A root cleaning-free welding process for pressure vessels

Abstract

The present invention belongs to the field of welding, and discloses a method for welding without root cleaning of pressure vessels, comprising the following steps: S1, groove processing; S2, pretreatment; S3, assembly spot welding: the control assembly gap d after spot welding is still 0~1.5mm, and the upper and lower misalignment is controlled at 0~1.5 mm, and the spot welding excess height does not exceed 1mm; S4, base welding; S5, filling and cover welding: submerged arc welding is used to continue welding the Y-type welding groove after base welding on the front side, filling the Y-type welding groove and covering the surface to complete the welding; S6, post-weld heat treatment: after welding is completed, the workpiece to be welded is heat treated in the furnace to eliminate the residual stress after welding. The root cleaning-free welding method in the present invention processes the welding groove into a Y shape, and combines the shape of the Y-shaped welding groove, adopts single-sided K-TIG welding base to realize single-sided welding and double-sided forming, realizes root cleaning-free and double-sided welding-free in the welding process, has a small heat-affected zone, and has excellent welding quality.

Description

Technical Field

[0001] The invention belongs to the field of welding, and in particular relates to a root cleaning-free welding process for a pressure vessel. Background Art

[0002] In the field of pressure vessels, the welding of longitudinal and circumferential seams of medium and thick plate cylinders is an important part of product manufacturing. The traditional welding method of medium and thick plate cylinders generally adopts beveling, submerged arc welding on the front of the bevel, carbon arc gouging on the back of the bevel, grinding and welding again, or manual argon arc welding or arc welding for base, and then submerged arc welding for filling and covering. These welding processes all lead to low production efficiency, low welding quality, and large welding heat impact. Therefore, how to weld medium and thick plates in the field of pressure vessels quickly, with high quality and low heat impact is a technical problem that needs to be solved urgently. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a root cleaning-free welding process for pressure vessels, which does not require root cleaning, has high production efficiency and excellent welding quality.

[0004] The technical solution of the present invention is: a root cleaning-free welding method for a pressure vessel, comprising the following steps:

[0005] S1. Groove processing: Process the workpieces to be welded so that the two butted workpieces to be welded form a Y-shaped welding groove, wherein the thickness of the workpieces to be welded is ≥10 mm, the assembly gap d of the Y-shaped welding groove formed by the two workpieces to be welded is 0-1.5 mm, the blunt edge size h is 4.5-6 mm, the groove angle θ is 80°-90°, the side with the Y-shaped welding groove is the front side, the side with the blunt edge is the back side, and a groove is provided on the fixture below the back side of the workpieces to be welded;

[0006] S2. Pretreatment: Remove rust, cutting slag, burrs, oil stains, dirt and other debris from the workpiece to be welded;

[0007] S3, assembly spot welding: spot weld the two workpieces to be welded, and the assembly gap d after spot welding is still controlled to be 0-1.5 mm, and the upper and lower misalignment is controlled to be 0-1.5 mm, and the spot welding excess height does not exceed 1 mm;

[0008] S4, base welding: K-TIG welding is used to perform single-layer single-pass welding on the Y-shaped welding groove formed by the two workpieces to be welded, and single-sided welding is achieved. Shielding gas is introduced into the front and back of the workpieces to be welded. K-TIG welding adopts direct current positive connection, welding current is 480~500A, arc voltage is 16~18V, and welding speed is 18~22cm / min;

[0009] S5, filling and capping welding: Use submerged arc welding to continue welding on the front side of the Y-shaped welding groove after the base welding, fill the Y-shaped welding groove and complete the welding by capping. The filling welding is multi-layer single-pass welding, and the capping welding is single-layer multi-pass welding. Submerged arc welding adopts DC reverse connection, the welding current is 550~660A, the arc voltage is 23~30V, and the welding speed is 45~55cm / min;

[0010] S6. Post-weld heat treatment: After welding is completed, the workpiece to be welded is heat treated in a furnace to eliminate post-weld residual stress.

[0011] Furthermore, in step S4, two workpieces to be welded are placed on the operating table of the K-TIG welding machine, and the welding gun and the workpieces to be welded are adjusted to a vertical position for front welding.

[0012] Furthermore, in step S4, the front protective gas is 99.99% Ar with a flow rate of 20-25 L / min, and the back protective gas is 99.99% Ar with a flow rate of 8-10 L / min.

[0013] Further, in step S4, in the K-TIG single-layer single-pass welding, segmented current and voltage welding is adopted: in the length direction of the workpiece to be welded, the welding current of the two end parts is 490A≤I1≤500A, the arc voltage is 17V≤V1≤18V, the welding speed is 20≤υ1≤22cm / min, the front shielding gas is 99.99%Ar, the flow rate is 20~25L / min, and the back shielding gas is 99.99%Ar, and the flow rate is 8~10L / min; the welding current of the middle part is 480A≤I2<490A, the arc voltage is 16V≤V2<17V, the welding speed is 18≤υ2<20cm / min, the front shielding gas is 99.99%Ar, the flow rate is 20~25L / min, and the back shielding gas is 99.99%Ar, and the flow rate is 8~10L / min.

[0014] Furthermore, in step S5, the filling welding is 2-3 layers, the welding current of each layer is 550-600A, the arc voltage is 23-27V, and the welding speed is 45-50 cm / min.

[0015] Furthermore, in step S5, the cap welding is a single-layer double-pass welding, and the welding current, welding voltage and welding speed of the first weld are all greater than those of the second weld.

[0016] Furthermore, in step S5, the welding current of the first weld of the cap welding is 600A≤I3≤620A, the welding voltage is 26V≤V3≤28V, and the welding speed is 50 cm / min≤υ3≤52 cm / min; the welding current of the second weld is 580A≤I4<600A, the welding voltage is 24V≤V3<26V, and the welding speed is 48 cm / min ≤υ3<50 cm / min.

[0017] Furthermore, in step S6, when the workpiece to be welded is put into the furnace at a temperature below 400°C, the heating rate of the heat treatment furnace is 56-220°C / h, the holding temperature is 530-560°C, the holding time is 30-35 minutes, the cooling rate is 56-280°C / h, and then the furnace is cooled and the workpiece is taken out of the furnace at a temperature below 400°C to complete the post-weld heat treatment.

[0018] The beneficial technical effects of the present invention are:

[0019] The root cleaning-free welding method of the present invention processes the welding groove into a Y shape, and combined with the shape of the Y-shaped welding groove, a single-sided K-TIG welding base is used to achieve single-sided welding and double-sided forming, thereby achieving root cleaning-free and double-sided welding-free welding, saving workpiece clamping procedures, and significantly improving welding efficiency. K-TIG welding does not require a filler wire, saves welding materials, and cooperates with subsequent filling and capping welding on the same side, and adjusts welding process parameters according to different welding positions and sequences, and adopts segmented current and voltage welding, so that the strength and impact performance of the welded joint meet relevant requirements, and the welding quality is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the process flow chart of the root cleaning-free welding of pressure vessels;

[0021] Figure 2 It is a schematic diagram of the Y-shaped groove of the workpiece to be welded;

[0022] In the figure,

[0023] 1. Workpiece to be welded. DETAILED DESCRIPTION

[0024] In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples. The following examples are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0025] See also Figure 1-2 This specific embodiment provides a pressure vessel root cleaning-free welding method, which is suitable for welding thick plate cylinders, especially for welding pressure vessel cylinders. The welding method includes the following steps:

[0026] S1. Groove processing: Process the workpieces to be welded so that the two butted workpieces to be welded form a Y-shaped welding groove, wherein the thickness of the workpieces to be welded is ≥10 mm, and the preferred thickness of the workpieces to be welded is 10 mm to 18.2 mm. The side with the Y-shaped welding groove is the front side, and the side with the blunt edge is the back side. A groove is provided on the fixture below the back side of the workpiece to be welded for heat dissipation.

[0027] In this specific example, the material of the workpiece to be welded is stainless steel or low alloy steel; the specific stainless steel materials are S30408, S30403, S31608, S31603, 304 and 316L, etc., and the low alloy steels are Q245R, Q345R, 16MnDR, SA-516Gr.60, SA-516Gr.70, SA-612, P460NL1, etc. Figure 2 The assembly gap d of the Y-shaped welding groove formed by the two workpieces to be welded is 0~1.5mm, the blunt edge size h is 4.5~6mm, and the groove angle θ is 80°~90°. The welding process of this specific embodiment is particularly suitable for welding workpieces to be welded with a Y-shaped groove close to a right angle.

[0028] S2. Pretreatment: Remove rust, cutting slag, burrs, oil stains, dirt and other debris from the workpiece to be welded. Pretreatment before welding can reduce the occurrence of welding defects and help improve the quality of the welded joint.

[0029] S3. Assembly spot welding: Spot weld the two workpieces to be welded together, and the assembly gap d after spot welding is still controlled to be 0~1.5mm, and the upper and lower misalignment is controlled to be 0~1.5mm, and the spot welding excess height does not exceed 1mm.

[0030] S4. Base welding: Use K-TIG welding to perform single-layer single-pass welding on the Y-shaped welding groove formed by the two workpieces to be welded, and make one-sided welding through. Shielding gas is introduced into the front and back of the workpieces to be welded.

[0031] The specific operating parameters are as follows: Place the two workpieces to be welded on the K-TIG welding machine operating table, adjust the welding gun and the workpieces to be welded to a vertical position, and weld from the front. K-TIG welding uses direct current positive connection, the welding current is 480~500A, the arc voltage is 16~18V, the welding speed is 18~22cm / min, the front shielding gas is 99.99%Ar, the flow rate is 20~25L / min, and the back shielding gas is 99.99%Ar, the flow rate is 8~10L / min. After welding is completed, check the front and back weld formation, and perform filling and cap welding if qualified.

[0032] In particular, in this specific embodiment, the front and back sides of the workpiece to be welded are filled with protective gas, and the front protective gas flow rate is controlled to be 20-25 L / min, and the back protective gas flow rate is 8-10 L / min. The coordination of protective gas with different flow rates on the front and back sides ensures an all-round inert gas atmosphere without causing turbulence, thereby ensuring welding quality. In this embodiment, K-TIG welding is a single-layer single-pass welding, which is used to weld the blunt edge portion of the Y-shaped groove.

[0033] Among them, K-TIG welding adopts segmented current and voltage welding in single-layer single-pass welding: in the length direction of the workpiece to be welded, the welding current at both ends is 490A≤I1≤500A, the arc voltage is 17V≤V1≤18V, the welding speed is 20≤υ1≤22cm / min, the front shielding gas is 99.99%Ar, the flow rate is 20~25L / min, and the back shielding gas is 99. 99%Ar, flow rate is 8~10L / min, the heat dissipation of the two end parts is strong, and the larger welding current and voltage ensure the stable performance of the welding keyhole; the welding current of the middle part is 480A≤I2<490A, the arc voltage is 16V≤V2<17V, the welding speed is 18≤υ2<20cm / min, the front shielding gas is 99.99%Ar, the flow rate is 20~25L / min, and the back shielding gas is 99.99%Ar, the flow rate is 8~10L / min. Due to the heat accumulation in the middle part and the poor heat dissipation performance in the middle position, a smaller welding current and voltage are used. This specific embodiment takes into account the welding efficiency, penetration and welding keyhole stability through the segmented welding process adopted in K-TIG deep penetration welding.

[0034] S5. Filling and capping welding: Use submerged arc welding to continue welding on the front side of the Y-type welding groove after the base welding, fill the Y-type welding groove and cap it to complete the welding. The filling welding is a multi-layer single-pass welding, and the capping welding is a single-layer multi-pass welding.

[0035] In filling and capping welding: submerged arc welding uses DC reverse connection, welding current is 550~660A, arc voltage is 23~30V, welding speed is 45~55cm / min. In filling and capping welding, after each welding, the welding slag needs to be cleaned before the next welding, until the Y-shaped welding groove is filled and capped; the filling welding is 2-3 layers, and the capping welding is a single-layer double-pass welding;

[0036] In filling welding, the welding current is 550~600A, the arc voltage is 23~27V, and the welding speed is 45~50 cm / min;

[0037] In the cover welding, in order to minimize the influence of heat accumulation on the weld, the welding current, welding voltage and welding speed of the first weld are greater than those of the second weld. The welding current of the first weld is 600A≤I3≤620A, the welding voltage is 26V≤V3≤28V, and the welding speed is 50 cm / min≤υ3≤52 cm / min. The welding current of the second weld is 580A≤I4<600A, the welding voltage is 24V≤V3<26V, and the welding speed is 48 cm / min ≤υ3<50 cm / min.

[0038] S6. Post-weld heat treatment: After welding is completed, the workpiece to be welded is put into the furnace when the temperature is lower than 400℃. The heating rate of the heat treatment furnace is 56-220℃ / h, the holding temperature is 530-560℃, the holding time is 30-35 minutes, the cooling rate is 56-280℃ / h, and then the furnace is cooled. When the temperature is lower than 400℃, the workpiece is taken out of the furnace to complete the post-weld heat treatment.

[0039] The root cleaning-free welding process for pressure vessels of the present invention is described below through specific embodiments. Example

[0040] In Example 1, two workpieces 1 to be welded are used. Both of the workpieces 1 to be welded have a length of 0.5 m, a thickness of 18.2 mm, and are made of P460NL1 and are in a plate shape.

[0041] S1. Groove processing: Process the workpieces 1 so that the groove of each workpiece 1 is a 1 / 2 Y-shaped groove, and the two workpieces 1 are butted to form a Y-shaped welding groove.

[0042] In this step, the groove is machined and formed, and the assembly gap d of the Y-shaped welding groove is 0.5 mm, the blunt edge size h is 4 mm, and the groove angle θ is 85°.

[0043] S2. Pretreatment: Remove rust, cutting slag, burrs, oil stains, dirt and other debris from the workpiece 1 to be welded.

[0044] S3, assembly spot welding: The two workpieces 1 are assembled and spot welded to position the two workpieces 1. Specifically, the control gap d of the two workpieces 1 after assembly is still 0.5 mm, and there is no misalignment, and the weld seam excess height of the spot welding is 0.6 mm.

[0045] S4, base welding: K-TIG welding is used to weld the Y-shaped welding groove. Specifically, the two workpieces 1 to be welded after being assembled and positioned are placed on the workbench of the K-TIG welding machine, and the position of the workpiece 1 to be welded is adjusted so that the K-TIG welding gun is vertically located directly above the part to be welded. During base welding, K-TIG welding adopts direct current positive connection. In the length direction of the workpiece to be welded, the welding current at both ends is 495A, the arc voltage is 17.5V, and the welding speed is 21cm / min. The welding current in the middle part is 485A, the arc voltage is 16.5V, and the welding speed is 19 cm / min. The front shielding gas is 99.99% Ar, and the flow rate is 25L / min. The back shielding gas is 99.99% Ar, and the flow rate is 15L / min.

[0046] S5. Filling and capping welding: Check the front and back sides of the weld of the base welding. If qualified, perform filling and capping welding. Use submerged arc welding to continue welding the Y-shaped welding groove after the base welding from the front, fill the Y-shaped welding groove and cap it to complete the welding.

[0047] In the steps of filling and capping welding: submerged arc welding DC reverse connection is adopted, the welding current is 550~640A, the arc voltage is 23~29V, the welding speed is 45~50cm / min, and the consumption of submerged arc welding wire is 1.03kg / m, and the flux is 1.2kg / m.

[0048] Among them, the filling welding is a 2-3 layer single pass welding, and the cap welding is a single layer double pass welding; in the filling welding, the welding current is 550~600A, the arc voltage is 23~27V, and the welding speed is 45~50 cm / min;

[0049] In the cap welding, the welding current of the first weld is 630A, the welding voltage is 28V, and the welding speed is 49cm / min. The welding current of the second weld is 600A, the welding voltage is 27V, and the welding speed is 48 cm / min. In the cap welding, considering the heat accumulation of the first weld, reducing the welding parameters of the second weld can significantly reduce welding deformation and improve welding quality.

[0050] In the welding method of this embodiment, after K-TIG base welding is performed from the front side, there is no need to clean the back side again, and submerged arc welding is directly performed. The total welding time of K-TIG welding and submerged arc welding is 6 minutes.

[0051] S6. Post-weld heat treatment: After welding is completed, the workpiece to be welded is put into the furnace when the temperature is lower than 400℃. The heating rate of the heat treatment furnace is 56-220℃ / h, the insulation temperature is 530-560℃, the insulation time is 30-35 minutes, the cooling rate is 56-280℃ / h, and then the furnace is cooled. When the temperature is lower than 400℃, the workpiece is taken out of the furnace to complete the post-weld heat treatment.

[0052] The present invention aims at workpieces to be welded made of materials with higher thermal conductivity. By improving the heat dissipation conditions and the covering process, the K-TIG combined submerged arc welding process parameter window can be effectively widened, making the welding "keyhole" more stable. A targeted heat treatment process is formulated to help stabilize the weld formation, reduce residual stress, and broaden the scope of use of the K-TIG welding method.

[0053] The welded joint after welding in Example 1 was subjected to a tensile test, a bending test and an impact test. The test results are shown in Table 1:

[0054] Table 1 Mechanical properties of welded joint after welding in Example 1

[0055]

[0056] It can be concluded from Table 1 that the mechanical properties of the welded joints of Example 1 after welding all meet the requirements of ASME Code Section IX, and the welding quality is excellent.

[0057] In Comparative Example 1, the two workpieces 1 to be welded are both 0.5 m long, 18.2 mm thick, made of P460NL1 and in plate shape.

[0058] S1. Groove processing: The workpieces 1 to be welded are processed so that the groove of each workpiece 1 is a 1 / 2 Y-shaped groove, and the two workpieces 1 are butted to form a Y-shaped welding groove. The gap d of the Y-shaped welding groove is 0.5 mm, the blunt edge size h is 4 mm, and the groove angle θ is 85°.

[0059] S2. Pretreatment: Remove rust, cutting slag, burrs, oil stains, dirt and other debris from the workpiece 1 to be welded.

[0060] S3, spot welding: The two workpieces 1 are spot welded to position the two workpieces 1. The gap between the two workpieces 1 to be welded is 0.5 mm, and there is no misalignment. The weld seam height of the spot welding is 0.6 mm.

[0061] S4. Submerged arc welding: After the front welding is completed, the back is cleaned and then submerged arc welding is used. The total time consumed for the above welding is 10 minutes for the front submerged arc welding and 15 minutes for the back cleaning. The materials used for submerged arc welding are as follows: 1.8 kg / m of submerged arc welding wire and 2.1 kg / m of flux are consumed.

[0062] By comparing the above-mentioned Example 1 with the comparative example 1, it can be concluded that the root cleaning-free welding method in the present application greatly improves the welding efficiency, and because K-TIG welding does not require filler wire, it saves 0.77kg / m of submerged arc welding wire and 0.9kg / m of flux (excluding energy consumption and auxiliary material consumption); at the same time, it reduces the working hours of root cleaning and grinding, avoids dust and noise pollution caused by root cleaning and grinding, improves the working environment of workers, and reduces the working intensity of workers.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for welding a pressure vessel without cleaning the root, characterized in that: The following steps are involved: S1. Groove processing: Process the workpieces to be welded so that the two butted workpieces to be welded form a Y-shaped welding groove, wherein the thickness of the workpieces to be welded is ≥10 mm, the assembly gap d of the Y-shaped welding groove formed by the two workpieces to be welded is 0-1.5 mm, the blunt edge size h is 4.5-6 mm, the groove angle θ is 80°-90°, the side with the Y-shaped welding groove is the front side, the side with the blunt edge is the back side, and a groove is provided on the fixture below the back side of the workpieces to be welded; S2. Pretreatment: Remove rust, cutting slag, burrs, oil stains, dirt and other debris from the workpiece to be welded; S3, assembly spot welding: spot weld the two workpieces to be welded, and the assembly gap d after spot welding is still controlled to be 0-1.5 mm, and the upper and lower misalignment is controlled to be 0-1.5 mm, and the spot welding excess height does not exceed 1 mm; S4, base welding: K-TIG welding is used to perform single-layer single-pass welding on the Y-shaped welding groove formed by the two workpieces to be welded, and single-sided welding is achieved. Shielding gas is introduced into the front and back of the workpieces to be welded. K-TIG welding adopts direct current positive connection, welding current is 480~500A, arc voltage is 16~18V, and welding speed is 18~22cm / min; S5, filling and capping welding: Use submerged arc welding to continue welding on the front side of the Y-shaped welding groove after the base welding, fill the Y-shaped welding groove and complete the welding by capping. The filling welding is multi-layer single-pass welding, and the capping welding is single-layer multi-pass welding. Submerged arc welding adopts DC reverse connection, the welding current is 550~660A, the arc voltage is 23~30V, and the welding speed is 45~55cm / min; S6. Post-weld heat treatment: After welding, the workpiece to be welded is heat treated in a furnace to eliminate residual stress after welding; Wherein, in step S4, in K-TIG single-layer single-pass welding, segmented current and voltage welding is adopted: in the length direction of the workpiece to be welded, the welding current of the two end parts is 490A≤I1≤500A, the arc voltage is 17V≤V1≤18V, the welding speed is 20≤υ1≤22cm / min, the front shielding gas is 99.99%Ar, the flow rate is 20~25L / min, and the back shielding gas is 99.99%Ar, and the flow rate is 8~10L / min; the welding current of the middle part is 480A≤I2<490A, the arc voltage is 16V≤V2<17V, the welding speed is 18≤υ2<20cm / min, the front shielding gas is 99.99%Ar, the flow rate is 20~25L / min, and the back shielding gas is 99.99%Ar, and the flow rate is 8~10L / min; In step S5, the cap welding is a single-layer double-pass welding, and the welding current, welding voltage and welding speed of the first weld are all greater than those of the second weld; the welding current of the first weld of the cap welding is 600A≤I3≤620A, the welding voltage is 26V≤V3≤28V, and the welding speed is 50 cm / min≤υ3≤52 cm / min, and the welding current of the second weld is 580A≤I4<600A, the welding voltage is 24V≤V3<26V, and the welding speed is 48 cm / min ≤υ3<50 cm / min.

2. A method for welding a pressure vessel without cleaning according to claim 1, characterized in that: In step S4, two workpieces to be welded are placed on the operating table of the K-TIG welding machine, the welding gun and the workpieces to be welded are adjusted to a vertical position, and welding is performed from the front.

3. A method for welding a pressure vessel without cleaning according to claim 1, characterized in that: In step S5, the filling welding is 2-3 layers, the welding current of each layer is 550-600A, the arc voltage is 23-27V, and the welding speed is 45-50 cm / min.

4. A method for welding a pressure vessel without cleaning according to claim 1, characterized in that: In step S6, when the workpiece to be welded is put into the furnace at a temperature below 400°C, the heating rate of the heat treatment furnace is 56-220°C / h, the holding temperature is 530-560°C, the holding time is 30-35 minutes, the cooling rate is 56-280°C / h, and then the furnace is cooled and the workpiece is taken out of the furnace at a temperature below 400°C to complete the post-weld heat treatment.

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