Chemical pressure vessel circumferential weld stress concentration reinforcement welding process

Abstract

The invention relates to a chemical pressure vessel circumferential weld stress concentration reinforcement welding process which comprises the following specific steps: A, pre-preparation: defect detection and removal, groove processing pretreatment, joint assembly size control and welding material preparation; b, welding implementation, wherein welding implementation comprises back face backing arrangement, front face pulse welding, back face synchronous welding and cover face welding; c, reinforcement and stress relief; D, quality detection; according to the technical scheme, back-gouging-free welding and stress dispersion reinforcement are integrally fused, back-gouging-free, procedure simplification and base metal protection are achieved through cooperation of a gradient ceramic gasket and pulse welding, stress is dispersed through an inner reinforcing structure and an outer reinforcing structure, the reliability of a welding seam is doubly guaranteed, and the welding quality is improved through combination of vacuum plasma cleaning and variable-parameter pulse welding. By means of the post-welding composite stress eliminating technology, welding root forming and overall strength are both considered, and gas-liquid impact and thermal expansion and cold contraction stress in the operation process can be fully resisted.

Description

A welding process for stress concentration reinforcement of circumferential welds in chemical pressure vessels Technical Field

[0001] This invention relates to a welding technology for chemical pressure vessels, and more particularly to a welding process for stress concentration reinforcement of circumferential welds in chemical pressure vessels. Background Technology

[0002] The circumferential weld in a chemical pressure vessel is a core connection point. Cracking accidents often occur due to welding defects, stress concentration, and inadequacies of traditional processes. The commonly used traditional double-sided welding requires multiple processes: "front welding → carbon arc gouging → grinding and finishing → back welding". This is not only inefficient, but the root cleaning process can also damage the base material, increasing the weld defect rate. At the same time, a single welding method cannot take into account both weld root formation and overall strength. Traditional reinforcement only focuses on weld repair and fails to fully resist gas-liquid impact and thermal expansion and contraction stress during operation. Summary of the Invention

[0003] In view of this, the main objective of the present invention is to provide a welding process for stress concentration reinforcement of circumferential welds in chemical pressure vessels. Through this technical solution, root-cleaning-free welding and stress dispersion reinforcement are integrated into a single design. Stress is dispersed through internal and external reinforcement structures, and a combination of vacuum plasma cleaning and variable-parameter pulse welding is used, along with a post-weld composite stress elimination process. This achieves a balance between weld root formation and overall strength, and can fully resist gas-liquid impact and thermal expansion and contraction stress during operation.

[0004] To achieve the above objectives, the technical solution of this invention is implemented as follows: A welding process for stress concentration reinforcement of circumferential welds in chemical pressure vessels, comprising the following steps: A. Preparatory work, including defect detection and removal, beveling pretreatment, joint assembly dimension control, and preparation of welding materials; B. Welding implementation, including backing gasket placement, front pulse welding, back synchronous welding, and capping welding; C. Reinforcement and stress relief, including composite stress relief, internal reinforcement welding, external reinforcement welding, and reinforcing welding; D. Quality inspection, including visual inspection, non-destructive testing, mechanical property testing, and pressure testing.

[0005] As a further technical solution, the defect detection and removal steps in the preparatory process are as follows: using a triple combination of penetrant testing (PT), eddy current testing (ET), and ultrasonic testing (UT), defects in the circumferential weld and the surrounding 50mm area are checked; the defect range is marked, with the marked area extending 5-8mm beyond the defect edge, and the defect is removed by carbon arc gouging at a current of 80-100A and a speed of 5-8cm / min. After layer-by-layer grinding until the metal luster is exposed, the triple combination test confirms that there are no residual defects.

[0006] As a further technical solution, the pre-treatment step of bevel processing in the pre-preparation is as follows: process an asymmetrical U-shaped bevel with a blunt edge, wherein the blunt edge size is 3.5±0.5mm, the bevel angle is 60°±5°, the surface roughness of the inner wall Ra≤1.6μm, the surface roughness of the outer wall Ra≤3.2μm, and set an R2-3mm arc at the bevel transition; first, perform vacuum plasma cleaning on the bevel, with a vacuum degree of 5×10⁻²Pa and a cleaning time of 12±3s, then wipe a 100mm range on both sides of the bevel with anhydrous ethanol, and perform welding within 30 minutes after air drying.

[0007] As a further technical solution, the backing gasket placement steps in the welding process are as follows: install a gradient thermally conductive ceramic gasket, wherein the inner layer of the ceramic gasket has a thermal conductivity ≥85W / (m・K), the outer layer has a thermal conductivity ≤4W / (m・K), and the gasket width is 10-15mm larger than the bevel; apply a 0.25±0.05mm thick high-temperature adhesive to the gasket mating surface, cure it at 120±5℃ for 20±3min, and after curing, the gap between the gasket and the bevel is ≤0.3mm; preheat the gasket to 80-100℃ before welding.

[0008] As a further technical solution, the front pulse welding step in the welding implementation is as follows: using flux-cored wire gas shielded welding, the peak current for the root pass is 280-290A and the base current is 120-130A, the peak current for the fill pass is 290-300A and the base current is 130-140A, and the pulse frequency is 18±2Hz; the shielding gas is an argon-carbon dioxide mixture with a mixing ratio of 85:15 and a gas flow rate of 22±3L / min; the welding speed is 32±3cm / min, the welding torch oscillation amplitude is 1 / 2 of the bevel width, the oscillation frequency is 6±1 times / minute, and the welding torch stays on both sides of the bevel for 0.5-1s. During the welding process, the interpass temperature is controlled at 80-150℃.

[0009] As a further technical solution, the back-side synchronous welding step in the welding process is as follows: the back-side root pass welding is started within 30 minutes after the front-side welding, with a welding current of 190±10A, a welding voltage of 23±1V, and a welding speed of 42±3cm / min; the shielding gas is pure argon, with a gas flow rate of 16±2L / min, the angle between the welding torch and the base material is controlled at 30°-45°, and the weld formation coefficient is controlled at 1.3±0.1.

[0010] As a further technical solution, the composite stress relief step in the reinforcement and stress relief is as follows: After the main weld is completed, a combination of "ultrasonic impact and local low-temperature tempering" is adopted. The ultrasonic impact frequency is 22±3kHz and the power is 300-350W. Each weld is impacted for 4±1min, and the impact covers the weld and a 20mm area on both sides of the weld. The local low-temperature tempering temperature is 210±10℃, the holding time is 1.2±0.3h, the heating rate is ≤100℃ / h, the cooling rate is ≤80℃ / h, and the residual stress after treatment is ≤150MPa.

[0011] As a further technical solution, the internal reinforcement welding step in the reinforcement and stress relief is as follows: eight triangular supports are evenly arranged at the circumferential weld inside the equipment. The material of the triangular supports is the same as that of the pressure vessel base material, with a thickness of 14±2mm and an included angle of 45°±2° between adjacent supports. One end of the triangular support is fully welded to the inner cylinder, with a weld length ≥ 2 / 3 of the support width, and the other end is connected to the bottom plate of the overflow weir by double-sided fillet weld.

[0012] As a further technical solution, the non-destructive testing steps in the quality inspection are as follows: 100% of the welds are subjected to radiographic testing (RT); 100% of the root of the circumferential welds are subjected to ultrasonic testing (UT); 100% of the fillet welds and reinforcement areas are subjected to penetrant testing (PT); after defects are found, they are repaired, and the corresponding non-destructive testing needs to be carried out again after repair.

[0013] As a further technical solution, clean fresh water is used for the water pressure test. The water temperature during the test is ≥5℃, and the test pressure is 1.25 times the design pressure. The pressure increase rate is ≤0.3MPa / min, and the pressure is held for 30min. During the pressure holding period, there is no leakage, deformation, or abnormal noise. The pressure release rate is ≤0.2MPa / min. After the test, the water inside the equipment is cleaned and rust prevention treatment is performed.

[0014] The beneficial effects of adopting the above technical solution are as follows: This technical solution, through a stress concentration reinforcement welding process for circumferential welds in chemical pressure vessels, achieves the following: 1. Integrated design of root-cleaning-free welding and stress dispersion reinforcement. It achieves root-cleaning-free welding through the synergy of gradient ceramic backing and pulse welding, simplifying the process and protecting the base material. Simultaneously, it disperses stress through internal and external reinforcement structures, providing double assurance of weld reliability, thus preventing damage to the base material during welding. 2. Utilizing a combination of vacuum plasma cleaning and variable-parameter pulse welding solves the problems of residual impurities and incomplete root penetration in traditional pretreatment, improving weld fusion quality without increasing the welding defect rate. 3. The post-weld composite stress relief process balances stress relief effectiveness with energy consumption control, adapting to the high-efficiency operation requirements of chemical equipment. The symmetrical arrangement of the reinforcement structures avoids additional stress caused by material differences or uneven stress distribution. Attached Figure Description

[0015] Figure 1 is a schematic diagram of the overall process flow of the present invention.

[0016] Figure 2 is a comparison table of actual test results for embodiments and comparative examples of the present invention. Detailed Implementation

[0017] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0018] The present invention discloses a welding process for stress concentration reinforcement of circumferential welds in chemical pressure vessels, comprising the following steps: A. Preparatory work S1, including defect detection and removal, beveling pretreatment, joint assembly dimension control, and preparation of welding materials; B. Welding execution S2, including backing gasket placement, front pulse welding, back synchronous welding, and capping welding; C. Reinforcement and stress relief S3, including composite stress relief, internal reinforcement welding, external reinforcement welding, and reinforcement welding; D. Quality inspection S4, including visual inspection, non-destructive testing, mechanical property testing, and pressure testing.

[0019] As a further embodiment, the defect detection and removal steps in the preparatory process are as follows: using a triple combination of penetrant testing (PT), eddy current testing (ET), and ultrasonic testing (UT), defects in the circumferential weld and the surrounding 50mm area are checked; the defect range is marked, with the marked area extending 5-8mm beyond the defect edge, and the defects are removed by carbon arc gouging at a current of 80-100A and a speed of 5-8cm / min. After layer-by-layer grinding until the metallic luster is exposed, the triple combination test confirms that there are no residual defects.

[0020] As a further embodiment, the pre-treatment step of beveling in the pre-preparation is as follows: asymmetrical U-shaped bevel with blunt edge is processed, wherein the blunt edge size is 3.5±0.5mm, the bevel angle is 60°±5°, the surface roughness of the inner sidewall Ra≤1.6μm, the surface roughness of the outer sidewall Ra≤3.2μm, and an R2-3mm arc is set at the bevel transition; the bevel is first vacuum plasma cleaned, the vacuum degree is 5×10⁻²Pa, the cleaning time is 12±3s, and then 100mm range on both sides of the bevel is wiped with anhydrous ethanol. Welding is performed within 30min after air drying.

[0021] As a further embodiment, the backing gasket placement steps in the welding process are as follows: install a gradient thermally conductive ceramic gasket, wherein the inner layer of the ceramic gasket has a thermal conductivity ≥85W / (m・K), the outer layer has a thermal conductivity ≤4W / (m・K), and the gasket width is 10-15mm larger than the bevel; apply a 0.25±0.05mm thick high-temperature adhesive to the gasket mating surface, cure it at 120±5℃ for 20±3min, and after curing, the gap between the gasket and the bevel is ≤0.3mm; preheat the gasket to 80-100℃ before welding.

[0022] As a further embodiment, the front pulse welding step in the welding implementation is as follows: using flux-cored wire gas shielded welding, the peak current for the root pass is 280-290A and the base current is 120-130A, the peak current for the fill pass is 290-300A and the base current is 130-140A, and the pulse frequency is 18±2Hz; the shielding gas is an argon-carbon dioxide mixture with a mixing ratio of 85:15 and a gas flow rate of 22±3L / min; the welding speed is 32±3cm / min, the welding torch oscillation amplitude is 1 / 2 of the bevel width, the oscillation frequency is 6±1 times / minute, and the welding torch stays on both sides of the bevel for 0.5-1s on each side; the interpass temperature is controlled at 80-150℃ during the welding process.

[0023] As a further embodiment, the back-side synchronous welding step in the welding process is as follows: the back-side root pass welding is started within 30 minutes after the front-side welding, with a welding current of 190±10A, a welding voltage of 23±1V, and a welding speed of 42±3cm / min; the shielding gas is pure argon, with a gas flow rate of 16±2L / min, the angle between the welding torch and the base material is controlled at 30°-45°, and the weld formation coefficient is controlled at 1.3±0.1.

[0024] As a further embodiment, the composite stress relief step in the reinforcement and stress relief is as follows: After the main weld is completed, a combination of "ultrasonic impact and local low-temperature tempering" is adopted. The ultrasonic impact frequency is 22±3kHz and the power is 300-350W. Each weld is impacted for 4±1min, and the impact covers the weld and a 20mm area on both sides of the weld. The local low-temperature tempering temperature is 210±10℃, the holding time is 1.2±0.3h, the heating rate is ≤100℃ / h, the cooling rate is ≤80℃ / h, and the residual stress after treatment is ≤150MPa.

[0025] As a further embodiment, the internal reinforcement welding step in the reinforcement and stress relief is as follows: eight triangular supports are evenly arranged at the circumferential weld inside the equipment. The material of the triangular supports is the same as that of the pressure vessel base material, with a thickness of 14±2mm and an included angle of 45°±2° between adjacent supports. One end of the triangular support is fully welded to the inner cylinder, with a weld length ≥ 2 / 3 of the support width, and the other end is connected to the bottom plate of the overflow weir by double-sided fillet weld.

[0026] As a further embodiment, the non-destructive testing steps in the quality inspection are as follows: 100% of the welds are subjected to radiographic testing (RT); 100% of the root of the circumferential welds are subjected to ultrasonic testing (UT); 100% of the fillet welds and reinforcement areas are subjected to penetrant testing (PT); after defects are found during inspection, they are repaired, and the corresponding non-destructive testing needs to be carried out again after repair.

[0027] As a further embodiment, a water pressure test was conducted using clean fresh water. The water temperature during the test was ≥5℃, and the test pressure was 1.25 times the design pressure. The pressure increase rate was ≤0.3MPa / min, and the pressure was held for 30 minutes. During the pressure holding period, there was no leakage, deformation, or abnormal noise. The pressure release rate was ≤0.2MPa / min. After the test, the water inside the equipment was cleaned and rust prevention treatment was performed.

[0028] Example 1 of welding a chemical pressure vessel made of 40CrNiMoA material: The specific steps are as follows: I. Pre-treatment S11. Defect detection and removal: For the circumferential weld and the surrounding 50mm area of ​​the 40CrNiMoA chemical pressure vessel, a triple combination of penetrant testing (PT), eddy current testing (ET), and ultrasonic testing (UT) was used. After inspection, a linear defect of approximately 8mm in length was found, with the marked area extending 6mm beyond the defect edge. The defect was then removed by carbon arc gouging at 90A current and 6cm / min speed. Layered grinding was performed until a metallic luster was exposed. A triple combination inspection was conducted again to confirm no residual defects. 2. Beveling pretreatment: An asymmetrical U-shaped bevel with a blunt edge was machined. The blunt edge size was controlled at 3.5mm, the bevel angle at 60°, the inner wall surface roughness Ra=1.2μm, and the outer wall surface roughness Ra=2.8μm. A 2.5mm radius arc was set at the bevel transition. Vacuum plasma cleaning is performed at a vacuum level of 5×10⁻² Pa for 12 seconds. Afterward, the bevel is wiped with anhydrous ethanol for 100mm on both sides. Welding is prepared within 25 minutes of air drying. 3. Joint assembly dimension control: Assemble the 40CrNiMoA inner cylinder and overflow weir base plate as required. The base plate diameter is 3mm larger than the outer diameter of the inner cylinder on one side. The assembly gap is controlled at 0.8mm, ensuring the fillet weld leg height is 6.2mm with a deviation of ±0.5mm. Within the range, stress dispersion grooves are machined on both sides of the weld, with a depth of 6mm and a width of 12mm. The groove opening has an R3mm arc and is fixed with locating pins with a spacing of 280mm. 4. Prepare welding materials: E5015 welding rods and ER50-6 welding wires are selected as welding materials. The welding rods are baked at 380℃ for 2 hours and then transferred to a 150℃ heat preservation barrel. The exposure time in the air is controlled to be 1.5 hours. No re-baking is performed. The welding wires are wiped dry with anhydrous ethanol and the flux core is checked to be intact and undamaged.

[0029] II. Welding Implementation S21. Backing Gasket Installation: Install a gradient thermally conductive ceramic gasket. The inner layer of the ceramic gasket has a thermal conductivity of 90 W / (m·K), and the outer layer has a thermal conductivity of 3.5 W / (m·K). The gasket width is 12 mm larger than the bevel. Apply a 0.25 mm thick high-temperature adhesive to the gasket mating surface and cure it at 120℃ for 20 min. After curing, the gap between the gasket and the bevel is 0.2 mm. Preheat the gasket to 90℃ before welding. 2. Front Pulse Welding: Use flux-cored wire gas shielded welding. The peak current for the root pass is 285 A, and the base current is 125 A. The peak current for the fill pass is 295 A, and the base current is 135 A. The pulse frequency is 18 Hz. The shielding gas is an argon-carbon dioxide mixture with a mixing ratio of 85:15 and a gas flow rate of 22 L / min. The welding speed is... 3. Welding speed: 32cm / min, welding torch oscillation amplitude is 1 / 2 of the bevel width, oscillation frequency is 6 times / min, welding torch stays on each side of the bevel for 0.8s, and the interpass temperature is controlled at 120℃ during welding; 3. Back side synchronous welding: Start back side root welding within 25 minutes after front side welding, welding current 190A, welding voltage 23V, welding speed 42cm / min, shielding gas is pure argon, gas flow rate 16L / min, welding torch angle with base material is controlled at 38°, weld formation coefficient is controlled at 1.3; 4. Cover welding: After grinding back side weld, use submerged arc welding for cover, welding current 320A, voltage 30V, speed 22cm / min, use multi-pass welding, single pass width is controlled at 12mm, weld reinforcement height after cover is 2mm, use angle grinder to grind the edge to form R2.5mm transition fillet.

[0030] III. Reinforcement and Stress Relief S31. Composite Stress Relief: After the main weld is completed, a combination of "ultrasonic impact and local low-temperature tempering" is used. The ultrasonic impact frequency is 22kHz and the power is 320W. Each weld is impacted for 4 minutes, covering the weld and a 20mm area on both sides of the weld. The local low-temperature tempering temperature is 210℃, the holding time is 1.2h, the heating rate is 80℃ / h, and the cooling rate is 70℃ / h. The residual stress after treatment is 130MPa; 2. Internal Reinforcement Welding: Eight triangular supports are evenly arranged at the circumferential weld inside the equipment. The material of the triangular supports is 40CrNiMoA with a thickness of 14mm. m, the included angle between adjacent supports is 45°, one end of the triangular support is fully welded to the inner cylinder, the weld length is 3 / 4 of the support width, and the other end is connected to the overflow weir bottom plate by double-sided fillet weld; 3. External reinforcement welding: At the corresponding position of the weld on the outer wall of the equipment, weld 4 ring connecting plates, the connecting plates are 50mm wide and 10mm thick, and continuous fillet welds are used for welding, the weld leg height is 8mm, and the weld surface is ground flat; 4. Reinforcement welding: Reinforcement welding is carried out within 20 hours after stress relief, the reinforcement area is preheated to 90℃, manual arc welding is used, the current is 150A, the voltage is 23V, the speed is 9cm / min, and the interpass temperature is controlled at 100℃.

[0031] IV. Quality Inspection S41. Visual Inspection: After cleaning the weld surface, visual inspection combined with a 10x magnifying glass was performed. The weld surface was free of defects such as porosity and slag inclusions. The dimensions met the requirements, the weld reinforcement was 2mm, and the weld leg height deviation was ±0.3mm. 2. Non-destructive Testing: 100% of the welds were subjected to radiographic testing (RT), meeting the requirements of GB / T3323 standard Class III. 100% of the root of the circumferential weld was subjected to ultrasonic testing (UT). 100% of the fillet welds and reinforcement areas were subjected to penetrant testing (PT), and no defects were found. 3. Mechanical Property Testing: Three sets of weld samples were taken for testing. The tensile test showed that the tensile strength reached 92% of the parent material; the impact energy of the -20℃ impact test was 30J with a deviation of 3J; and the 180° bending test showed no cracks. All test items were qualified. 4. Pressure test: Clean fresh water was used for the water pressure test. The water temperature during the test was 8℃, the test pressure was 1.25 times the design pressure, the pressure increase rate was 0.25MPa / min, and the pressure was held for 30min. During the pressure holding period, there was no leakage, deformation, or abnormal noise. The pressure release rate was 0.15MPa / min. After the test, the water inside the equipment was cleaned and rust prevention treatment was performed.

[0032] Example 2 of welding for chemical pressure vessels made of 40CrNiMoA material, the specific steps are as follows: I. Preparatory work S11. Defect detection and removal: The circumferential weld and the surrounding 50mm area of ​​the 40CrNiMoA chemical pressure vessel are subjected to triple detection of "penetrating penetration test (PT), eddy current test (ET), and ultrasonic test (UT)". Two point defects were detected, and the ranges exceeding the defect edges by 5mm and 7mm were marked respectively. The defects were removed by carbon arc gouging at 85A current and 5.5cm / min speed. After layer grinding to metallic luster, the triple combined test confirmed that there were no residual defects; 2. Beveling pretreatment: An asymmetrical U-shaped bevel with a blunt edge is processed. The blunt edge size is 3.2mm, the bevel angle is 58°, the inner wall surface roughness Ra=1.4μm, the outer wall surface roughness Ra=3.0μm, and a bevel transition is set. 1. Set a 2mm radius arc and perform vacuum plasma cleaning on the bevel. The vacuum degree is 5×10⁻²Pa and the cleaning time is 10s. Wipe the 100mm range on both sides of the bevel with anhydrous ethanol and weld within 28 minutes after air drying. 2. Joint assembly dimension control: Assemble the inner cylinder and overflow weir base plate of 40CrNiMoA material. The diameter of the base plate is 3.1mm larger than the outer diameter of the inner cylinder on one side. The assembly gap is 0.9mm. The height of the fillet weld leg is 6.5mm with a deviation of ±0.4mm. Process stress dispersion grooves on both sides of the weld with a depth of 5.5mm and a width of 11mm. The groove opening is a 3mm radius arc and the locating pin spacing is 290mm. 3. Prepare welding materials: Select E5015 welding rods and ER50-6 welding wire. After baking the welding rods at 370℃ for 2 hours, transfer them to a 145℃ heat preservation barrel and expose them to air for 1.8 hours. Re-bake once. Wipe the welding wire with anhydrous ethanol and let it dry. The flux core is intact.

[0033] II. Welding Implementation S21. Backing Gasket Installation: Install gradient thermally conductive ceramic gaskets with an inner layer thermal conductivity of 88 W / (m·K) and an outer layer thermal conductivity of 3.8 W / (m·K). The gasket width is 11 mm larger than the bevel. Apply a 0.23 mm thick high-temperature adhesive to the mating surface and cure at 118℃ for 19 min. After curing, the mating gap is 0.25 mm. Preheat the gasket to 85℃ before welding. 2. Front Pulse Welding: Gas shielded welding with flux-cored wire. Peak current for the root pass is 282 A, base current is 122 A, peak current for the fill pass is 292 A, base current is 132 A, pulse frequency is 17 Hz, shielding gas is argon-carbon dioxide (85:15), flow rate is 20 L / min. 1. Welding speed 30cm / min, welding torch oscillation amplitude 1 / 2 of the bevel width, frequency 5 times / min, dwell on both sides 0.6s, interpass temperature 100℃; 2. Back side synchronous welding: start back side root welding 28min after front side welding, current 185A, voltage 22.5V, speed 40cm / min, pure argon gas protection, flow rate 15L / min, welding torch angle with base material 35°, forming coefficient 1.25; 3. Cover welding: after grinding back side weld, submerged arc welding cover, current 300A, voltage 29V, speed 20cm / min, multi-pass welding single pass width 13mm, weld reinforcement height after cover 1.5mm, grinding edge to form R2mm transition radius.

[0034] III. Reinforcement and Stress Relief S31. Composite Stress Relief: Ultrasonic impact frequency 20kHz, power 310W, impact for 3.5min per weld, covering the weld and 20mm on both sides, local low-temperature tempering at 205℃, holding for 1.0h, heating rate 90℃ / h, cooling rate 75℃ / h, residual stress after treatment 140MPa; 2. Internal Reinforcement Welding: 8 triangular supports made of 40CrNiMoA material, 13mm thick, with an included angle of 44° between adjacent supports. °, one end is fully welded to the inner cylinder, the weld length is ≥ 2 / 3 of the support width, and the other end is double-sided fillet welded to the overflow weir bottom plate; 3. External reinforcement welding: 4 annular connecting plates with a width of 49mm and a thickness of 9.8mm, continuous fillet weld with a weld leg height of 8.2mm, and the surface is ground flat; 4. Reinforcing welding: carried out 22 hours after stress relief, preheating the reinforcing area to 85℃, manual arc welding current 145A, voltage 22.5V, speed 8.5cm / min, interpass temperature 90℃.

[0035] IV. Quality Inspection S41. Appearance Inspection: After cleaning, visual inspection combined with a 10x magnifying glass was performed. No defects such as porosity or slag inclusions were found. The weld height was 1.5mm, and the weld leg height deviation was ±0.4mm, which met the requirements. 2. Non-destructive Testing: 100% RT inspection of welds (GB / T3323 standard, Class III qualified), 100% UT inspection of the root of circumferential welds, and 100% PT inspection of fillet welds and reinforcement areas were performed. No defects were found. 3. Mechanical Property Tests: Tensile test of 3 groups of samples showed tensile strength ≥91% of the base material, impact test at -20℃ showed impact energy of 28J with a deviation of 4J, and 180° bending test showed no cracks, which was qualified. 4. Pressure Test: Clean fresh water pressure test was conducted at a water temperature of 6℃. The test pressure was 1.25 times the design pressure, with a pressure increase rate of 0.28MPa / min. The pressure was maintained for 30 minutes without any abnormalities, and the pressure release rate was 0.18MPa / min. After the test, the accumulated water was cleaned and rust prevention treatment was performed.

[0036] Example 3 of welding for chemical pressure vessels made of 40CrNiMoA material, the specific steps are as follows: I. Preparatory work S11. Defect detection and removal: The circumferential weld and the surrounding 50mm area of ​​the 40CrNiMoA chemical pressure vessel are subjected to triple inspection of "PT, ET, UT". No obvious defects were found, and the process proceeds directly to the next step; 2. Beveling pretreatment: An asymmetrical U-shaped bevel with a blunt edge is machined, with a blunt edge size of 3.8mm, a bevel angle of 63°, an inner wall surface roughness Ra=1.5μm, an outer wall surface roughness Ra=3.1μm, and a 3mm radius arc is set at the bevel transition. Vacuum plasma cleaning time 1 4s, vacuum degree 5×10⁻²Pa, welding within 22min after wiping with anhydrous ethanol; 3. Joint assembly dimension control: the inner cylinder and the overflow weir bottom plate are assembled, the bottom plate diameter is 3.2mm larger than the outer diameter of the inner cylinder on one side, the assembly gap is 0.7mm, the fillet weld leg height is 5.8mm, the deviation is ±0.3mm, the stress dispersion groove depth is 6.5mm, the width is 13mm, the groove opening is R3mm arc, and the locating pin spacing is 270mm; 4. Preparatory welding materials: E5015 welding rod and ER50-6 welding wire. The welding rod is baked at 390℃ for 2h and then transferred to a 155℃ heat preservation barrel and exposed to air for 1.2h without re-baking. The welding wire is wiped dry and the flux core is intact.

[0037] II. Welding Implementation S21. Backing Gasket Layout: The inner layer of the gradient thermally conductive ceramic gasket has a thermal conductivity of 92 W / (m·K), and the outer layer has a thermal conductivity of 3.2 W / (m·K). The width is 14 mm larger than the bevel. A 0.27 mm thick high-temperature adhesive is applied to the mating surface and cured at 123℃ for 22 min. The mating gap is 0.28 mm. Preheat to 95℃ before welding. 2. Front Pulse Welding: Peak current for the root pass is 288 A, base current is 128 A, peak current for the fill pass is 298 A, base current is 138 A, pulse frequency is 19 Hz, and shielding gas flow rate is 24 L / min. 1. Welding speed 34cm / min, welding torch oscillation frequency 7 times / min, dwell time on both sides 0.9s, interpass temperature 140℃; 2. Back side synchronous welding: start 23min after front side welding, current 195A, voltage 23.5V, speed 44cm / min, pure argon flow rate 17L / min, welding torch angle with base material 42°, forming coefficient 1.35; 3. Cover welding: submerged arc welding cover current 340A, voltage 31V, speed 24cm / min, multi-pass welding single pass width 14mm, reinforcement height 2.5mm, edge grinding R3mm transition radius.

[0038] III. Reinforcement and Stress Relief S31. Composite Stress Relief: Ultrasonic impact frequency 24kHz, power 340W, impact for 4.5min per weld, local low-temperature tempering at 215℃, holding for 1.4h, heating rate 95℃ / h, cooling rate 78℃ / h, residual stress 135MPa; 2. Internal Reinforcement Welding: Triangular support thickness 15mm, adjacent support angle 46°, other parameters are consistent with Example 1; 3. External Reinforcement Welding: Annular connecting plate width 51mm, thickness 10.3mm, weld leg height 7.8mm, ground smooth; 4. Reinforcing Welding: Performed 18h ​​after stress relief, preheated to 95℃, manual arc welding current 155A, voltage 23.5V, speed 9.5cm / min, interpass temperature 110℃.

[0039] IV. Quality Inspection S41. Appearance Inspection: No defects, weld height 2.5mm, weld leg height deviation ±0.3mm, meets requirements; 2. Non-destructive Testing: No defects were found in any non-destructive tests, meets standards; 3. Mechanical Property Test: Tensile strength of 3 groups of samples ≥93% of the base material, impact energy 31J, deviation 3J, no cracks in bending test, qualified; 4. Pressure Test: Water temperature 7℃, pressurization rate 0.22MPa / min, pressure holding for 30min without abnormalities, depressurization rate 0.16MPa / min, post-test treatment meets requirements.

[0040] Example 1: Welding of a chemical pressure vessel consistent with the three embodiments above; specific steps are as follows: I. Preparatory work S11. Defect detection: Only ultrasonic testing (UT) was used to inspect the circumferential weld area, without PT or ET testing, and without defect marking and precise removal process; 2. Beveling: A common V-shaped beveling was processed (without blunt edges or rounded transitions), simply wiped with anhydrous ethanol, without vacuum plasma cleaning, and welded after air drying for 60 minutes; 3. Assembly and welding materials: Assembly gap ≤ 1.5mm, stress dispersion groove not processed; welding rods baked at 350℃ for 1 hour, heat preservation barrel temperature 120℃, and exposed to air for 3 hours.

[0041] II. Welding Implementation S21. No backing, direct welding; 2. Ordinary gas shielded welding (non-pulsed) is used on the front side, with a current of 260~270A and no clear interpass temperature control; 3. Back side welding is delayed until 40 minutes after front side welding, and the shielding gas flow rate can be adjusted arbitrarily; 4. Manual arc welding is used for the cover surface, with no clear requirements for single pass width and reinforcement height.

[0042] III. Reinforcement and Stress Relief: S3 is only naturally cooled, without ultrasonic impact or low-temperature tempering, and the internal triangular support, external connecting plate, and reinforcing welding are omitted.

[0043] IV. Quality Inspection S41. Visual inspection of appearance, without the aid of a magnifying glass; 2. 50% of welds were inspected by RT, but no UT or PT tests were performed; 3. Only one set of samples underwent tensile testing, and no impact or bending tests were performed; 4. The hydrostatic test was conducted at 1.1 times the design pressure and held for 20 minutes.

[0044] Comparative Example 2 for welding chemical pressure vessels, consistent with the three embodiments above; the specific steps are as follows: I. Preparatory work S11. Defect detection: UT+PT dual inspection based on the embodiment, simple removal of visible defects; 2. Beveling treatment: Process a simple U-shaped bevel (4mm blunt edge, 55° angle), no plasma cleaning, and weld after air drying for 40 minutes; 3. Assembly and welding materials: Assembly gap ≤ 1.2mm, locating pin spacing ≤ 400mm; welding material treatment is the same as conventional standards.

[0045] II. Welding Implementation S21. Use ordinary ceramic backing, no high-temperature adhesive, no preheating; 2. No pulse control for front welding, current 270~280A, interpass temperature left to its own devices; 3. No clear standard for back welding parameters, welding torch angle is arbitrary; 4. For submerged arc welding cover pass, single pass width ≤20mm, excess height not deliberately controlled.

[0046] III. Reinforcement and Stress Relief: S3 undergoes only simple low-temperature tempering (200℃ / 1h), without ultrasonic impact, omitting internal support, and only welding two simple external connecting plates.

[0047] IV. Quality Inspection S41. Visual inspection with a 5x magnifying glass; 2. 100% RT inspection of welds, no UT inspection; 3. Mechanical property tests on 2 groups of samples, only tensile strength was assessed; 4. No strict limits on the rate of pressure increase and decrease in the hydrostatic test.

[0048] Using circumferential welded seams of chemical pressure vessels made of 40CrNiMoA material as test objects, three welded seams from three examples and two comparative examples were selected. Unified tests were conducted on four core dimensions: quality defects, mechanical properties, stress state, and pressure resistance reliability. The test standards referred to relevant national standards for pressure vessels such as GB / T3323 and GB / T150. The results are shown in Figure 2.

[0049] Therefore, the finished product welded using the process described in Example 3 is the best, exhibiting the optimal mechanical properties: the tensile strength to base material ratio reaches 93%, the highest among the three examples; the impact energy at -20℃ is 31J, exceeding the standard requirement (≥27J) by 4J, with a deviation of only 3J, indicating more stable impact toughness; no cracks were found in the 180° bending test, demonstrating excellent plasticity and fully meeting the stringent requirements of chemical pressure vessels for structural strength and impact resistance; the stress state is more stable: after ultrasonic impact and local low-temperature tempering combined treatment, the residual stress is 135MPa, within the standard range of ≤150MPa, and lower than that in Example 2 (140MPa), indicating a more uniform stress distribution and effectively reducing the risk of cracking due to stress concentration during long-term service; outstanding pressure resistance reliability: the deformation in the hydrostatic test is only 0.12mm, the smallest among all test samples, indicating strong overall integrity and sufficient rigidity of the welded structure; no fatigue cracks were found after 1000 fatigue tests, demonstrating better stability under repeated pressure conditions than other examples, making it more suitable for long-term cyclic operation of chemical equipment. The operating environment is suitable for various processes; the process parameters are highly adaptable: the bevel size (3.8mm blunt edge, 63° angle), welding current and voltage (peak pulse filler layer 298A, back welding current 195A), and stress relief parameters (ultrasonic impact frequency 24kHz, low-temperature tempering 215℃ / 1.4h) are all within a reasonable range, ensuring the stability of welding quality without adding extra process difficulty or cost, making it highly operable; the comparative advantages are significant: compared with the two comparative examples, Example 3 is comprehensively superior in defect control, mechanical properties, stress state, and reliability. Comparative example 1 suffers from frequent defects and substandard performance due to simplified inspection and omission of reinforcement, while comparative example 2 suffers from excessive stress and fatigue cracks due to process simplification. Example 3, through a complete process flow and precise parameter control, achieves comprehensive assurance of finished product quality; in summary, the welding process of Example 3 performs best in mechanical properties, stress control, reliability, and process adaptability, making it the best choice for circumferential weld welding of 40CrNiMoA chemical pressure vessels.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention.

Claims

1. A welding process for stress concentration reinforcement of circumferential welds in chemical pressure vessels, characterized in that, The specific steps are as follows: A. Preparatory work, including defect detection and removal, beveling pretreatment, joint assembly dimension control, and preparation of welding materials; B. Welding implementation, including backing gasket placement, front pulse welding, back synchronous welding, and cover welding; C. Reinforcement and stress relief, including composite stress relief, internal reinforcement welding, external reinforcement welding, and reinforcing welding; D. Quality inspection, including visual inspection, non-destructive testing, mechanical property testing, and pressure testing.

2. The stress concentration reinforcement welding process for circumferential welds of chemical pressure vessels according to claim 1, characterized in that, The defect detection and removal steps in the preparatory process are as follows: a triple combination of penetrant testing (PT), eddy current testing (ET), and ultrasonic testing (UT) is used to check for defects in the circumferential weld and the surrounding 50mm area; the defect range is marked, with the marked area extending 5-8mm beyond the defect edge, and the defect is removed by carbon arc gouging at a current of 80-100A and a speed of 5-8cm / min. After layer-by-layer grinding until the metal luster is exposed, the triple combination test confirms that there are no residual defects.

3. The stress concentration reinforcement welding process for circumferential welds of chemical pressure vessels according to claim 1, characterized in that, The pre-treatment steps for beveling in the preliminary preparation are as follows: Asymmetrical U-shaped bevels with blunt edges are machined, wherein the blunt edge size is 3.5±0.5mm, the bevel angle is 60°±5°, the inner wall surface roughness Ra≤1.6μm, the outer wall surface roughness Ra≤3.2μm, and an R2-3mm radius arc is set at the bevel transition; the bevel is first vacuum plasma cleaned, with a vacuum degree of 5×10⁻²Pa and a cleaning time of 12±3s; then, 100mm of both sides of the bevel are wiped with anhydrous ethanol, and welding is performed within 30 minutes after air drying.

4. The stress concentration reinforcement welding process for circumferential welds of chemical pressure vessels according to claim 1, characterized in that, The backing gasket installation steps in the welding process are as follows: install a gradient thermally conductive ceramic gasket, wherein the inner layer of the ceramic gasket has a thermal conductivity ≥85W / (m・K) and the outer layer has a thermal conductivity ≤4W / (m・K), and the gasket width is 10-15mm larger than the bevel; apply a 0.25±0.05mm thick high-temperature adhesive to the gasket mating surface, cure it at 120±5℃ for 20±3min, and after curing, the gap between the gasket and the bevel is ≤0.3mm; preheat the gasket to 80-100℃ before welding.

5. The stress concentration reinforcement welding process for circumferential welds of chemical pressure vessels according to claim 1, characterized in that, The pulse welding steps in the welding process are as follows: using flux-cored wire gas shielded welding, the peak current for the root pass is 280-290A and the base current is 120-130A, and the peak current for the fill pass is 290-300A and the base current is 130-140A, with a pulse frequency of 18±2Hz; the shielding gas is an argon-carbon dioxide mixture with a mixing ratio of 85:15 and a gas flow rate of 22±3L / min; the welding speed is 32±3cm / min, the welding torch oscillation amplitude is 1 / 2 of the bevel width, the oscillation frequency is 6±1 times / minute, and the welding torch stays on both sides of the bevel for 0.5-1s; the interpass temperature is controlled at 80-150℃ during the welding process.

6. The stress concentration reinforcement welding process for circumferential welds of chemical pressure vessels according to claim 1, characterized in that: The back-side synchronous welding steps in the welding process are as follows: start back-side root pass welding within 30 minutes after front-side welding, with welding current of 190±10A, welding voltage of 23±1V, and welding speed of 42±3cm / min; the shielding gas is pure argon with a gas flow rate of 16±2L / min, the angle between the welding torch and the base material is controlled at 30°-45°, and the weld formation coefficient is controlled at 1.3±0.

1.

7. The stress concentration reinforcement welding process for circumferential welds of chemical pressure vessels according to claim 1, characterized in that: The composite stress relief step in the reinforcement and stress relief process is as follows: After the main weld is completed, a combination of "ultrasonic impact and local low-temperature tempering" is used. The ultrasonic impact frequency is 22±3kHz and the power is 300-350W. Each weld is impacted for 4±1min, and the impact covers the weld and a 20mm area on both sides of the weld. The local low-temperature tempering temperature is 210±10℃, the holding time is 1.2±0.3h, the heating rate is ≤100℃ / h, the cooling rate is ≤80℃ / h, and the residual stress after treatment is ≤150MPa.

8. The stress concentration reinforcement welding process for circumferential welds of chemical pressure vessels according to claim 1, characterized in that: The internal reinforcement welding steps in the reinforcement and stress relief are as follows: Eight triangular supports are evenly arranged at the circumferential weld inside the equipment. The material of the triangular supports is the same as that of the pressure vessel base material, with a thickness of 14±2mm and an included angle of 45°±2° between adjacent supports. One end of the triangular support is fully welded to the inner cylinder, with a weld length ≥ 2 / 3 of the support width, and the other end is connected to the bottom plate of the overflow weir by double-sided fillet weld.

9. The stress concentration reinforcement welding process for circumferential welds of chemical pressure vessels according to claim 1, characterized in that: The non-destructive testing steps in the quality inspection are as follows: 100% of the welds are subjected to radiographic testing (RT); 100% of the root of the circumferential welds are subjected to ultrasonic testing (UT); 100% of the fillet welds and reinforcement areas are subjected to penetrant testing (PT); after defects are found, they are repaired, and the corresponding non-destructive testing must be carried out again after repair.

10. The stress concentration reinforcement welding process for circumferential welds of chemical pressure vessels according to claim 1, characterized in that: The pressure test steps in the quality inspection are as follows: a water pressure test is conducted using clean fresh water, with a water temperature ≥5℃ and a test pressure of 1.25 times the design pressure; the pressure increase rate is ≤0.3MPa / min, the pressure is held for 30min, and there is no leakage, deformation, or abnormal noise during the pressure holding period; the pressure release rate is ≤0.2MPa / min, and after the test, the water inside the equipment is cleaned and rust prevention treatment is performed.

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