A welding method for a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel

Abstract

The application discloses a kind of welding methods of high-strength steel shell and low-strength steel inner shell penetration pipe of jacketed pressure vessel, core step includes: precision pretreatment before welding: size and defect detection, homogenization modification and preheating are carried out to machining bevel; Sequential optimization welding: the sequence of "first inside then outside" and "sectional skip welding" is combined, and prior to pipe side (high-strength steel side) is carried out backing surfacing welding; Strict welding control: the combined process of tungsten argon arc welding backing and electrode arc welding filling is used, interlayer temperature, heat input and weld size are accurately controlled; Timely and effective post-welding treatment: high-temperature post-heat treatment is carried out immediately after welding, or according to the structure constraint degree, choose whole intermediate annealing.The application effectively decomposes and releases welding stress through systematic process combination, inhibits the generation of crack, and significantly improves the welding quality and reliability of jacketed vessel penetration pipe joint.

Description

Technical Field

[0001] This invention belongs to the field of pressure vessel manufacturing technology, and particularly relates to a welding method for a through-hole pipe connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel. Background Technology

[0002] In chemical, energy, and other fields, some reaction equipment (such as gasifiers) employs a double-jacketed shell structure. The inner shell bears the main process medium, while the outer shell forms a jacket space through which cooling medium is introduced to protect the inner shell. Such equipment often has numerous process nozzles penetrating both the inner and outer shells. These nozzles are typically high-strength steel forgings and require welding connections to the inner and outer shells. The inner shell often uses low-strength steel with good processability (such as Q245R), while the outer shell, designed to withstand pressure, typically uses high-strength quenched and tempered steel (such as 13MnNiMoR).

[0003] The welding and manufacturing of this structure faces multiple challenges: 1. Strong structural constraints: The nozzle is welded to the inner and outer shells sequentially. The weld of the first weld creates a rigid constraint on the weld of the subsequent weld, preventing the free release of welding stress, which can easily exceed the limits after accumulation. 2. Significant material differences: The inner and outer shells are made of different materials, with significant differences in their thermal expansion coefficients, thermal conductivity, phase transformation characteristics, and other physicochemical properties, resulting in complex stress structure in the weld zone. 3. Limited welding operation space: The jacket gap is narrow, and through-tube welding can usually only be performed from one side (single-sided welding), making back-side root cleaning impossible and requiring extremely high quality for the root pass weld. 4. Complex residual stress state: Due to the above reasons, complex multi-directional residual tensile stress will form in the weld area, which can easily induce defects such as cold cracking and reheat cracking in the heat-affected zone of high-strength steel or the weld zone of low-strength steel.

[0004] Traditional welding experience for single-layer vessel nozzles cannot be directly applied. Conventional welding processes often neglect the sequence of structural constraints and stress system management. When welding such through-fitting nozzles, large-area, deep cracks frequently occur, leading to multiple reworks and even affecting equipment safety and delivery timelines. Therefore, a systematic welding method is urgently needed to fundamentally control welding stress and deformation, ensuring the welding quality of such critical joints. Summary of the Invention

[0005] (1) Technical problem to be solved: Traditional welding experience cannot be applied to the welding of the through-connector between the high-strength steel outer shell and the low-strength steel inner shell of the jacketed pressure vessel. Moreover, the pressure vessel structure and material itself have strong structural constraints, large material differences, limited welding operation space, and complex residual stress state. The present invention provides a welding method for the through-connector between the high-strength steel outer shell and the low-strength steel inner shell of the jacketed pressure vessel. This method forms a closed-loop process system through precise pre-welding preparation, optimization of welding sequence and strategy, strict process control during welding and timely post-weld treatment. It effectively decomposes and releases welding stress, prevents cracks, and improves the reliability of the joint.

[0006] (2) The technical solution adopted in this invention is as follows: A welding method for a through-hole nozzle connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel, comprising a nozzle, an inner shell, and an outer shell, wherein the high-strength steel nozzle penetrates and connects the inner shell and the outer shell, and the welding method for the nozzle, the inner shell, and the outer shell includes the following steps: S1. Pre-welding preparation: a. Beveling preparation and inspection: Processing the beveling joints connecting the nozzle to the outer and inner shells to ensure the dimensional accuracy of the beveling joints; b. Structural rigidity reinforcement and preheating: Anti-deformation support ribs are installed inside the outer shell and inner shell cylinders and near the weld joint area. The base material inside the pipe and on both sides of the bevel is uniformly preheated within the specified range, and the preheating temperature is not lower than 160℃.

[0007] For the bevels connecting the through-hole pipe to the outer and inner shells, machining (such as boring) should be used as the preferred method to ensure the dimensional accuracy and consistency of the bevel angle, blunt edge, and root radius, avoiding dimensional deviations and surface pits caused by grinding. After machining, a 100% penetrant test (PT) is performed on the bevel surface to ensure that there are no surface defects such as cracks or delamination in the bevel and adjacent base material. At the same time, the Brinell hardness of the base material in the bevel area is randomly checked as a pre-welding benchmark.

[0008] After assembly, measure the circumferential root gap of the bevel. For areas with uneven gaps (especially those with excessively small gaps), use tungsten inert gas welding (GTAW) to build up the weld on the base metal bevel surface on the side with the smaller gap, commonly known as "growing the filler metal". Low-hydrogen welding wire such as H08Mn2SiA or a dedicated GTAW welding wire can be used. After the weld buildup, grind it until it is flush with the overall bevel profile, aiming to make the root gap of the entire bevel uniform, usually controlled at 3-4mm. This step is crucial to avoid local stress concentration caused by uneven filler metal during welding (specific process requirements for the "growing the filler metal": insufficient weld metal will result in an excessively large root gap, and an excessively wide GTAW root pass will lead to low strength, causing bottom cracks under the shrinkage stress of the weld during the later weld filling process; specifically, the current and voltage should be at the lower limit of the standard range, and the welding speed should be at the upper limit of the standard range to ensure the weld strength of the weld metal).

[0009] Inside the cylinder, near the weld joint, temporary support stiffeners (typically 20mm thick) are welded to enhance local rigidity and resist welding deformation. Before welding, an efficient combined preheating method is employed. Preferably, an electric heating rope is wound around a special tooling or a flame heater (with three gas flame nozzles at the end) is used to heat the pipe from inside; simultaneously, electric heating pads are arranged within a 150-200mm range on both sides of the bevel on the outside of the cylinder for auxiliary heating. Uniform preheating is ensured, with a preheating temperature not lower than 160℃, and multi-point temperature monitoring is used. S2. Welding Implementation: a. Welding Sequence: Weld the joint between the nozzle and the inner shell first, then weld the joint between the nozzle and the outer shell; b. Root Pass Welding Strategy: Use TIG welding for single-sided welding with double-sided forming for the root pass; during the root pass, the welding arc should first point towards and melt the edge of the bevel on the nozzle side, forming a 4-6mm weld overlay, before completing the entire circumference; c. Segmented Skip Welding Method: Divide the circumferential weld into at least 3 welding segments, and use a segmented skip welding sequence for the root pass and filler welds. That is, after completing part of the weld in the first segment, skip to the second segment, then the third segment, and so on, until the root pass of each segment is completed; the same skip welding sequence is used for the filler weld, layer by layer; d. Weld Bead and Heat Input Control: Use multi-layer, multi-pass welding, with the thickness of a single weld bead controlled at 2-3mm. Strictly control the heat input during shielded metal arc welding. Interpass temperature should be controlled within the range of 160℃-250℃; heat input should be ≤18.72kJ / cm, specifically adjusted according to the welding elements: current, voltage, and welding speed. e. Interpass cleaning and inspection: After every 2-3 filler passes, perform a visual inspection and thoroughly remove slag and spatter; after the root pass and when the filler pass reaches 1 / 2 thickness, perform penetrant testing (PT).

[0010] Ideally, the welding sequence should be to first weld the nozzle to the inner shell (low-strength steel), and then weld the nozzle to the outer shell (high-strength steel). This results in less constraint during inner shell welding, and stress can be released to some extent through the nozzle. If the outer shell must be welded first due to assembly sequence limitations, the already welded "outer shell-nozzle" assembly must undergo overall intermediate annealing heat treatment (see S3) before welding the inner shell to fully release stress and prevent rigid locking of the inner shell during subsequent welding. TIG welding should be used for single-sided welding with double-sided root pass. At the start of the root pass, the welding arc should be intentionally directed towards and melt the bevel edge of the high-strength steel nozzle side. Continuous welding should be performed on this side to form an initial weld layer ("growth") of approximately 4-6 mm, effectively thickening the bevel on this side. This helps balance the stress distribution in the fusion zone caused by differences in material strength and allows subsequent root pass welds to form on a more uniform bevel. After completing the initial weld on this side, the entire root pass weld should be completed using standard procedures. Divide the entire circumferential weld into at least three equal sections (e.g., three areas representing the 12 o'clock, 4 o'clock, and 8 o'clock positions on a clock). During welding, do not complete a single section continuously; instead, use a segmented, skip-welding method. For example, first weld a root pass of approximately 100mm in section A, then skip to section B and weld 100mm, then skip to section C and weld 100mm; after completing the first round, return to section A to weld the next section, and repeat this cycle until all sections have completed their root passes. Filling and capping welds follow the same skip-welding sequence, layer by layer. This method disperses welding heat input and shrinkage stress in time and space, avoiding localized heat and stress accumulation. Adhere to multi-layer, multi-pass welding. The thickness of each single weld pass should be strictly controlled to 2-3mm, and the width should not be too wide. When using shielded metal arc welding (SMAW) for filling, select an appropriate specification and strictly control the heat input to prevent excessive heat input from causing coarse grains and reduced toughness in the weld and heat-affected zone. The interpass temperature must be strictly controlled between 160℃ and 250℃. After every 2-3 filler weld passes, the machine must be stopped for visual inspection. Use an angle grinder, pneumatic chisel, and other tools to thoroughly remove slag and spatter from the weld surface, especially along the bevel edges, ensuring the metallic luster is exposed and preventing slag inclusions and incomplete fusion. Critical nodes must undergo non-destructive testing: immediately after the root pass, perform a 100% PT (potential bonding) inspection of the root quality; when the filler weld reaches approximately half its thickness, perform another PT inspection to promptly detect any potentially spreading internal defects. S3. Post-weld treatment: Immediately after welding, the weld and heat-affected zone should be subjected to post-heat treatment at a temperature of not less than 300°C for at least 4 hours.

[0011] After welding, the weld must not be allowed to cool rapidly to room temperature. The heating power should be immediately increased to heat the weld and heat-affected zone to at least 300°C and hold for at least 4 hours for post-heat treatment to remove hydrogen and promote hydrogen escape. For joints with particularly complex structures, extremely high constraints, or those welded in the order of outer shell welding as described in S2.a, post-heat treatment alone may be insufficient. After welding (or after outer shell welding and before inner shell welding), the entire equipment must be placed in a furnace for intermediate annealing heat treatment. The recommended intermediate annealing process is as follows: heat to 560±15°C at a rate of ≤70°C / h, hold for 2.5-3 hours, and then cool to below 400°C at a controlled rate of ≤90°C / h before air cooling. This process effectively reduces the peak value of residual welding stress and avoids delayed cracking and stress corrosion cracking.

[0012] (3) Due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. Systematic crack prevention: This invention is not an improvement of a single process parameter, but a systematic design of the entire process from "bevel preparation - welding implementation sequence strategy - welding process control - post-weld treatment", which comprehensively controls the mechanical and metallurgical root causes of crack formation.

[0013] 2. Active stress management: By optimizing the sequence from "inside to outside", mandatory intermediate annealing, segmented skip welding and uniform bevel, etc., we actively intervene and decompose the welding stress field to avoid its adverse superposition.

[0014] 3. Quality traceability and controllability: Pre-welding bevel PT / hardness testing and critical node PT testing during welding have been introduced to ensure the process is knowable and controllable, reducing the blindness of rework.

[0015] 4. High practicality: The method is derived from the summary and refinement of manufacturing experience of actual major products. The specific measures proposed, such as heating tooling and support scheme, effectively solve the problems of preheating and deformation control caused by the limited space of the jacket structure.

[0016] 5. High reliability: Verified through actual engineering applications, the first-pass yield of joints that previously frequently experienced through-cracks has been significantly improved after adopting the method of this invention, which has significantly improved the manufacturing efficiency and service safety of the products.

[0017] 6. This invention addresses the cracking problem caused by structural constraints, material differences, and complex welding stresses when welding through-hole nozzles to dissimilar steels in jacketed structures. The core steps include: precise pre-welding treatment: dimensional and defect inspection, homogenization, and preheating of the machined bevel; optimized welding sequence: employing a combination of "inner-to-outer" and "segmented skip welding" sequences, prioritizing root pass welding on the nozzle side (high-strength steel side); strict in-welding control: using a combination of tungsten inert gas (TIG) welding for the root pass and shielded metal arc welding (SMAW) for the fill pass, precisely controlling interpass temperature, heat input, and weld dimensions; and timely and effective post-weld treatment: immediate high-temperature post-weld heat treatment after welding, or overall intermediate annealing depending on the degree of structural constraints. This invention, through a systematic combination of processes, effectively decomposes and releases welding stress, suppresses crack formation, and significantly improves the welding quality and reliability of through-hole nozzle joints in jacketed containers. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the connection between the connecting pipe and the inner and outer shells of the present invention; Figure 2 This is a schematic diagram of the beveling homogenization treatment described in this invention; Figure 3 The welding sequence expressed in this invention is as follows: first, weld the side closest to the nozzle, allowing the weld to grow first and reducing the weld cracking caused by stress; secondly, it expresses multi-layer, multi-pass welding to reduce stress concentration. Figure 4 This is a schematic diagram of the segmented skip soldering described in this invention; Figure 5 This is a schematic diagram of the tie plate described in this invention (the tie plate has a U-shaped structure). Figure 6 This is the segmented jumper soldering diagram described in this invention; Figure 7 This is a welding diagram of the first-growth-flecked side of the nozzle as described in this invention; Figure 8 It is a physical image of a pressure vessel with nozzles and jacket; Figure 9 This is a schematic diagram of the structure of a flame heater; Figure 10 This is a picture of a flame heater. Figure 11 The ultrasonic spectrum shows that the welding method of this invention produces crack-free welds. Figure 12 It uses ultrasonic patterns obtained from traditional welding with cracks. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] like Figures 1-12 As shown. Figure 1 As shown, a welding method for through-hole nozzles connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel is presented. The distance between the inner and outer shells of the jacketed pressure vessel is 53 mm. Numerous through-hole nozzles need to be welded, such as S9.1-6 and S17.1-6. The outer shell thickness is 60-100 mm, and the inner shell thickness is 40-44 mm. The main welding challenge is preventing welding cracks between the nozzles and the Q245R inner shell.

[0021] Implementation steps: Step 1: Pre-welding preparation (S1) Beveling and Inspection: The original design for the beveling between the nozzle and the outer shell was a machined U-shaped beveling, while the beveling between the nozzle and the inner shell was a V-shaped beveling. In practice, strict machining was performed to ensure precise beveling dimensions (e.g., 38mm width, 2mm blunt edge). After machining, all beveling underwent 100% PT testing to confirm the absence of surface cracks, porosity, etc. The hardness of the base material was measured at approximately 10 evenly distributed points along the beveling edge, and the results were recorded and archived, requiring HBW ≤ 225.

[0022] Beveling homogenization: After assembly, uneven gaps were found in some bevels (such as the S17.3 bevel and the inner shell bevel). An angle grinder was used for initial beveling. For areas with gaps significantly less than 3mm, GTAW welding with φ2.5 H08Mn2SiA welding wire was used for "meat overlay" (or "growth"). Figure 2 (As shown). After welding, carefully grind to ensure the gap around the entire ring is uniformly maintained at 3-4mm. Check the bevel shape again after processing.

[0023] Reinforcement and preheating: On the inner wall of the cylinder, perpendicular to the welding joint, weld three 20mm thick tie plates, firmly spot-welded to the cylinder and the connecting pipe (e.g. Figure 5 To suppress welding deformation. Preheating is done in a combined manner: a frame is fabricated that can be inserted into the pipe, and electric heating rope is wound around it ( Figure 4 Simultaneously, electric heating elements are wrapped around the bevel on both sides of the outer wall of the cylinder within a 200mm radius. The temperature is heated to above 160℃, and an infrared thermometer is used to monitor the temperature at multiple points around the bevel to ensure uniform and compliant temperature.

[0024] Step 2: Welding Implementation (S2) Welding sequence: For the newly established process, the weld between the nozzle and the inner shell (Q245R) is welded first, followed by the weld between the nozzle and the outer shell (13MnNiMoR). However, for some nozzles whose outer shell has already been welded (such as S9.1-6), a subsequent overall intermediate annealing is strictly performed before welding the inner shell.

[0025] Foundation welding strategy and segmented skip welding: Taking the welding of S17.3 nozzle and inner shell as an example.

[0026] GTAW root pass was performed using φ2.5 H08Mn2SiA welding wire.

[0027] First, on the bevel of the 20MnMo pipe side (high-strength steel side), select 2-3 arc initiation points and weld a weld bead approximately 100mm long, so that about 5mm of metal is deposited on this side first (e.g. Figure 2 (Priority welding area).

[0028] like Figure 3 As shown, the entire weld bead is divided into three sections: ①, ②, and ③. A skip-welding method is used: weld a 100mm root pass in section ① → skip to section ② and weld another 100mm → skip to section ③ and weld another 100mm → return to section ① and weld the next 100mm section →... repeat this process twice to complete the root pass.

[0029] Immediately after the root pass, a 100% PT test is performed to confirm that there are no cracks or lack of fusion at the root.

[0030] Filler Welding and Control: For filler welding, J507 welding rods (φ3.2, φ4.0) are used, and the current and voltage are strictly controlled in accordance with the Welding Procedure Specification (WPS).

[0031] Adhere to multi-layer, multi-pass welding: each weld layer should be approximately 2-3 mm thick and no more than 3 times the diameter of the welding rod.

[0032] Temperature control: Use a temperature gauge to monitor the interlayer temperature, maintaining it between 160-250℃. Pause welding when the temperature approaches the lower limit, and resume welding only after heating back to the specified range.

[0033] Continue skip welding: filler welding should still be done according to... Figure 3 The three-stage skip welding sequence is performed, with each layer being welded alternately between the three stages to avoid localized overheating.

[0034] Strict interlayer cleaning: After every two layers of welding, use an angle grinder to thoroughly grind and clean the weld surface to remove all slag and spatter.

[0035] Intermediate inspection: When the weld fills to about 20mm (close to half thickness), perform PT inspection again.

[0036] Step 3: Post-weld treatment (S3) After the entire weld is completed, immediately raise the temperature setting of the electric heating element and the internal heating fixture to 300℃ and start timing. Keep it at that temperature for more than 4 hours and then perform post-heating hydrogen removal treatment.

[0037] For joints like S9.1-6, which have extremely strong structural constraints and whose outer shells have already been welded, the entire equipment was placed in the furnace for intermediate annealing after post-heat treatment. The process curve was as follows: heating at ≤70℃ / h to 560℃, holding at that temperature for 2.5 hours, and then cooling at ≤90℃ / h to 400℃ before being removed from the furnace. Before entering the furnace, a cross-shaped support was installed at the large port of the equipment shell to prevent deformation during heat treatment.

[0038] After post-weld heat treatment and cooling to room temperature, the weld is subjected to 100% ultrasonic testing (UT) and 100% magnetic particle testing (MT) or penetrant testing (PT). The tests show that joints welded using the method of this invention have a significantly improved first-pass yield, and the previously frequent deep crack defects around the entire circumference are effectively controlled.

[0039] The parameters involved in this embodiment include: preheating temperature not lower than 160℃, weld layer thickness of about 2-3mm, and interpass temperature controlled within the range of 160℃-250℃.

[0040] Analysis of the impact of a preheating temperature not lower than 160℃: (1) If it is below this lower limit: Hardened structures and the risk of hydrogen-induced cracking increase dramatically: This is especially true for low-alloy high-strength steels like 13MnNiMoR and 20MnMo forgings, which have high carbon equivalents and a strong tendency to harden. When the cooling rate is too rapid, a hard and brittle martensitic structure easily forms in the heat-affected zone. Hydrogen in the weld cannot escape during rapid cooling and accumulates at micro-defects. Under the combined action of structural stress and welding residual stress, it is highly likely to induce "hydrogen-induced delayed cracking." Case S9.1-6 in the report, where cracking occurred after the initial root pass preheating to only 80℃, is a typical example. Increased welding stress: The low initial temperature of the base metal leads to a greater temperature difference between the high-temperature zone and the surrounding cold metal during welding, resulting in more severe incoordination of thermal expansion and contraction, thus generating greater welding internal stress. Risk of poor fusion: Especially in thick plates and under high restraint conditions, excessively low preheating temperatures may lead to difficulty in arc initiation, poor weld pool fluidity, and an increased risk of root fusion failure.

[0041] (2) If the preheating temperature is too high: Deteriorating welding conditions: Harsh working environment for welders leads to decreased labor productivity and increased susceptibility to fatigue and errors. It can cause the electrode coating to turn red and peel off (for shielded metal arc welding), or disrupt the shielding gas, affecting weld quality. Deterioration of heat-affected zone properties: For quenched and tempered steels (such as 13MnNiMoR), excessive preheating and layer temperatures can cause excessive grain growth in the overheated zone of the heat-affected zone, resulting in decreased impact toughness. Increased total welding heat input exacerbates deformation.

[0042] (3) Considerations for selecting specific values ​​within the range of 160℃-250℃: A temperature bias of 160-180℃ is suitable for applications with relatively low restraint, thinner plates (e.g., a 40mm inner shell), and higher ambient temperatures. This is an economical and efficient choice that meets basic crack prevention requirements. A temperature bias of 200-250℃ is suitable for the following situations: ultra-high restraint joints, where the outer shell is welded first, followed by the inner shell, resulting in extremely high restraint stress; higher carbon equivalent or greater thickness of the base material; and as a safety margin when ambient humidity is high and the diffusible hydrogen content of the welding material is uncertain. During repair welding, the upper limit temperature is typically used to ensure safety.

[0043] Analysis of the impact of controlling the weld thickness to 2-3mm (1) If the weld layer is too thick (e.g., >4-5mm / layer): Excessive single-pass heat input: This results in a large weld pool volume, a long high-temperature residence time, and severe grain coarsening in the weld center and heat-affected zone, leading to a decrease in impact toughness and strength. For 13MnNiMoR quenched and tempered steel, the performance deterioration in the coarse-grained zone is particularly pronounced. Increased welding stress and deformation: Concentrated high heat input generates strong local shrinkage stress, which is detrimental to the uniform distribution of stress along the entire weld length. Insufficient weld pool protection and metallurgical reaction: Thick weld beads may lead to poor gas protection (for GTAW / SAW) and insufficient slag coverage (for SMAW / SAW), easily resulting in porosity and slag inclusions. It also hinders the buoyancy of impurities and the escape of harmful gases from the weld metal. Increased crack susceptibility: Large weld beads cool relatively faster (despite a large total heat input, the cooling rate in the core of a thick weld bead can still be very high), and the coarse microstructure results in poor overall crack resistance.

[0044] (2) If the weld layer is too thin (e.g., <1.5mm): Low production efficiency: Increased number of weld passes significantly increases welding and slag removal time. Excessive reheating of the heat-affected zone: Each weld layer reheats the previous weld and heat-affected zone. Insufficiently thin weld layers cause the heat-affected zone to undergo multiple unfavorable thermal cycles, potentially leading to embrittlement (such as temper embrittlement). Increased susceptibility to defects: Thin weld beads may result in incomplete fusion between layers. Higher requirements for operational stability, making it prone to undercut and poor weld bead formation.

[0045] Analysis of the impact of controlling interlayer temperature between 160℃ and 250℃: (1) If the interpass temperature is below the lower limit (<160℃): This is equivalent to insufficient preheating: when welding subsequent weld passes, the joint has cooled to the "danger temperature zone," with the same effect as low-temperature preheating. The risk of hardening and hydrogen-induced cracking reappears during welding. Many defects in the report are related to this inadequate control. Large temperature fluctuations: This may lead to differences in cooling rates in different areas, causing uneven stress and microstructure.

[0046] (2) If the interpass temperature is higher than the upper limit (>250℃): This is equivalent to the harm of overheating: It damages the quenched and tempered steel base material: When exposed to high temperatures for a long time, the heat-affected zone is repeatedly heated, the grains continue to grow, and the toughness is seriously reduced. This is a major taboo when welding high-strength tempered steel. Welding operation is difficult: Same as overheating. Increased deformation: More heat accumulates overall, and shrinkage deformation is greater. "Reheat cracks" may occur: For some steels with precipitation strengthening elements, if the high temperature stay is too long, reheat cracks may occur in the coarse-grained area of ​​the heat-affected zone.

[0047] Comparative Example: Before the systematic application of the method of this invention, after welding multiple nozzles (such as S9.1-6, S11.1-8, S17.1-6, etc.) to the inner shell on the same equipment, UT inspection revealed a large number of circumferential cracks with a depth of 20-40mm, resulting in an extremely high defect rate and unsatisfactory results from multiple rework attempts. By applying this invention, fundamental problems such as uneven beveling, inadequate preheating, stress concentration, and improper sequence were systematically solved. Subsequent through-hole nozzle welds constructed using this method showed stable quality and a significantly improved flaw detection pass rate, proving the effectiveness and superiority of this invention.

[0048] The above are merely preferred embodiments of the present invention.

Claims

1. A welding method for a through-hole nozzle connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel, comprising a nozzle, an inner shell, and an outer shell, wherein the high-strength steel nozzle penetrates and connects the inner shell and the outer shell, characterized in that, The welding method for the nozzle to the inner shell and the outer shell includes the following steps: S1. Pre-welding preparation: a. Beveling preparation and inspection: Processing the bevels connecting the nozzle to the outer and inner shells to ensure dimensional accuracy. b. Structural rigidity reinforcement and preheating: Anti-deformation support ribs are installed inside the outer shell and inner shell cylinders and near the welded joint area, and the base material inside the nozzle and on both sides of the bevel is uniformly preheated within the specified range, with a preheating temperature of not less than 160℃. S2. Welding Implementation: a. Welding sequence: First weld the joint between the nozzle and the inner shell, then weld the joint between the nozzle and the outer shell; b. Root pass welding strategy: Use tungsten inert gas welding for single-sided welding and double-sided forming root pass; during root pass, the welding arc should first point towards and melt the edge of the bevel on the pipe side to form a 4-6mm weld overlay before completing the entire root pass; c. Segmented skip welding method: Divide the circumferential weld into at least 3 welding segments, and use segmented skip welding sequence for root pass and fill pass welding. That is, after completing part of the weld in the first segment, skip to the second segment, and then the third segment to weld the same part, and so on, until the root pass of each segment is completed; the same skip welding sequence is used for fill pass welding layer by layer. d. Weld bead and heat input control: Multi-layer, multi-pass welding is adopted, with the thickness of a single weld bead controlled at 2-3mm. During shielded metal arc welding, the heat input should be strictly controlled, and the heat input should be ≤18.72kJ / cm. The interpass temperature should be controlled within the range of 160℃-250℃. e. Interlayer cleaning and inspection: After every 2-3 filler welds, remove slag and spatter; perform penetrant testing (PT) after the root pass and when the filler weld reaches 1 / 2 thickness. S3. Post-weld treatment: Immediately after welding, the weld and heat-affected zone should be subjected to post-heat treatment at a temperature of not less than 300°C for at least 4 hours.

2. The welding method for a through-hole pipe connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel according to claim 1, characterized in that, In step S1.b, preheating is performed using an internal heating fixture, which is an electric heating rope or flame heater that can be inserted into the pipe, and is used in conjunction with an electric heating plate wrapped around the bevel of the cylinder.

3. The welding method for a through-hole pipe connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel according to claim 1, characterized in that, Step S1.a further includes performing a 100% penetrant test (PT) on the bevel surface after processing to ensure there are no surface defects; and performing a hardness test on the bevel and the base material on both sides, with HBW≤225.

4. The welding method for a through-hole pipe connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel according to claim 3, characterized in that, Step S1 also includes c: bevel homogenization treatment: detect the bevel assembly gap, control the gap to 3-4mm, for areas with uneven gaps, use tungsten inert gas welding to build up the "meat" on the base material on the side with the relatively smaller gap, and then grind it until it is flush with the overall bevel, so that the final bevel circumferential gap is uniform. The tungsten inert gas welding wire used for "meat building up" is a low-hydrogen type welding wire.

5. The welding method for a through-hole pipe connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel according to claim 1, characterized in that, The high-strength steel connecting pipe is a 20MnMo forging, the low-strength steel inner shell is Q245R, and the high-strength steel outer shell is made of 13MnNiMoR.

6. The welding method for a through-hole pipe connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel according to claim 1, characterized in that, In step S2.c, when performing segmented skip welding, the welding length of each segment is controlled within (100-300mm), specifically 1 / 6 of the pipe circumference.

7. The welding method for a through-hole pipe connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel according to claim 1, characterized in that, In step S2.a, when the structure is limited and the outer shell must be welded first, the completed outer shell weld and the entire connecting pipe are subjected to intermediate annealing heat treatment before welding the inner shell.

8. The welding method for a through-hole pipe connecting a high-strength steel outer shell and a low-strength steel inner shell of a jacketed pressure vessel according to claim 7, characterized in that, The intermediate annealing heat treatment process is as follows: heat to 560±15℃ at a rate of ≤70℃ / h, hold for 2.5-3 hours, and then cool to below 400℃ at a rate of ≤90℃ / h before air cooling.

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