Single-side welding and double-side forming welding construction method for large-diameter water supply pipeline

Abstract

The invention provides a single-face welding and double-face forming welding construction method for a large-diameter water supply pipeline. The single-face welding and double-face forming welding construction method comprises the following steps that S10, beveling is conducted, specifically, a carbon steel pipeline connector is beveled; s20, the pipeline enters the pit; s30, assembling, wherein longitudinal welding seams of the assembled carbon steel pipelines should be staggered; s40, spot welding is carried out, wherein symmetric spot welding is carried out on the root of the groove of the assembled carbon steel pipeline; the manual electric arc welding and one-side welding double-side forming technology is adopted, follow welding, filling welding and cosmetic welding are sequentially carried out on the groove of the carbon steel pipeline after spot welding in the pipe, and welding of the connector of the carbon steel pipeline is completed; and S60, welding quality inspection is conducted. By the adoption of the welding construction method, welding is conducted from the front face of the groove in the carbon steel pipeline, uniform and neat welding seams which are regular in shape and accord with quality can be obtained on the front face and the back face of the groove, and the carbon steel pipeline welding problem that due to shallow excavation of a foundation pit and limited operation space, double-face welding cannot be achieved, but full penetration welding is required is solved.

Description

Technical Field

[0001] The invention belongs to the field of pipeline construction, and in particular relates to a single-sided welding and double-sided forming welding construction method for a large-diameter water supply pipeline. Background Art

[0002] When the water supply pipeline is constructed directly above the urban subway, in order to ensure the safety of subway operation, the relevant management department at the higher level requires that "in principle, it is not recommended to carry out deep excavation and construction of retaining piles or other engineering piles directly above the subway structure". Such external conditions as the above limit the depth of foundation pit excavation or make it impossible to carry out foundation pit excavation, especially for large-diameter pipes, such as carbon steel pipes with a pipe diameter D of not less than 800mm and a pipe wall thickness of 16 to 36mm. Due to the space limitation of the construction site, double-sided welding of such large-diameter pipes cannot be achieved. Summary of the invention

[0003] In view of this, the present invention aims to propose a single-sided welding and double-sided forming welding construction method for large-diameter water supply pipelines, so as to achieve the welding of large-diameter carbon steel pipelines when the construction site is limited and the full-section excavation and double-sided welding of the pipeline cannot be performed.

[0004] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0005] The single-sided welding and double-sided forming welding construction method for large-diameter water supply pipelines includes the following steps:

[0006] S10: Beveling:

[0007] Beveling of carbon steel pipe joints is performed to make the groove formed after the pipe joints are connected into a V-shaped groove, with the larger opening of the V-shaped groove facing the center of the pipe;

[0008] S20: Pipeline entering the pit:

[0009] Lift the carbon steel pipe into the foundation pit, and remove impurities within a range of not less than 10 to 20 mm from the groove surface and the inner and outer surfaces of the groove. There must be no cracks or interlayer defects;

[0010] S30: Pairs:

[0011] Adjust the carbon steel pipes. After adjustment, the longitudinal welds of the carbon steel pipes should be staggered. The center deviation of the carbon steel pipes after adjustment should not exceed 20% of the pipe wall thickness and should not be greater than 2mm.

[0012] S40: Spot welding:

[0013] Symmetrical spot welding is performed on the groove roots of the carbon steel pipes to fix the carbon steel pipes. The spot welding positions are no less than four and avoid the longitudinal welds and spiral welds of the carbon steel pipes. The spot welding seam thickness is consistent with the base layer welding thickness set for the butt welding of the carbon steel pipes.

[0014] S50: Welding:

[0015] Manual arc welding and single-sided welding and double-sided forming processes are used to perform follow welding, filling welding and cover welding on the grooves of the carbon steel pipes assembled inside the pipe to complete the welding of the carbon steel pipe interfaces;

[0016] S60: Welding quality inspection:

[0017] Perform non-destructive testing on the welds of the interface welding to determine whether the welding is qualified. If it is unqualified, the welding must be repaired and then determined whether the welding is qualified.

[0018] Furthermore, in step S10, the root gap c of the V-shaped groove is 3-4 mm, the blunt edge p is 1.5 mm, and the groove angle α is 60±1°.

[0019] Furthermore, in step S30, the longitudinal welds of the assembled carbon steel pipes are located at 45° to the left and right of the vertical symmetry axis of the upper semicircle of the pipes.

[0020] Furthermore, in step S40, the spot welding length is 80-100 mm, and the spot welding spacing is not greater than 400 mm.

[0021] Furthermore, the welding rods used in this welding method must be dried before welding. The alkaline welding rods are dried at a temperature of 350-400°C for 1 hour. After heating, the welding rods are stored in a 100-150°C insulation barrel for standby use. The welding rods cannot be dried repeatedly more than twice.

[0022] Furthermore, step S35 is provided between step S30 and step S40, and step S45 is provided between step S40 and step S50. The contents of step S35 and step S45 are both preheating. When the pipeline temperature is lower than 0°C, in step S35 and step S45, the area within 100mm on both sides of the groove must be heated and dried by fire welding, and the carbon steel pipeline must be preheated to above 15°C before welding.

[0023] Furthermore, in step S50, the base layer starts to strike an arc from the left end of the groove. After the arc is ignited, the welding rod pauses for a few seconds to preheat, and then swings horizontally to the right to weld. When the arc reaches the right front edge of the groove, the welding rod is pressed down and paused for a few seconds until a molten hole is formed.

[0024] Furthermore, after the arc is struck, under the action of the high temperature and blowing force of the arc, the left end of the root of the groove melts and breaks down to form a molten hole. The welding rod must be immediately lifted to about 1.5 mm away from the molten pool, and then normal welding can be carried out to the right.

[0025] Furthermore, in step S50, the arc is always in front of the molten iron during the welding process.

[0026] Furthermore, in step S50, during the welding process, when the electrode is about to be used up and needs to be replaced, the electrode is pulled back about 10 to 15 mm in the opposite direction of welding, and the electrode is quickly lifted up so that the arc gradually lengthens and quickly extinguishes.

[0027] Compared with the prior art, the large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method described in the present invention has the following advantages:

[0028] By adopting the welding construction method of the present invention, the pipeline groove is assembled toward the center of the pipeline, and single-sided welding and double-sided forming welding operations are implemented in the carbon steel pipeline, that is, follow welding, filling welding and cover welding are performed on the pipeline groove in the pipeline, and regular, uniform and neat welds that meet the quality can be obtained on both the front and back sides of the groove, thereby solving the problem of carbon steel pipeline welding that cannot be double-sided welded due to shallow foundation pit excavation and limited working space, but requires full penetration. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0030] Figure 1 A roadmap of a single-sided welding and double-sided forming welding construction method for a large-diameter water supply pipeline according to an embodiment of the present invention;

[0031] Figure 2 Schematic diagram of the V-groove structure in an embodiment of the present invention.

[0032] Description of reference numerals: DETAILED DESCRIPTION

[0033] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0034] The single-sided welding and double-sided forming welding construction method for large-diameter water supply pipelines is applied to the butt welding of carbon steel pipelines with a pipe diameter D not less than 800mm and a pipe wall thickness δ of 16 to 36mm. In order to ensure the strength of the pipeline after welding, the straight pipe section of the pipeline should not be spliced ​​with short sections less than 800mm in length. The welding process of this welding construction method is as follows Figure 1 As shown, the following steps are included:

[0035] S10: Beveling:

[0036] The carbon steel pipe interface is beveled so that the bevel formed by the pipe joints, that is, the assembled pipes, is a V-shaped bevel, and the large mouth of the V-shaped bevel faces the center of the pipe.

[0037] V-shaped groove structure Figure 2 As shown, the root gap c of the V-shaped groove is 3-4 mm, the blunt edge p is 1.5 mm, and the groove angle α is 60±1°.

[0038] S20: Pipeline entering the pit:

[0039] Use a truck crane to hoist the carbon steel pipe into the foundation pit, and remove impurities within a range of not less than 10 to 20 mm on the groove surface and the inner and outer surfaces of the groove of the carbon steel pipe. There must be no cracks or interlayer defects;

[0040] S30: Pairs:

[0041] Use hydraulic jack to adjust the carbon steel pipe. After adjustment, the longitudinal welds of the carbon steel pipes should be staggered, and the staggered spacing should not be less than 300mm. For example, the longitudinal welds of the carbon steel pipes should be adjusted to 45° to the left and right of the vertical symmetry axis of the upper semicircle of the pipe, so that there should be no cross welds at any position of the pipe. After adjustment, the center deviation of the carbon steel pipes should not exceed 20% of the pipe wall thickness and should not be greater than 2mm.

[0042] S40: Spot welding:

[0043] Check the interface of the carbon steel pipe to make sure it is clean and tidy, then spot weld the groove root of the carbon steel pipe symmetrically, and then fix the carbon steel pipe. The spot welding position should be no less than four, the spot welding spacing should not be greater than 400mm, and the spot welding length should be 80-100mm. The spot welding position should avoid the longitudinal weld and spiral weld of the carbon steel pipe. The spot welding weld thickness should be consistent with the base layer welding thickness set for the carbon steel pipe joint welding. In this step, the spot welding electrode should be the same as the subsequent interface welding electrode.

[0044] S50: Welding:

[0045] Manual arc welding and single-sided welding and double-sided forming technology are used to perform follow welding, filling welding and cover welding on the groove of the carbon steel pipeline in the pipeline to complete the welding of the carbon steel pipeline interface.

[0046] In this welding step, after each layer of welding, the electric hand grinding wheel is used to clean the root to ensure the welding quality. After welding, the weld surface excess height is no more than 3mm, and the excess part is polished.

[0047] During welding operations, pay attention to the following 5 aspects to improve welding quality:

[0048] First: Control the arc striking position:

[0049] The arc is struck at the left end of the groove for the base layer. After the arc is ignited, the electrode should be paused for a while to preheat, and then swung horizontally to the right for welding. When the arc reaches the right front edge of the groove, the electrode is pressed down and paused for a few seconds until a molten hole is formed.

[0050] Second: Control the size of the melt hole:

[0051] Under the high temperature and blowing force of the arc, the root of the groove melts and breaks through to form a molten hole. The welding rod should be immediately lifted to about 1.5mm away from the molten pool, and then normal welding can be carried out to the right.

[0052] Third: Control the flow direction of molten iron and slag:

[0053] During welding, the arc should always be in front of the molten iron. The directional blowing force of the gas generated by the arc and the melting of the coating is used to blow the molten iron to the back of the molten pool. This can ensure the depth of fusion and the separation of slag from the molten iron, reducing the possibility of slag inclusion and pores. When welding, pay attention to the condition of the molten pool. The front of the molten pool is slightly concave, the molten iron is relatively calm, and darker lines emerge from the molten pool and gradually gather to the upper back of the molten pool. This is the slag. If the molten pool is ahead, that is, the arc is behind the molten pool, it is easy to get slag inclusion.

[0054] Fourth: Control the fusion on both sides of the groove:

[0055] During the welding process, the fusion of the groove surface must be observed at any time. It must be clearly seen that the groove surface melts and mixes with the deposited metal of the electrode to form a molten pool. The edge of the molten pool must be fused with the groove surfaces on both sides. It is best to have a small pit in front of the molten pool, but it can be filled with molten iron immediately. Otherwise, the fusion will be poor and cracks will easily occur during back bending.

[0056] Fifth: Control the quality of the weld joint and the bottom weld:

[0057] When the welding rod is about to be finished and needs to be replaced, pull the welding rod back about 10-15mm in the opposite direction of welding, and quickly lift the welding rod to gradually lengthen the arc and quickly extinguish it. This can eliminate the shrinkage hole at the end of the arc or bring it to the surface of the weld so that it can be melted when the next welding rod is welded. Note that the burn-back time should not be too long and try to make the joint into a bevel.

[0058] S60: Welding quality inspection:

[0059] Perform non-destructive testing on the welds of the interface welding to determine whether the welding is qualified. The testing is divided into appearance testing and non-destructive testing. If the test is qualified, it will enter the subsequent heat treatment process. If it is unqualified, the welding will be repaired and then judged whether the welding is qualified.

[0060] In the welding method of the present invention, in order to improve the welding effect of the welding rod, the welding rod used must be dried before welding. The alkaline welding rod is dried at a temperature of 350-400°C for 1 hour. After heating, the welding rod is stored in a constant temperature box at a temperature of 100-150°C for insulation. It can be used at any time. When using, pay attention to keep it dry. The welding rod cannot be dried repeatedly more than twice.

[0061] In the welding method of the present invention, when the temperature of the pipeline is lower than 0°C, in order to improve the quality of pipeline welding, the pipeline needs to be preheated to increase the temperature of the pipeline to a suitable welding temperature for positive temperature welding. Therefore, step S35 is provided between step S30 and step S40, and step S45 is provided between step S40 and step S50. The contents of step S35 and step S45 are both preheating. In step S35 and step S45, the area within 100mm on both sides of the groove must be heated and dried by fire welding, and the carbon steel pipeline must be preheated to above 15°C before welding. Continuous welding is required during welding. The heating of the preheating area should ensure that the heating area is heated evenly, prevent additional stress on the joint caused by local heating, ensure that the heating rate is uniform and controllable, and prevent overheating of the parent material.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. Single-sided welding and double-sided forming welding construction method for large-diameter water supply pipelines, characterized by: The following steps are involved: S10: Beveling: Beveling of carbon steel pipe joints is performed to make the groove formed after the pipe joints are connected into a V-shaped groove, with the larger opening of the V-shaped groove facing the center of the pipe; S20: Pipeline entering the pit: Lift the carbon steel pipe into the foundation pit, and remove impurities within a range of not less than 10 to 20 mm from the groove surface and the inner and outer surfaces of the groove. There must be no cracks or interlayer defects; S30: Pairs: Adjust the carbon steel pipes. After adjustment, the longitudinal welds of the carbon steel pipes should be staggered. The center deviation of the carbon steel pipes after adjustment should not exceed 20% of the pipe wall thickness and should not be greater than 2mm. S40: Spot welding: Symmetrical spot welding is performed on the groove roots of the carbon steel pipes to fix the carbon steel pipes. The spot welding positions are no less than four and avoid the longitudinal welds and spiral welds of the carbon steel pipes. The spot welding seam thickness is consistent with the base layer welding thickness set for the butt welding of the carbon steel pipes. S50: Welding: Manual arc welding and single-sided welding and double-sided forming processes are used to perform follow welding, filling welding and cover welding on the grooves of the carbon steel pipes assembled inside the pipe to complete the welding of the carbon steel pipe interfaces; S60: Welding quality inspection: Perform non-destructive testing on the welds of the interface welding to determine whether the welding is qualified. If it is unqualified, the welding must be repaired and then determined whether the welding is qualified.

2. According to claim 1, the large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method is characterized by: In step S10, the root gap c of the V-shaped groove is 3-4 mm, the blunt edge p is 1.5 mm, and the groove angle α is 60±1°.

3. The large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method according to claim 1 is characterized by: In step S30, the longitudinal welds of the carbon steel pipes are located at 45° to the left and right of the vertical symmetry axis of the upper semicircle of the pipe.

4. The large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method according to claim 1 is characterized in that: In step S40, the spot welding length is 80-100 mm, and the spot welding spacing is not greater than 400 mm.

5. The large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method according to claim 1 is characterized in that: The welding rods used in this welding method must be dried before welding. The alkaline welding rods should be dried at a temperature of 350-400℃ for 1 hour. After heating, the welding rods should be stored in a 100-150℃ insulation barrel for use. The welding rods should not be dried repeatedly more than twice.

6. The large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method according to claim 1 is characterized in that : Step S35 is provided between step S30 and step S40, and step S45 is provided between step S40 and step S50. The contents of step S35 and step S45 are both preheating. When the temperature of the pipeline is lower than 0°C, in step S35 and step S45, the area within 100mm on both sides of the groove must be heated and dried by fire welding, and the carbon steel pipeline must be preheated to above 15°C before welding.

7. The large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method according to claim 1 is characterized by: In step S50, the base layer starts to strike an arc from the left end of the groove. After the arc is ignited, the electrode pauses for a few seconds to preheat, and then swings horizontally to the right to weld. When the arc reaches the right front edge of the groove, the electrode is pressed down and paused for a few seconds until a molten hole is formed.

8. The large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method according to claim 7 is characterized in that: After the arc is struck, under the action of the high temperature and blowing force of the arc, the left end of the root of the groove melts and breaks down to form a molten hole. The welding rod must be immediately lifted to about 1.5mm away from the molten pool, and then normal welding can be carried out to the right.

9. The large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method according to claim 1 is characterized by: In step S50, the arc is always in front of the molten iron during the welding process.

10. The large-diameter water supply pipeline single-sided welding and double-sided forming welding construction method according to claim 1 is characterized in that: In step S50, during the welding process, when the electrode is about to be welded and needs to be replaced, the electrode is pulled back about 10 to 15 mm in the opposite direction of welding, and the electrode is quickly lifted up so that the arc gradually lengthens and quickly extinguishes.

Images