Protective gas monitoring method in stainless steel water tank girth welding processing box

Abstract

The invention discloses a method for monitoring protective gas in a stainless steel water tank girth welding processing box, which relates to the technical field of protective gas welding and comprises the following steps of: positioning and mounting a detector, monitoring pressure and concentration in an inflation stage, measuring and calculating the alignment precision of an end socket and an inner container barrel body, performing closed-loop regulation and control on pressure and concentration in a welding process, and performing gas pressure maintaining and ending after welding is finished. According to the method, shielding gas is filled into the water tank inner container, based on the theory that the inflation flow is equal to the shielding gas leakage speed under the constant-pressure working condition, the butt joint precision of the sealing head and the inner container barrel body before welding is detected, the sealing head and the inner container barrel body are assisted to complete precise butt joint, and leakage and corrosion hidden dangers caused by butt joint gaps are avoided from the source; through closed-loop linkage control of the concentration and the pressure, accurate maintenance of the concentration of shielding gas in the water tank and dynamic regulation and control of the pressure in the whole welding process are achieved, the anti-oxidation effect is guaranteed, the pressure in the tank is stabilized within the safety threshold range, and the quality and reliability of girth welding of the stainless steel water tank are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of protective gas welding technology, and more specifically, to a method for monitoring the protective gas inside a stainless steel water tank circumferential weld processing box. Background Technology

[0002] When welding the circumferential seam of stainless steel water tanks, if an insert-welding process is used where the end cap is inserted into the inner liner, a gap will exist between the end cap and the inner liner during welding. This gap can lead to crevice corrosion. Furthermore, without protection on the back of the weld, the high temperature during welding can easily cause the stainless steel weld to oxidize with oxygen in the air, reducing its corrosion resistance. This is a fatal flaw for the stainless steel water tank inner liner, which is subjected to high temperature and high pressure for extended periods. If the end cap is directly butted into the inner liner to form a butt joint, and a lining strip is added during assembly, while this avoids gaps between the end cap and the inner liner to some extent, new gaps will still form between the lining strip inside the inner liner and the circumferential weld, leading to crevice corrosion. At the same time, the oxidation problem on the back of the weld is not fundamentally solved.

[0003] To address the issues of gaps and oxidation on the back of the weld during the welding of stainless steel water tank end caps and inner tank, existing processes use tooling to round the end cap while simultaneously introducing the inner tank, achieving a precise alignment between the inner tank and the end cap to form a butt joint. High-purity protective gas is then introduced into the stainless steel water tank to purge air and prevent oxidation on the back of the weld during welding. However, this method requires high precision in the alignment between the stainless steel water tank end caps and the inner tank. Therefore, a method is needed to identify the precise alignment between the stainless steel water tank end caps and the inner tank.

[0004] Furthermore, the risk of welding oxidation can only be effectively avoided when the shielding gas concentration reaches a specific threshold. However, due to the structural limitations of stainless steel water tanks, which cannot be completely sealed, the shielding gas easily circulates with the outside air during welding, causing the shielding gas concentration to change in real time and failing to meet the required concentration during welding. While continuously injecting a large flow of shielding gas throughout the welding process can meet the concentration requirements, it results in significant waste of shielding gas, significantly increasing welding costs. Simultaneously, the strong airflow impact can easily cause defects such as root concavity in the weld, severely affecting welding quality. If a segmented gas supply strategy of pre-filling to meet the standard and then supplementing with a small flow throughout the welding process is adopted, to ensure that the pressure and shielding gas concentration within the water tank remain within safe thresholds throughout the welding process and to avoid the problem of increased internal pressure due to high welding temperatures, it is necessary to rely on real-time monitoring of pressure and concentration data to dynamically adjust the gas flow rate and the opening of the outlet valve, forming a closed-loop control system. Summary of the Invention

[0005] The purpose of this invention is to provide a method for monitoring the protective gas inside the circumferential welding processing box of a stainless steel water tank, thereby solving the above-mentioned technical problems.

[0006] A method for monitoring the protective gas inside a stainless steel water tank circumferential weld processing box, used for welding the stainless steel water tank, characterized by comprising the following steps: S1. Detector Positioning and Installation: Since the protective gas is a gas with a density greater than air, and a replacement method of bottom inflation and top exhaust is adopted, the protective gas concentration detector is installed in the air outlet at the top of the stainless steel water tank processing box to ensure that the protective gas concentration in the box meets the welding requirements; the pressure detector is installed in the key areas near the inner end cap and the inner tank body joint inside the inner liner to capture the impact of welding high temperature on the pressure inside the box in real time. S2. Pressure and Concentration Monitoring During Inflation: Close all other openings, leaving only the bottom inflation port and top outlet open for high-flow inflation; during inflation, the protective gas concentration detector and pressure detector collect and report data in real time; when the protective gas concentration reaches 99.5%, the control system gradually reduces the outlet valve until it is closed, and dynamically adjusts the inflation flow rate based on real-time pressure feedback inside the liner to maintain a constant pressure inside the liner, ensuring that the protective gas concentration is not lower than 99.5%; S3. Calculation of alignment accuracy between the end cap and inner liner: Under constant pressure, the inflation flow rate and the leakage rate of the protective gas remain consistent; inflation flow rate... Satisfy the following formula:

[0007] in, The flow coefficient is based on actual measurements; h is the calculated average circumferential gap width; and d is the inner liner diameter. Due to the pressure difference between the inside and outside of the inner liner, To protect the air density; because Inner liner diameter d, pressure difference between the inside and outside of the inner liner and protective gas density Since all quantities are directly obtainable, the average circumferential gap width h can be estimated using the inflation flow rate formula. h is used to characterize the accuracy of the connection between the end cap and the inner liner. If the calculated average circumferential gap width h is less than or equal to the preset value, the connection accuracy is deemed acceptable, and the subsequent welding process can proceed. If the calculated average circumferential gap width h is greater than the preset value, the connection is deemed unacceptable, and the dimensions of the inner liner and the end cap need to be readjusted before reconnecting. The above testing process is repeated until the calculated average circumferential gap width h meets the acceptance standard. S4. Closed-loop control of pressure and concentration during welding: After welding starts, the high temperature increases the pressure inside the water tank; the pressure detector monitors the pressure inside the tank in real time. When the pressure value approaches the preset safety threshold, the control system automatically increases the opening of the air outlet valve to relieve pressure; during this process, the protective gas concentration detector continuously monitors the concentration change. If the protective gas concentration decreases due to the increased valve opening, the gas flow rate is dynamically adjusted based on the concentration feedback data to ensure that the protective gas concentration inside the tank is never lower than the set threshold, thus avoiding oxidation on the back of the weld. S5. Gas pressure holding and finishing after welding: After the circumferential weld is completed, maintain a small flow of gas and keep the valve slightly open to maintain the stable concentration and pressure of the protective gas in the chamber until the weld area cools to room temperature.

[0008] As a preferred technical solution of the present invention, the protective gas is pure argon. At normal temperature (20°C) and standard atmospheric pressure (101.325 kPa), the density of argon is about 1.37 times that of air, which can realize the gas replacement inside the stainless steel water tank processing box.

[0009] In summary, compared with the prior art, the beneficial effects of the present invention are: This invention proposes a method for monitoring the protective gas inside the stainless steel water tank circumferential welding processing chamber. By injecting protective gas into the inner tank, based on the theory that the gas flow rate equals the leakage rate of the protective gas under constant pressure, the method detects the accuracy of the alignment between the end cap and the inner tank before welding, assisting in achieving precise alignment and preventing welding gap problems caused by misalignment. Simultaneously, real-time monitoring of the protective gas concentration at the outlet ensures a stable and dense protective atmosphere on the back of the weld during the welding process, fundamentally avoiding oxidation problems on the back of the weld. Combined with pressure monitoring near the weld, it effectively prevents the risk of abnormal pressure increases inside the tank caused by high welding temperatures, ensuring the safety of the welding operation. Therefore, through closed-loop linkage control of concentration and pressure, this invention assists in the precise alignment of the end cap and the inner tank, achieving precise maintenance of the protective gas concentration and dynamic control of the pressure throughout the welding process. This ensures both anti-oxidation effect and stabilizes the pressure inside the tank within a safe threshold range, significantly improving the quality and reliability of circumferential welding of stainless steel water tanks. Attached Figure Description

[0010] Figure 1 This is a flowchart illustrating the protective gas monitoring method inside the stainless steel water tank circumferential welding processing box of the present invention. Detailed Implementation

[0011] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments given herein are for illustration and explanation only and are not intended to limit the present invention.

[0012] like Figure 1As shown, a method for monitoring the protective gas inside a stainless steel water tank circumferential welding processing box, used for stainless steel water tank welding, includes the following steps: S1. Detector Positioning and Installation: Since the protective gas is a gas with a density greater than air, and a replacement method of bottom inflation and top exhaust is adopted, the protective gas concentration detector is installed in the air outlet at the top of the stainless steel water tank processing box to ensure that the protective gas concentration in the box meets the welding requirements; the pressure detector is installed in the key areas near the inner end cap and the inner tank body joint inside the inner liner to capture the impact of welding high temperature on the pressure inside the box in real time. S2. Pressure and Concentration Monitoring During Inflation: Close all other openings, leaving only the bottom inflation port and top outlet open for high-flow inflation; during inflation, the protective gas concentration detector and pressure detector collect and report data in real time; when the protective gas concentration reaches 99.5%, the control system gradually reduces the outlet valve until it is closed, and dynamically adjusts the inflation flow rate based on real-time pressure feedback inside the liner to maintain a constant pressure inside the liner, ensuring that the protective gas concentration is not lower than 99.5%; S3. Calculation of alignment accuracy between the end cap and inner liner: Under constant pressure, the inflation flow rate and the leakage rate of the protective gas remain consistent; inflation flow rate... Satisfy the following formula:

[0013] in, The flow coefficient is based on actual measurements; h is the calculated average circumferential gap width; and d is the inner liner diameter. Due to the pressure difference between the inside and outside of the inner liner, To protect the air density; because Inner liner diameter d, pressure difference between the inside and outside of the inner liner and protective gas density Since all quantities are directly obtainable, the average circumferential gap width h can be estimated using the inflation flow rate formula. h is used to characterize the accuracy of the connection between the end cap and the inner liner. If the calculated average circumferential gap width h is less than or equal to the preset value, the connection accuracy is deemed acceptable, and the subsequent welding process can proceed. If the calculated average circumferential gap width h is greater than the preset value, the connection is deemed unacceptable, and the dimensions of the inner liner and the end cap need to be readjusted before reconnecting. The above testing process is repeated until the calculated average circumferential gap width h meets the acceptance standard. S4. Closed-loop control of pressure and concentration during welding: After welding starts, the high temperature increases the pressure inside the water tank; the pressure detector monitors the pressure inside the tank in real time. When the pressure value approaches the preset safety threshold, the control system automatically increases the opening of the air outlet valve to relieve pressure; during this process, the protective gas concentration detector continuously monitors the concentration change. If the protective gas concentration decreases due to the increased valve opening, the gas flow rate is dynamically adjusted based on the concentration feedback data to ensure that the protective gas concentration inside the tank is never lower than the set threshold, thus avoiding oxidation on the back of the weld. S5. Gas pressure holding and finishing after welding: After the circumferential weld is completed, maintain a small flow of gas and keep the valve slightly open to maintain the stable concentration and pressure of the protective gas in the chamber until the weld area cools to room temperature.

[0014] In a preferred embodiment of the present invention, the protective gas is pure argon. At normal temperature (20°C) and standard atmospheric pressure (101.325 kPa), the density of argon is about 1.37 times that of air, which can realize gas replacement inside the stainless steel water tank processing box.

[0015] In this embodiment, for a stainless steel water tank inner liner with a volume of 1000L, a diameter d of 800mm, and a height of 1900mm, the circumferential seam welding operation between the end cap and the inner liner body is carried out. The specific operation and protective gas monitoring process are as follows: The end cap is rounded and then connected to the inner tank. First, close all the openings of the inner tank, leaving only the drain hole at the bottom of the inner tank in the upright position as the argon gas filling port, and the hot water outlet at the top of the inner tank as the gas outlet and pressure relief channel. Argon concentration detectors are placed inside the inner liner near the bottom inflation port to ensure accurate capture of concentration changes from the initial inflation stage to the stable stage; pressure detectors are installed inside the inner liner near the end cap joint to monitor the impact of high welding temperatures on pressure near the weld in real time. Argon gas is injected into the inner liner at a high flow rate of 150-200 L / min through the bottom inflation port. After approximately 25 minutes of inflation, the argon concentration detector indicates a concentration of 99.5%. The control system then gradually reduces and closes the outlet valve. Based on real-time pressure feedback from inside the inner liner, the control system dynamically fine-tunes the inflation flow rate, switching it to 10 L / min to maintain a constant pressure within the inner liner. Since maintaining constant pressure requires a leakage rate comparable to the inflation flow rate, monitoring the inflation flow rate helps determine the alignment accuracy between the end cap and the inner liner.

[0016] Specifically, atmospheric pressure is approximately 0.1 MPa. After argon is introduced, during the air replacement phase, the vent is open, and the absolute pressure inside the inner liner remains approximately equal to the external atmospheric pressure. As the argon concentration reaches 99.5%, the vent is gradually closed, and the inflation flow rate decreases. Therefore, during the testing of the interface docking accuracy, the pressure difference between the inside and outside changes minimally. The pressure is 2 Pa. The gap between the water tank head and the inner tank body is an annular gap with a diameter d of 800 mm. The protective gas is argon, and the argon density is... It is 1.784 kg / m 3 The acceptable standard is set as follows: the calculated average gap width h of the annular joint must not exceed 0.1 mm. Because there are multiple intermittent leaks in the annular joint, the flow fields between these leaks interfere with each other, reducing the effective flow efficiency. Furthermore, the actual fluid has viscosity and will experience friction with the wall surface as it flows through the leaks; therefore, the actual flow rate will inevitably be lower than the theoretical value. The flow coefficient is obtained from multiple calculations. If the value is 0.6, then under constant pressure, when the calculated average gap width h of the annular joint is 0.1 mm, the inflation flow rate is... The leakage rate is equal to the following formula:

[0017] This means that during the testing phase of the connection between the water tank end cap and the inner liner, the air flow rate should not exceed [a certain value]. Only when the air flow rate is reached is the docking accuracy considered acceptable. for less than The connection between the end cap and the inner liner body meets the connection accuracy requirements and can be circumferentially welded. During welding, the temperature of the argon gas inside the inner liner rises from 20℃ to 90℃. This increase in temperature causes a rise in pressure inside the liner, necessitating the opening of the top vent to release pressure. To ensure that the argon gas concentration inside the liner remains above 99.5% while releasing pressure, the control system automatically adjusts the vent valve opening based on real-time pressure data from the pressure detector. During this process, the protective gas concentration detector continuously monitors concentration changes. If the protective gas concentration decreases due to increased valve opening, the system immediately adjusts the inflation flow rate dynamically based on the concentration feedback data to ensure that the protective gas concentration inside the chamber remains above the set threshold, thus preventing oxidation on the back of the weld. By finely adjusting the gas flow rate and the size of the outlet control valve, the concentration detected by the argon concentration detector is always above 99.5%, and the pressure detected by the pressure detector is always within the safe range, providing reliable anti-oxidation protection for the back of the weld and avoiding the safety risks caused by high temperature and pressure rise. After completing the circumferential weld, continue to maintain a small flow of gas and keep the valve slightly open to keep the concentration and pressure of the protective gas in the chamber stable until the weld area cools to room temperature. Then stop the gas supply, remove the testing equipment, and finally achieve safe and oxidation-free welding of the weld.

[0018] It should be understood that the above embodiments are one or more embodiments of the present invention. There are many other embodiments and variations based on the present invention. Any variations and modifications made by those skilled in the art without making pioneering innovations are within the protection scope of the present invention.

Claims

1. A method for monitoring the protective gas inside a stainless steel water tank circumferential weld processing box, characterized in that, Includes the following steps: S1. Positioning and installation of the pressure detector: Install the pressure detector in the key areas near the inner end cap and the inner tank body joint inside the inner liner to capture the impact of welding high temperature on the pressure inside the box in real time. S2. Pressure and Concentration Monitoring During Inflation: Close all other openings, leaving only the bottom inflation port and top outlet open for high-flow inflation; during inflation, the protective gas concentration detector and pressure detector collect and report data in real time; when the protective gas concentration reaches 99.5%, the control system gradually reduces the outlet valve until it is closed, and dynamically adjusts the inflation flow rate based on real-time pressure feedback inside the liner to maintain a constant pressure inside the liner, ensuring that the protective gas concentration is not lower than 99.5%; S3. Calculation of alignment accuracy between the end cap and inner liner: Under constant pressure, the inflation flow rate and the leakage rate of the protective gas remain consistent; inflation flow rate... Satisfy the following formula: in, The flow coefficient is based on actual measurements; h is the calculated average circumferential gap width; and d is the inner liner diameter. Due to the pressure difference between the inside and outside of the inner liner, To protect the air density; because Inner liner diameter d, pressure difference between the inside and outside of the inner liner and protective gas density Since all quantities are directly obtainable, the average circumferential gap width h can be estimated using the inflation flow rate formula. h is used to characterize the accuracy of the connection between the end cap and the inner liner. If the calculated average circumferential gap width h is less than or equal to the preset value, the connection accuracy is deemed acceptable, and the subsequent welding process can proceed. If the calculated average circumferential gap width h is greater than the preset value, the connection is deemed unacceptable, and the specifications and dimensions of the inner liner and the end cap need to be readjusted before reconnecting. The above testing process is repeated until the calculated average circumferential gap width h meets the acceptance standard. S4. Closed-loop control of pressure and concentration during welding process: After welding starts, the pressure detector monitors the pressure inside the chamber in real time. When the pressure value approaches the preset safety threshold, the control system automatically increases the opening of the gas outlet valve to achieve pressure relief. During this process, the protective gas concentration detector continuously monitors the concentration change. If the protective gas concentration decreases due to the increase in valve opening, the gas flow rate is dynamically adjusted according to the concentration feedback data to ensure that the protective gas concentration inside the chamber is never lower than the set threshold. S5. Gas pressure holding and finishing after welding: After the circumferential weld is completed, maintain a small flow of gas and keep the valve slightly open to maintain the stable concentration and pressure of the protective gas in the chamber until the weld area cools to room temperature.

2. The protective gas according to claim 1, characterized in that, The protective gas is argon.

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