub-welds, the two carbon steel pipes are rotated synchronously to adjust the area being tack welded to face upwards, so that the molten carbon steel pipe base material at the tack weld is subjected to gravity and flows towards the inside of the carbon steel pipe, so that the tack weld solidifies into an arc-shaped structure that is concave towards the inside of the carbon steel pipe.

[0011] As a preferred embodiment, in step S3: during the root pass welding, the two carbon steel pipes are rotated synchronously to adjust the area where the root pass welding is being performed to face upwards, so that the molten carbon steel pipe base material at the root pass weld is caused by gravity to flow towards the inside of the carbon steel pipe, so that the root pass weld solidifies into an arc-shaped structure that is concave towards the inside of the carbon steel pipe.

[0012] As a preferred embodiment, in step S3: during the root pass welding, the two carbon steel pipes are continuously rotated to form a closed ring structure in the root pass weld.

[0013] As a preferred embodiment, in step S3:

[0014] The rotation angle range of the two carbon steel pipes is greater than or equal to 362° and less than or equal to 368°.

[0015] As a preferred embodiment, the outer weld seam includes a filler weld seam and a capping weld seam arranged sequentially from the inside to the outside, and in step S4:

[0016] During filler and capping welding, the welding torch is held above both carbon steel pipes, and the two carbon steel pipes are rotated synchronously.

[0017] As a preferred embodiment, in step S4:

[0018] The central angle corresponding to the arc between the arc starting position of the filler weld and the arc starting position of the root weld is greater than or equal to 90° and less than or equal to 180°.

[0019] As a preferred embodiment, in step S4:

[0020] The central angle corresponding to the arc between the arc initiation position of the cover weld and the arc initiation position of the fill weld is greater than or equal to 90° and less than or equal to 180°.

[0021] As a preferred embodiment, in step S4, when performing filler welding and capping welding, the rotation angle range of both carbon steel pipes is greater than or equal to 365° and less than or equal to 371°.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The carbon steel pipe welding method of the present invention uses a layered welding method to weld a tack weld at the butt joint of two carbon steel pipes to be processed. The length of each layer of the tack weld decreases from the inside to the outside, which can form a stepped slope at both ends of the tack weld. Then, the stepped slope at both ends of the tack weld is ground into a straight slope, followed by the root pass welding and the outer layer welding. The grinding amount when grinding the stepped slope into a straight slope is smaller, which shortens the slope grinding time of the tack weld and improves the welding efficiency of the carbon steel pipe. Attached Figure Description

[0024] Figure 1 This is a flowchart of the carbon steel pipe welding method of the present invention;

[0025] Figure 2 This is a schematic cross-sectional view of the positioning weld in the thickness direction before grinding.

[0026] Figure 3 This is a schematic diagram of the cross-section along the length of the positioning weld before the slope is ground in the positioning weld of this invention.

[0027] Figure 4 This is a schematic diagram of the cross-section along the length of the positioning weld after the bevel has been ground.

[0028] Figure 5 This is a cross-sectional view of the overall weld of the present invention after the cover weld;

[0029] In the diagram, 1 is a carbon steel pipe, 2 is a tack weld, 21 is a sub-weld, 3 is a stepped slope, 4 is a straight slope, 5 is a root pass weld, 6 is an outer layer weld, 61 is a filler weld, and 62 is a cap weld. Detailed Implementation

[0030] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "top," "bottom," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be understood that the terms "first," "second," etc., are used in this invention to describe various information, but this information should not be limited to these terms; these terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this invention, "first" information can also be referred to as "second" information, and similarly, "second" information can also be referred to as "first" information.

[0032] like Figures 1 to 5 As shown, a preferred embodiment of the carbon steel pipe welding method of the present invention includes the following steps:

[0033] Step S1: Weld a tack weld 2 at the joint of the two carbon steel pipes to be processed by layer welding. The length of each layer of sub-weld 21 of the tack weld 2 decreases from the inside to the outside, so that the two ends of the tack weld 2 form a stepped slope 3.

[0034] Step S2: Grind the stepped slopes 3 at both ends of the positioning weld 2 into straight slopes 4; Step S3: Perform root welding at the butt joint to form root weld 5;

[0035] Step S4: Weld the outer layer weld 6 on the outside of the locating weld 2.

[0036] When the stepped slope 3 is ground into a straight slope 4, the amount of grinding is smaller, which shortens the slope grinding time for tack welding and improves the welding efficiency of carbon steel pipe 1.

[0037] In this embodiment, in step S1: each sub-weld 21 is welded using a metal powder-cored flux-cored wire in the manner of metal active gas shielded welding.

[0038] Specifically, metal active gas shielded welding, also known as MAG welding, is performed using metal powder-cored flux-cored welding wire. This type of wire contains a large amount of metal powder, resulting in high deposition efficiency during welding. Furthermore, the chemical composition and mechanical properties of the metal powder-cored flux-cored wire can be flexibly adjusted as needed, making it well-suited for high-strength and specially required carbon steel pipes. In addition, the metal spatter produced during welding is minimal and does not easily adhere to the weld surface, thus not affecting the quality of subsequent welds. It eliminates the need to completely remove the spatter from the weld surface before continuing to weld. Moreover, MAG welding offers high welding efficiency, a short welding cycle, low argon gas consumption, and low overall construction costs.

[0039] In this embodiment, to facilitate the subsequent root pass welding, in step S1, during the tack welding of each sub-weld 21, both carbon steel pipes 1 are rotated simultaneously to adjust the area being tack welded to an upward orientation. This causes the molten carbon steel pipe 1 base material at the tack weld 2 to flow inward under gravity, resulting in the tack weld 2 solidifying into an arc-shaped structure concave inward of the carbon steel pipe 1. The groove formed by the arc-shaped structure concave inward of the carbon steel pipe 1 can accommodate the welding liquid for the subsequent root pass welding, which is beneficial to improving the welding quality of the root pass welding.

[0040] To facilitate welding, in this embodiment, the root pass welding is performed using a continuous welding method. Specifically, in step S3: during the root pass welding, the two carbon steel pipes 1 are continuously rotated so that the root pass weld 5 forms a closed ring structure.

[0041] In this embodiment, in step S3:

[0042] The rotation angle range of the two carbon steel pipes 1 is greater than or equal to 362° and less than or equal to 368°.

[0043] Specifically, when performing the root pass welding on carbon steel pipe 1, the welding is performed continuously in a clockwise direction. The rotation degree of carbon steel pipe 1 during welding is set to 365±3°, so that the welding end point and the welding start point of the root pass welding coincide. This can solve the technical problem that the welding end point and the welding start point cannot be fully penetrated due to the low starting temperature when only rotating 360°.

[0044] In this embodiment, the outer weld 6 includes a filler weld 61 and a cap weld 62 arranged sequentially from the inside to the outside. In step S4:

[0045] During filler and cover welding, the welding torch is held above the two carbon steel pipes 1, and the two carbon steel pipes 1 are rotated synchronously. The welding torch is always positioned downwards to avoid the decline in welding quality caused by the downward flow of welding liquid due to gravity during vertical or horizontal welding.

[0046] To ensure the welding quality of the filler weld 61, in this embodiment, in step S4:

[0047] The central angle between the arc starting position of the filler weld and the arc starting position of the root weld is greater than or equal to 90° and less than or equal to 180°.

[0048] To ensure the welding quality of the cover weld 62, in this embodiment, in step S4:

[0049] The central angle between the arc starting position of the cover weld and the arc starting position of the fill weld is greater than or equal to 90° and less than or equal to 180°.

[0050] Specifically, in this embodiment, the arc initiation positions of the filler weld and the root weld are staggered, and the arc initiation positions of the cover weld and the filler weld are also staggered. This prevents localized stress concentration at the weld joint, improves welding quality, and reduces post-weld residual stress concentration and residual deformation. This ensures the welding quality of the cover weld 62 and the filler weld 61. In this embodiment, a V-groove is used for the welding bevel, and the root weld, filler weld, and cover weld are all performed using a multi-pass welding method. Both the filler and cover welds are performed using active gas shielded welding with metal-cored flux-cored wire. No slag removal is required during the root weld, each filler weld, and each cover weld, greatly improving welding efficiency.

[0051] In this embodiment, during step S4, when performing filler and capping welds, the rotation angle range of both carbon steel pipes 1 is greater than or equal to 365° and less than or equal to 371°.

[0052] Specifically, when performing filler welding on carbon steel pipe 1, welding is carried out continuously in a clockwise direction. The rotation degree of carbon steel pipe 1 during welding is set to 368±3°, so that the welding end point and welding start point of the filler weld coincide. This solves the technical problem that the junction area between the welding end point and welding start point cannot be fully penetrated due to the low starting temperature when rotating only 360°. When performing capping welding on carbon steel pipe 1, welding is carried out continuously in a clockwise direction. The rotation degree of carbon steel pipe 1 during welding is set to 368±3°, so that the welding end point and welding start point of the capping weld coincide. This solves the technical problem that the junction area between the capping weld end point and capping weld start point cannot be fully penetrated due to the low starting temperature when rotating only 360°.

[0053] In this embodiment, during the root pass, fill pass, and cover pass welding, each weld layer does not require segmented symmetrical welding construction. The welding of the entire circumference of the same layer can be carried out continuously, resulting in high welding efficiency, fewer weld joints, and a simple welding process.

[0054] The welding parameters for welding carbon steel pipes with wall thicknesses from 6mm to 20mm are as follows:

[0055]

[0056]

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for welding carbon steel pipes, characterized in that, Includes the following steps: Step S1: Weld a positioning weld (2) at the butt joint of two carbon steel pipes (1) to be processed by layer welding. The length of each layer of sub-welds (21) of the positioning weld (2) decreases from the inside to the outside, so that the two ends of the positioning weld (2) form a stepped slope (3). Step S2: Grind the stepped slopes (3) at both ends of the positioning weld (2) into straight slopes (4); Step S3: Perform root welding at the joint to form a root weld (5); Step S4: Weld an outer layer weld (6) on the outside of the locating weld (2); In step S3: during the root pass welding, the two carbon steel pipes (1) are rotated synchronously to adjust the area being welded to face upwards, so that the molten carbon steel pipe (1) base material at the root pass weld (5) flows into the carbon steel pipe (1) under the action of gravity, so that the root pass weld (5) solidifies into an arc-shaped structure that is concave into the carbon steel pipe (1); during the root pass welding, the two carbon steel pipes (1) are rotated continuously to form a closed ring structure of the root pass weld (5); the rotation angle range of the two carbon steel pipes (1) is greater than or equal to 362° and less than or equal to 368°.

2. The carbon steel pipe welding method according to claim 1, characterized in that, In step S1: each of the sub-welds (21) is welded using metal powder-cored flux-cored wire in the manner of metal active gas shielded welding.

3. The carbon steel pipe welding method according to claim 1, characterized in that, In step S1: When tack welding each of the sub-welds (21), the two carbon steel pipes (1) are rotated synchronously to adjust the area being tack welded to face upwards, so that the molten carbon steel pipe (1) base material at the tack weld (2) flows into the carbon steel pipe (1) under the action of gravity, so that the tack weld (2) solidifies into an arc-shaped structure that is concave into the carbon steel pipe (1).

4. The carbon steel pipe welding method according to claim 1, characterized in that, The outer weld (6) includes a filler weld (61) and a cap weld (62) arranged sequentially from the inside to the outside. In step S4: When performing filler and cover welding, the welding torch is held above the two carbon steel pipes (1) and the two carbon steel pipes (1) are rotated synchronously.

5. The carbon steel pipe welding method according to claim 4, characterized in that, In step S4: The central angle corresponding to the arc between the arc starting position of the filler weld and the arc starting position of the root weld is greater than or equal to 90° and less than or equal to 180°.

6. The carbon steel pipe welding method according to claim 4, characterized in that, In step S4: The central angle corresponding to the arc between the arc initiation position of the cover weld and the arc initiation position of the fill weld is greater than or equal to 90° and less than or equal to 180°.

7. The carbon steel pipe welding method according to claim 4, characterized in that, In step S4, when performing filler welding and cover welding, the rotation angle range of the two carbon steel pipes (1) is greater than or equal to 365° and less than or equal to 371°.

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