A pressure-resistant welding method for annular seam of pressure vessel

Abstract

The invention discloses a pressure-resistant welding method for annular seams of pressure vessels, which relates to the field of welding methods, including pre-treatment of both sides of the annular seams before welding, pre-deformation according to the conditions of the parent material, local preheating, selection of welding materials with specific components and adjustment of equipment parameters, multi-layer and multi-pass welding processes, insulation and slow cooling, radiographic detection, and overall heat treatment after welding to eliminate stress, and finally local induction heating of the weld and heat-affected zone and application of mechanical vibration to further reduce residual stress. It can reduce welding deformation, improve dimensional accuracy, enhance weld toughness, crack resistance, fatigue resistance and compressive strength, extend the service life of the container, and reduce residual stress.

Description

Technical Field

[0001] The invention relates to the field of welding methods, in particular to a pressure-resistant welding method for annular seams of pressure vessels. Background Art

[0002] In the modern industrial field, pressure vessels are a key equipment widely used in many industries such as petrochemical, electric power, and energy. The production processes of these industries often involve extreme working conditions such as high temperature, high pressure, and strong corrosion, which puts extremely high demands on the safety and reliability of pressure vessels. Circumferential welding is a key link in the manufacture of pressure vessels, and its welding quality is directly related to the overall performance and operational safety of pressure vessels.

[0003] Traditional pressure vessel girth welding technology has gradually exposed some limitations when faced with increasingly complex working conditions and strict quality standards.

[0004] In terms of welding deformation control, for pressure vessels of different materials and sizes, targeted pre-deformation treatment has not been carried out according to their specific characteristics. This leads to the fact that during the welding process, due to the effect of thermal stress, the annular seam is prone to large deformation, which not only affects the appearance quality of the pressure vessel, but is also likely to cause dimensional deviation, affecting the subsequent assembly and performance. In terms of welding joint performance, conventional welding materials and processes are difficult to meet the requirements for weld strength, toughness and corrosion resistance under high temperature and high pressure environments. Under such extreme working conditions, the mechanical properties of ordinary welding materials will be significantly reduced, and the welds are prone to defects such as cracks and corrosion, which shortens the service life of the pressure vessel and increases safety hazards. In terms of welding stress elimination, the existing technical means are not perfect. Although the traditional overall heat treatment method can reduce the residual stress of the weld to a certain extent, it is not effective in treating local stress concentration areas. These local high stress areas are prone to the initiation and expansion of fatigue cracks during equipment operation, which seriously threatens the safe operation of the pressure vessel.

[0005] With the continuous development of industry, the performance and quality requirements of pressure vessels are getting higher and higher. For example, in the petrochemical industry, new production processes require pressure vessels to withstand higher pressures and more complex chemical media corrosion; in the field of new energy, such as pressure vessels in nuclear fusion experimental devices, the requirements for welding quality and reliability have reached an almost harsh level.

[0006] Therefore, it is urgent to develop a new pressure vessel circumferential seam pressure-resistant welding method that can effectively control welding deformation, improve welding joint performance, comprehensively eliminate welding stress and ensure weld quality. This is of great significance for improving the safety, reliability and service life of pressure vessels and promoting the development of related industrial fields. Summary of the invention

[0007] The purpose of the present invention is to provide a pressure-resistant welding method for the annular seam of a pressure vessel, which includes pre-treating both sides of the annular seam, pre-deforming according to the condition of the parent material, and then locally preheating. Welding materials with specific compositions are selected and equipment parameters are adjusted. A multi-layer and multi-pass welding process is adopted. After welding, the stress is eliminated by heat preservation and slow cooling, X-ray detection, and overall heat treatment. Finally, the weld and the heat-affected zone are locally inductively heated and mechanical vibration is applied to further reduce the residual stress, thereby achieving pressure-resistant welding and improving the weld quality and the service life of the container.

[0008] To achieve the above object, the present invention provides the following technical solutions: A pressure-resistant welding method for annular seams of pressure vessels, characterized in that it comprises the following steps: S1: Preparation before welding; S2: pre-deformation control; S3: local preheating; S4: Select welding materials; S5: Adjust welding equipment parameters; S6: Post-welding treatment.

[0009] Step S1: Preparation before welding: Pre-treatment is to pre-treat the 20-30mm range on both sides of the annular seam of the pressure vessel to be welded, specifically to remove oil stains and rust impurities on the surface by mechanical grinding, use sandpaper with a particle size of 80-120 mesh, grind until the surface reveals a metallic luster, make the surface roughness reach Ra10-Ra15μm, and wipe with an organic solvent.

[0010] Step S2 pre-deformation control specifically includes pre-deformation treatment of the parent material on both sides of the annular seam according to the material, size and design requirements of the pressure vessel; For thinner plates with a thickness of 10-20mm, a mechanical pre-bending method is used, and the pre-bending curvature is controlled to produce a pre-bending amount of 0.5-1.5mm per meter length; For plates with a thickness of 20-50mm, the pre-stretching method is adopted, and the tensile stress is controlled between 10%-20% of the material yield strength. The stretching time is 5-10 minutes, so that the deformation of the annular seam after welding and the pre-deformation offset each other, reducing the final welding deformation and improving the dimensional accuracy and appearance quality of the pressure vessel.

[0011] Step S3 local preheating is specifically to preheat the local area of ​​the annular seam of the pressure vessel before welding begins. For pressure vessels made of Q345R material, when the wall thickness is 10-20mm, the preheating temperature is controlled at 100-150°C; when the wall thickness is 20-50mm, the preheating temperature is controlled at 150-200°C. The preheating is performed by surrounding the annular seam with an annular heating belt with a width of 50-80mm. The heating time is set to 15-30 minutes according to the size and thickness of the heating area to reduce the cooling rate of the weld joint, reduce the hardened structure in the weld metal, and improve the toughness and crack resistance of the weld.

[0012] Step S4 selects welding materials, specifically, according to the material, specification and design pressure requirements of the pressure vessel, selects appropriate welding materials; the impact toughness of the deposited metal at -10°C-10°C is not less than 34J, the carbon content in the chemical composition is 0.12%-0.18%, the manganese content is 1.20%-1.60%, the silicon content is 0.20%-0.50%, and the sulfur and phosphorus contents are not more than 0.035%.

[0013] Step S5 adjusts the welding equipment parameters. Specifically, for manual arc welding, the welding current is set to 140-180A, the welding voltage is set to 24-28V, and the welding speed is controlled at 18-22mm / min according to the welding material and the thickness of the weldment; for gas shielded welding, the wire feeding speed is set to 4-6m / min, and the CO2 gas flow rate is adjusted to 18-22L / min to ensure stable combustion of the welding arc and achieve good droplet transition.

[0014] Step S6 post-welding treatment specifically includes covering the weld with insulation cotton with a thickness of 30-50mm, slowly cooling the weld to room temperature, the cooling time is not less than 2 hours, and after cooling to room temperature, the weld is inspected by radiographic inspection, and the weld that passes the inspection is subjected to stress relief treatment. The pressure vessel is placed in a heat treatment furnace as a whole by an overall heat treatment method, and the heating rate is controlled at 30-50℃ / h, and heated to 580-620℃. The insulation time is calculated according to the wall thickness of the container, and the insulation time is 1 hour for every 25mm wall thickness, and the insulation time is not less than 2 hours. Then the pressure vessel is cooled with the furnace, and the cooling rate is controlled at 20-30℃ / h. The residual stress of the weld is reduced to below 100MPa, and the weld surface is polished to reduce the surface roughness of the weld to Ra3.2-Ra6.3μm.

[0015] The welding material is based on the composition of conventional low-alloy steel welding rods, with added nickel content of 0.8%-1.2%, chromium content of 0.5%-0.8%, and molybdenum content of 0.2%-0.4%, which improves the strength, toughness and corrosion resistance of the weld metal, can maintain good mechanical properties under high temperature and high pressure environments, and effectively extends the service life of the pressure vessel.

[0016] The welding adopts multi-layer and multi-pass welding process, and the base welding adopts tungsten inert gas arc welding. During base welding, the welding current is controlled at 80-100A, the arc voltage is 10-12V, and the welding speed is 8-12mm / min to ensure that the root of the weld is completely fused, and the thickness of the base weld is controlled at 3-4mm. During multi-layer and multi-pass welding, the welding directions of the two adjacent layers of welds are staggered with an angle of 45°-75°. The staggered welding method effectively disrupts the crystallization direction of the weld, refines the grains, reduces the formation of columnar crystals, and significantly improves the fatigue resistance and compressive strength of the weld, so that the weld is not prone to fatigue cracks when the pressure vessel is subjected to alternating loads.

[0017] After the overall heat treatment, the weld and heat-affected zone are locally induction heated. The heating temperature is controlled at 450-550°C and maintained for 20-30 minutes. At the same time, mechanical vibration with a frequency of 25-35Hz and an amplitude of 0.15-0.35mm is applied to further eliminate the residual stress in the weld, especially for the local stress concentration areas that are difficult to eliminate by overall heat treatment. The effect is more significant, reducing the local residual stress to below 80MPa.

[0018] Its working mechanism is as follows: First, pre-treat both sides of the annular seam of the pressure vessel to remove oil, rust impurities and grind to the specified roughness to create good conditions for welding. Then, pre-deform the parent material according to the material, size and design requirements, mechanically pre-bend the thinner plate and pre-stretch the thicker plate, so that the welding deformation and pre-deformation are offset, and the dimensional accuracy and appearance quality are improved. Then, the local area of ​​the annular seam is preheated by an annular heating belt, and the preheating temperature and time are controlled according to the wall thickness to reduce the cooling rate, reduce the hardened structure, and improve the toughness and crack resistance of the weld. Then, select appropriate welding materials according to the material, specification and design pressure, adjust the welding equipment parameters, and ensure arc stability and droplet transition. The welding adopts a multi-layer and multi-pass process. Tungsten inert gas arc welding is used for the base welding to ensure root fusion. When there are multiple layers and multiple passes, adjacent welds are staggered to disrupt the crystallization direction, refine the grains, and improve fatigue resistance and compressive strength. After welding, the weld is covered with insulation cotton to slow down the cooling, and then X-ray inspection is carried out after cooling. The qualified weld is heat treated as a whole to eliminate stress. Then the weld and heat-affected zone are locally induction heated and mechanical vibration is applied to further reduce residual stress, especially in the area of ​​local stress concentration, so as to achieve pressure-resistant welding of the pressure vessel circumferential seam and improve the weld quality and the service life of the pressure vessel.

[0019] Compared with the prior art, the present invention has the following beneficial effects: By adopting the pre-deformation control method of mechanical pre-bending or pre-stretching for plates of different thicknesses, the deformation of the annular seam after welding and the pre-deformation offset each other, effectively reducing the final welding deformation and improving the dimensional accuracy of the pressure vessel.

[0020] Preheating the local area of ​​the pressure vessel's annular seam and accurately controlling the preheating temperature and time according to the wall thickness reduces the cooling rate of the weld joint, reduces the hardened structure in the weld metal, and improves the toughness and crack resistance of the weld.

[0021] On the basis of the composition of conventional low-alloy steel welding rods, specific proportions of nickel, chromium, molybdenum and other elements are added to improve the strength, toughness and corrosion resistance of the weld metal. It can maintain good mechanical properties under high temperature and high pressure environments, effectively extending the service life of the pressure vessel.

[0022] A multi-layer and multi-pass welding process is adopted, and tungsten inert gas arc welding is used for the base welding to ensure complete fusion of the weld root. In multi-layer and multi-pass welding, the two adjacent welds are staggered with a staggered angle of 45°-75°, which disrupts the crystallization direction of the weld, refines the grains, reduces the formation of columnar crystals, and significantly improves the fatigue resistance and compressive strength of the weld, so that when the pressure vessel is subjected to alternating loads, the weld is not prone to fatigue cracks.

[0023] After welding, the weld is covered with insulation cotton for slow cooling and X-ray inspection is carried out. The qualified welds are subjected to overall heat treatment. The pressure vessel is placed in a heat treatment furnace as a whole. The heating speed, heating temperature, insulation time and cooling speed are strictly controlled to reduce the residual stress of the weld to below 100MPa.

[0024] After the overall heat treatment, the weld and heat-affected zone are locally inductively heated and mechanical vibration is applied to further eliminate the residual stress in the weld. This is especially effective for local stress concentration areas that are difficult to eliminate with overall heat treatment, and the local residual stress can be reduced to below 80MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a flow chart of a pressure-resistant welding method for annular seams of pressure vessels. Specific implementation methods

[0026] The technical solutions in the embodiments of the present invention will be fully described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0027] like Figure 1 As shown, a pressure-resistant welding method for annular seams of pressure vessels is characterized by comprising the following steps: S1: Preparation before welding; S2: pre-deformation control; S3: local preheating; S4: Select welding materials; S5: Adjust welding equipment parameters; S6: Post-welding treatment.

[0028] Step S1: Preparation before welding: Pre-treatment is to pre-treat the 20-30mm range on both sides of the annular seam of the pressure vessel to be welded, specifically to remove oil stains and rust impurities on the surface by mechanical grinding, use sandpaper with a particle size of 80-120 mesh, grind until the surface reveals a metallic luster, make the surface roughness reach Ra10-Ra15μm, and wipe with an organic solvent.

[0029] Step S2 pre-deformation control specifically includes pre-deformation treatment of the parent material on both sides of the annular seam according to the material, size and design requirements of the pressure vessel; For thinner plates with a thickness of 10-20mm, a mechanical pre-bending method is used, and the pre-bending curvature is controlled to produce a pre-bending amount of 0.5-1.5mm per meter length; For plates with a thickness of 20-50 mm, the pre-stretching method is adopted, the tensile stress is controlled between 10%-20% of the material yield strength, and the stretching time is 5-10 minutes.

[0030] The local preheating in step S3 is to preheat the local area of ​​the annular seam of the pressure vessel before welding. When the wall thickness is 10-20 mm, the preheating temperature is controlled at 100-150°C; when the wall thickness is 20-50 mm, the preheating temperature is controlled at 150-200°C. The preheating is performed by surrounding the annular seam with an annular heating belt with a width of 50-80 mm. The heating time is set to 15-30 minutes according to the size and thickness of the heating area.

[0031] Step S4 selects welding materials, specifically, according to the material, specification and design pressure requirements of the pressure vessel, selects appropriate welding materials; the impact toughness of the deposited metal at -10°C-10°C is not less than 34J, the carbon content in the chemical composition is 0.12%-0.18%, the manganese content is 1.20%-1.60%, the silicon content is 0.20%-0.50%, and the sulfur and phosphorus contents are not more than 0.035%.

[0032] Step S5 adjusts the welding equipment parameters. Specifically, for manual arc welding, the welding current is set to 140-180A, the welding voltage is set to 24-28V, and the welding speed is controlled at 18-22mm / min according to the welding material and the thickness of the weldment; for gas shielded welding, the wire feeding speed is set to 4-6m / min, and the CO2 gas flow rate is adjusted to 18-22L / min.

[0033] Step S6 post-welding treatment specifically includes covering the weld with insulation cotton with a thickness of 30-50mm, slowly cooling the weld to room temperature, the cooling time is not less than 2 hours, and after cooling to room temperature, the weld is inspected by radiographic inspection, and the weld that passes the inspection is subjected to stress relief treatment. The pressure vessel is placed in a heat treatment furnace as a whole by an overall heat treatment method, and the heating rate is controlled at 30-50℃ / h, and heated to 580-620℃. The insulation time is calculated according to the wall thickness of the container, and the insulation time is 1 hour for every 25mm wall thickness, and the insulation time is not less than 2 hours. Then the pressure vessel is cooled with the furnace, and the cooling rate is controlled at 20-30℃ / h. The residual stress of the weld is reduced to below 100MPa, and the weld surface is polished to reduce the surface roughness of the weld to Ra3.2-Ra6.3μm.

[0034] The welding material is based on the composition of conventional low-alloy steel welding rods, with the addition of 0.8%-1.2% nickel, 0.5%-0.8% chromium and 0.2%-0.4% molybdenum.

[0035] The welding adopts multi-layer and multi-pass welding process, and the base welding adopts tungsten inert gas arc welding. During base welding, the welding current is controlled at 80-100A, the arc voltage is 10-12V, and the welding speed is 8-12mm / min to ensure that the root of the weld is completely fused. The thickness of the base weld is controlled at 3-4mm. During multi-layer and multi-pass welding, the welding directions of the two adjacent layers of welds are staggered with each other, and the staggered angle is 45°-75°.

[0036] After the overall heat treatment, the weld and heat-affected zone are locally induction heated, and the heating temperature is controlled at 450-550°C for 20-30 minutes. At the same time, mechanical vibration with a frequency of 25-35 Hz and an amplitude of 0.15-0.35 mm is applied.

[0037] The following is a specific implementation method of a pressure vessel annular seam pressure-resistant welding method: First, prepare welding materials and various welding and auxiliary equipment that meet the requirements. For the 20-30mm range on both sides of the annular seam of the pressure vessel to be welded, use 80-120 mesh sandpaper to mechanically polish to remove oil and rust until the surface shows metallic luster and the roughness reaches Ra10-Ra15μm, and then wipe it with an organic solvent. Subsequently, pre-deformation control is performed according to the thickness of the plate. The 10-20mm thinner plate is mechanically pre-bent, and the pre-bending amount per meter length is 0.5-1.5mm. The 20-50mm thicker plate adopts a pre-stretching method with a tensile stress of 10%-20% of the material yield strength and a time of 5-10 minutes. Next, for Q345R material containers, a 50-80mm wide annular heating belt is used to heat around the annular seam for 15-30 minutes when the wall thickness is 10-20mm, so that the temperature reaches 100-150℃, and when the wall thickness is 20-50mm, it is heated to 150-200℃. After that, the welding materials are selected according to the material, specification and design pressure. The manual arc welding is set to 140-180A, 24-28V and 18-22mm / min, and the gas shielded welding is set to 4-6m / min and 18-22L / min. The welding adopts multi-layer and multi-pass process, and the tungsten inert gas arc welding is used for the base welding, with a current of 80-100A, an arc voltage of 10-12V, a speed of 8-12mm / min, and a weld thickness of 3-4mm. When multi-layer and multi-pass, the adjacent welds are staggered 45°-75°. After welding, cover the weld with 30-50mm thick insulation cotton and slowly cool for more than 2 hours. After room temperature, perform X-ray inspection. Put the qualified weld into the heat treatment furnace as a whole, heat it to 580-620℃ at 30-50℃ / h, keep it warm for 1 hour and not less than 2 hours for every 25mm wall thickness, and then cool it with the furnace at 20-30℃ / h to reduce the residual stress to below 100MPa. Grind the weld to a roughness of Ra3.2-Ra6.3μm, and finally perform local induction heating at 450-550℃ on the weld and heat-affected zone for 20-30 minutes. At the same time, apply mechanical vibration with a frequency of 25-35Hz and an amplitude of 0.15-0.35mm to reduce the local residual stress to below 80MPa.

Claims

1. A pressure-resistant welding method for annular seams of pressure vessels, characterized in that: The following steps are involved: S1: Preparation before welding; S2: pre-deformation control; S3: local preheating; S4: Select welding materials; S5: Adjust welding equipment parameters; S6: Post-welding treatment.

2. A pressure-resistant welding method for annular seams of pressure vessels according to claim 1, characterized in that: Step S1: Preparation before welding: Pre-treatment is to pre-treat the 20-30mm range on both sides of the annular seam of the pressure vessel to be welded, specifically to remove oil stains and rust impurities on the surface by mechanical grinding, use sandpaper with a particle size of 80-120 mesh, grind until the surface reveals a metallic luster, make the surface roughness reach Ra10-Ra15μm, and wipe with an organic solvent.

3. The pressure-resistant welding method for annular seams of pressure vessels according to claim 1, characterized in that: Step S2 pre-deformation control specifically includes pre-deformation treatment of the parent material on both sides of the annular seam according to the material, size and design requirements of the pressure vessel; For thinner plates with a thickness of 10-20mm, a mechanical pre-bending method is used, and the pre-bending curvature is controlled to produce a pre-bending amount of 0.5-1.5mm per meter length; For plates with a thickness of 20-50 mm, the pre-stretching method is adopted, the tensile stress is controlled between 10%-20% of the material yield strength, and the stretching time is 5-10 minutes.

4. A pressure-resistant welding method for annular seams of pressure vessels according to claim 1, characterized in that: The local preheating in step S3 is to preheat the local area of ​​the annular seam of the pressure vessel before welding. When the wall thickness is 10-20 mm, the preheating temperature is controlled at 100-150°C; when the wall thickness is 20-50 mm, the preheating temperature is controlled at 150-200°C. The preheating is performed by surrounding the annular seam with an annular heating belt with a width of 50-80 mm. The heating time is set to 15-30 minutes according to the size and thickness of the heating area.

5. The pressure-resistant welding method for annular seams of pressure vessels according to claim 1, characterized in that: Step S4: selecting welding materials, specifically, selecting appropriate welding materials according to the material, specification and design pressure requirements of the pressure vessel; The impact toughness of the deposited metal at -10℃-10℃ is not less than 34J. The carbon content in the chemical composition is 0.12%-0.18%, the manganese content is 1.20%-1.60%, the silicon content is 0.20%-0.50%, and the sulfur and phosphorus contents do not exceed 0.035%.

6. The pressure-resistant welding method for annular seams of pressure vessels according to claim 1, characterized in that: Step S5 adjusts the welding equipment parameters. Specifically, for manual arc welding, the welding current is set to 140-180A, the welding voltage is set to 24-28V, and the welding speed is controlled at 18-22mm / min according to the welding material and the thickness of the weldment; for gas shielded welding, the wire feeding speed is set to 4-6m / min, and the CO2 gas flow rate is adjusted to 18-22L / min.

7. The pressure-resistant welding method for annular seams of pressure vessels according to claim 1, characterized in that: Step S6 post-welding treatment specifically includes covering the weld with insulation cotton with a thickness of 30-50mm, slowly cooling the weld to room temperature, the cooling time is not less than 2 hours, and after cooling to room temperature, the weld is inspected by radiographic inspection, and the weld that passes the inspection is subjected to stress relief treatment. The pressure vessel is placed in a heat treatment furnace as a whole by an overall heat treatment method, and the heating rate is controlled at 30-50℃ / h, and heated to 580-620℃. The insulation time is calculated according to the wall thickness of the container, and the insulation time is 1 hour for every 25mm wall thickness, and the insulation time is not less than 2 hours. Then the pressure vessel is cooled with the furnace, and the cooling rate is controlled at 20-30℃ / h. The residual stress of the weld is reduced to below 100MPa, and the weld surface is polished to reduce the surface roughness of the weld to Ra3.2-Ra6.3μm.

8. The pressure-resistant welding method for annular seams of pressure vessels according to claim 1, characterized in that: The welding material is based on the composition of conventional low-alloy steel welding rods, with the addition of 0.8%-1.2% nickel, 0.5%-0.8% chromium and 0.2%-0.4% molybdenum.

9. The pressure-resistant welding method for annular seams of pressure vessels according to claim 1, characterized in that: The welding adopts multi-layer and multi-pass welding process, and the base welding adopts tungsten inert gas arc welding. During base welding, the welding current is controlled at 80-100A, the arc voltage is 10-12V, and the welding speed is 8-12mm / min to ensure that the root of the weld is completely fused. The thickness of the base weld is controlled at 3-4mm. During multi-layer and multi-pass welding, the welding directions of the two adjacent layers of welds are staggered with each other, and the staggered angle is 45°-75°.

10. The pressure-resistant welding method for annular seams of pressure vessels according to claim 1, characterized in that: After the overall heat treatment, the weld and heat-affected zone are locally induction heated, and the heating temperature is controlled at 450-550°C for 20-30 minutes. At the same time, mechanical vibration with a frequency of 25-35 Hz and an amplitude of 0.15-0.35 mm is applied.

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