Repair method for correcting recesses of steel storage tank

Abstract

The present application relates to a repair method for correcting the concave of steel storage tank, which utilizes the pressure difference between the inside and outside of the storage tank for preliminary correction; after the whole concave metal storage tank is completely closed, the principle of different pressure difference between the inside and outside and thermal expansion and contraction is utilized, the internal pressure of the storage tank is greater than the external pressure, which acts on the concave area to gradually restore the original state, and the preliminary repair of the steel storage tank is completed; the I-beam is vertically welded on the storage tank wall of the area which is not completely repaired in the preliminary repair, the two ends of the door-shaped frame are respectively welded with the metal storage tank wall on both sides of the I-beam; the mechanical screw jack is placed in the door-shaped frame, and the front end of the piston rod of the mechanical screw jack is welded and fixed with the I-beam; the not completely repaired area is repaired one by one by the mechanical screw jack. The construction material of the present application is easy to obtain, the operation steps are simple, which is helpful to improve the engineering construction quality and construction efficiency.

Description

Technical Field

[0001] The present invention relates to a storage tank construction technology in the petrochemical industry, and in particular to a method for repairing a dent in a steel storage tank used for storing crude oil, chemicals and other products. Background Art

[0002] In emerging coal chemical projects such as coal-to-liquids, coal-to-gas, and their derivative chemicals, large metal storage tank farms carry out transshipment and storage functions, making them indispensable equipment areas within chemical projects. Steel atmospheric pressure dome tanks are widely used in the petrochemical industry. However, improper operation during production or extreme weather conditions leading to sudden temperature fluctuations can cause localized dents in the roof and walls, posing a serious threat to the safe operation of atmospheric pressure tanks. Once a tank has dented, the challenge becomes how to quickly, safely, effectively, and cost-effectively restore it to normal operation. Summary of the Invention

[0003] The purpose of the present invention is to provide a repair method for correcting dents in steel storage tanks, thereby solving the problem of repairing dents in large steel arch storage tanks and improving engineering construction quality and construction efficiency.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a repair method for correcting dents in steel storage tanks, comprising the following steps:

[0005] Step 1: Analyze the cause of steel tank dents and calculate the tank correction pressure;

[0006] Step 2: Install the safety pressure relief device and pressure monitoring device. The safety pressure relief device is used to adjust the pressure in the tank during the correction process, and the pressure monitoring device is used to monitor the pressure in the steel tank.

[0007] Step 3: Initial correction using the pressure difference between the inside and outside of the tank. Once the dented metal tank is completely sealed, the internal pressure is greater than the external pressure by utilizing the pressure difference between the inside and outside and the principle of thermal expansion and contraction. This acts on the dented area to gradually restore it to its original state, completing the initial repair of the steel tank.

[0008] Step 4: Mechanical repair of metal steel storage tanks; erect scaffolding around the tank up to the top floor and prefabricate mechanical correction tooling, which includes an I-beam and a correction assembly consisting of a gantry and a mechanical screw jack; vertically weld the I-beam to the tank wall in the area that was not fully repaired during the initial repair, and weld the two ends of the gantry to the recessed parts of the tank wall on both sides of the I-beam; place the mechanical screw jack inside the gantry and weld the front end of the piston rod of the mechanical screw jack to the I-beam; and perform external pull repairs on the incompletely repaired areas one by one using the mechanical screw jack;

[0009] Step 5: Non-destructive testing of welds in deformed areas of metal steel storage tanks;

[0010] Step 6: Water filling test of metal steel storage tank.

[0011] Furthermore, in step one, the final corrected pressure is calculated based on the on-site environment, weather, day and night temperature difference and design drawings, and the corrected pressure is below the anti-destruction pressure of the metal storage tank.

[0012] Furthermore, in step 2, the safety pressure relief device includes a pressure relief valve; a carbon steel pipe is connected to the emergency vent on the top of the steel storage tank, and the carbon steel pipe is connected to the pressure relief valve.

[0013] Furthermore, in step 2, the pressure monitoring assembly includes a U-shaped glass tube with a pressure scale; a carbon steel pipe is connected to the nitrogen port on the top of the steel storage tank, and one end of the U-shaped glass tube is connected to the carbon steel pipe through a hose.

[0014] Furthermore, in step three, after the metal storage tank is sealed, the safety pressure relief device is controlled according to the observation of the pressure monitoring device. After the tank body is initially repaired, the pressure is stabilized for a period of time, and then the pressure is gradually and slowly reduced to prevent the repaired depressed area from re-depression.

[0015] Furthermore, in step four, a channel steel is welded in the middle of the outer wall of the tank strip plate in the unrepaired area as a reinforcement ring.

[0016] This invention provides a repair process for large steel storage tanks that utilizes an unbalanced pressure differential between the inside and outside of the tank combined with mechanical correction. First, the pressure differential between the inside and outside of the tank is used to restore most of the depressed area. Then, mechanical repair is used to further restore the depressed area to a near-original state. The construction materials are readily available, the operation steps are simple, and it helps improve construction quality and efficiency.

[0017] This method is particularly suitable for correction and repair work under complex conditions such as large temperature changes and severe dents of metal storage tanks. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the safety pressure relief device of the present invention;

[0019] Figure 2 It is a structural schematic diagram of the pressure monitoring device of the present invention;

[0020] Figure 3 It is a schematic diagram of the structure of a U-shaped glass tube;

[0021] Figure 4 It is a schematic diagram of the position of the mechanical correction tool on the wall of the metal storage tank;

[0022] Figure 5 It is a structural diagram of mechanical correction tooling.

[0023] In the figure, 1-tank top connecting flange, 2-safety valve, 3-gate valve, 4-carbon steel pipe, 5-U-shaped glass tube, 6-rubber tube, 7-I-beam, 8-gantry, 9-mechanical screw jack, 10-correction assembly, 11-bracket. DETAILED DESCRIPTION

[0024] The present invention provides a typical embodiment of a method for correcting and repairing a dent in a steel storage tank, which is characterized by comprising the following steps:

[0025] Step 1: Analyze the causes of steel tank dents and calculate the tank correction pressure.

[0026] 1. Analysis of the causes of steel tank dents

[0027] The structure, material, environment, storage medium, operation method, service life and other factors of steel storage tanks all have a certain causal relationship with the dents of storage tanks, and need to be analyzed and demonstrated based on the severity of the dents and the specific circumstances.

[0028] Specifically, according to the "Petrochemical Vertical Cylindrical Steel Welded Storage Tank Design Specifications" and "Vertical Cylindrical Steel Welded Storage Tank Construction Specifications", combined with the actual situation on site, the specific cause of the tank depression was determined.

[0029] 2. Calculation of tank corrected pressure

[0030] The initial correction of dent repair of metal steel dome storage tanks uses the internal and external pressure difference for self-repair, which has a high risk factor. Before the operation, the size of the correction limit pressure must be finally determined based on the corresponding standards and specifications of the steel storage tank, design documents, stress analysis of the tension ring at the connection between the tank top and the tank wall, effective cross-sectional area and other factors through the lower limit of the structural yield strength.

[0031] Step 2: Install the safety pressure relief device and pressure monitoring device.

[0032] The safety pressure relief device is used to adjust the pressure inside the tank during the correction process, and the pressure monitoring device is used to monitor the pressure inside the steel tank.

[0033] During the initial correction phase of a dent repair on a metal steel dome tank, the internal and external pressure differential is utilized for self-healing. A reliable safety pressure relief device is crucial for controlling the pressure differential and preventing secondary accidents. The pressure relief capacity and protective features of the safety pressure relief device should be carefully considered based on factors such as the tank's volume, height, design parameters, repair timeframe, and on-site environment.

[0034] like Figure 1 As shown, the safety pressure relief device includes a pressure relief valve; the pressure relief valve is composed of a safety valve 2 and a gate valve 3, and a carbon steel pipe 4 is connected to the emergency vent on the top of the steel storage tank, and the carbon steel pipe 4 is connected to the pressure relief valve.

[0035] Install a pressure monitoring device in conjunction with the safety pressure relief device to ensure that the pressure is controllable during the initial repair phase. The core of the initial repair phase of a metal steel tank is to use the unbalanced pressure difference between the inside and outside of the tank to repair the metal tank body. The most important monitoring method is to combine the specific design parameters of the tank and the on-site conditions to install relevant devices that can monitor the pressure difference between the inside and outside of the tank. As the pressure difference continues to change, it is monitored and recorded. Used in conjunction with the safety pressure relief device, it ensures that the initial repair pressure meets the corrected pressure requirements calculated in step 2.

[0036] like Figure 2 As shown, the pressure monitoring assembly includes a U-shaped glass tube 5 with a pressure scale ( Figure 3 As shown), water or other liquid is added to the U-shaped glass tube 5; the nitrogen port on the top of the steel storage tank is connected to the carbon steel pipe 4, and one end of the U-shaped glass tube 5 is connected to the carbon steel pipe 4 through a hose 6.

[0037] Step three: Use the pressure difference between the inside and outside of the tank to make preliminary corrections.

[0038] All the sunken metal storage tanks have been sealed. By utilizing the difference in internal and external pressures and the principle of thermal expansion and contraction, the internal pressure of the tank is greater than the external pressure, which acts on the sunken area to gradually restore it to its original state, completing the initial repair of the steel tank.

[0039] After completing technical and on-site preparations for repairing metal steel storage tanks, the specific repair time should be selected based on the characteristics and quantity of the storage medium inside the tank and the on-site weather conditions. Once determined, the appropriate construction personnel, safety precautions, and emergency rescue measures should be prepared. All ancillary holes in the metal storage tank should then be sealed, and the internal pressure of the metal storage tank should be monitored at regular intervals using a pressure monitoring device. The internal pressure of the metal storage tank should be controlled using a safety pressure relief device to ensure that it does not exceed the tank's corrected pressure limit determined in step one. Ultimately, regardless of the state of the dented metal storage tank after repair, the pressure relief device must be immediately opened to ensure internal and external pressure balance, completing the repair using the pressure differential.

[0040] Step 4: Mechanical repair of metal steel storage tanks.

[0041] Scaffolding is erected around the tank, extending to the top floor. After the steel tank is repaired using pressure differential, mechanical repairs are initiated based on the actual situation. Due to the presence of fluid inside the tank and the slow efficiency of internal work, mechanical repairs are considered externally, requiring the erection of scaffolding.

[0042] Prefabricated mechanical straightening fixtures. Based on the actual condition of the metal storage tank after initial repair, the available working space on the scaffolding, and the number of mechanical screw jacks, a sufficient number of matching mechanical straightening fixtures are fabricated and installed using materials such as I-beams and steel plates. The mechanical straightening fixtures consist of I-beams 7 and a straightening assembly 10 consisting of a gantry 8 and mechanical screw jacks 9.

[0043] Based on the initial repair progress of the metal storage tank, the tank wall is divided into sections and reinforced. This involves horizontally welding channel steel to the center of the tank's outer plate in the unrepaired area, creating a reinforcement ring. Mechanical correction and repair are then performed gradually within the divided sections.

[0044] like Figure 4 、 5 As shown, the I-beam 7 is vertically welded to the tank wall in the incompletely repaired area during the initial repair. The ends of the gantry 8 are welded to the pipe walls on both sides of the I-beam 7. A mechanical screw jack 9 is placed inside the gantry 8, and the front end of the piston rod of the mechanical screw jack 9 is welded to the I-beam 7. When welding to the tank wall, care must be taken to ensure the welding current is high to avoid causing secondary damage to the tank wall. The mechanical screw jack 9 then performs pull-out repairs on each of the completed repaired areas.

[0045] By reasonably dividing the repair area, increasing the number of mechanical correction sets, and using the screw jack 9 for repair, the entire divided separate repair area should be dismantled one by one in a planned and partitioned manner to prevent secondary accidents.

[0046] Step 5: Non-destructive testing of welds in the deformed area of ​​the metal steel storage tank.

[0047] After the overall correction is completed, non-destructive testing is performed on the wall panel welds with larger deformation, especially the T-shaped welds to check whether the weld quality meets the requirements.

[0048] Step 6: Water filling test of metal steel storage tank.

[0049] After the non-destructive testing of the repaired metal storage tank is completed, a water test is carried out, and positive and negative pressure tests are performed on the bottom, wall, and roof of the tank according to the design requirements to check whether there is any leakage or deformation in the repaired tank.

[0050] Below 10000m 3 Take a coal tar storage tank, for example. During a water leak test (filling the tank to a depth of 6m), significant temperature fluctuations between day and night caused a large area of ​​denting and deformation in the upper half of the tank's siding. The maximum dent depth reached approximately 600mm, and the siding deformed by 40%. This also caused the spiral staircase to twist. This metal vault tank repair example will be used for further explanation.

[0051] This embodiment mainly illustrates the key construction technologies for initially repairing the tank wall using pressure difference and ultimately mechanically correcting and repairing the tank wall. The remaining construction steps are carried out in accordance with relevant designs, standards and specifications.

[0052] Table 1 Tank design parameters

[0053]

[0054] Table 2 Measurement of tank deformation

[0055] position Maximum deformation (a-generation plate-b-band plate) Deformation area / m² Depth / mm 30° 7-8 57 531 60° 7-8 57 600 120° 7-8 48 496 150° 7-8 84 520 210° 6-8 80 564 240° 8-8 72 466 270° 6-8 80 387 315° 7-8 48 426

[0056] 1. Analysis of the Causes of Coal Tar Storage Tank Depression

[0057] 1. During the preparation for the tank water filling leak test, the staff mistakenly sealed all the existing manholes, cleaning holes and pipe openings, forming a sealed space inside the tank;

[0058] 2. In extreme weather, the temperature changes suddenly at night, resulting in a temperature difference of 18 degrees in a short period of time, forming a large negative pressure inside the tank and exceeding the design value, causing the tank wall to deform inward:

[0059] (1) The tank cleaning hole was closed at around 3:00 PM on April 15, 2022, when the temperature was between 3°C and 20°C. The tank experienced inward deformation in the early morning of April 16, when the temperature was between 2°C and 16°C.

[0060] (2) From the time the tank was closed to the time it deformed internally, the temperature inside the tank changed by about 18°C. At about 3:00 p.m. on April 15, the internal temperature of the tank reached a peak value (20°C), and gradually dropped to a minimum value (2°C) in the early morning of April 16. Due to the isolation of the tank wall and the large volume of air inside, the temperature change inside the tank lagged behind the temperature change outside the tank.

[0061] Table 3 Analysis of pressure difference at construction site

[0062]

[0063] 2. Calculation of Corrected Pressure of Coal Tar Storage Tanks

[0064] 1. The cross-sectional area required for the tension ring at the connection between the top and the wall of the metal storage tank is determined by the following formula:

[0065] Ar=(Pi-0. 00127Dlr / D2)D2×103 / 8[б] tan(θ) = 2044. 21

[0066] Dlr - tank top plate and accessories weight (N), Dl = 0. 00127Dlr / D2 = 0.60862 KPa

[0067] [б] - Allowable stress of material (MPa), take 1 / 1.6 at design temperature, and the lower limit of standard yield strength of material, take 140.63 MPa.

[0068] After calculation, the effective cross-sectional area requirements required for the connection between the tank top and the tank wall are met.

[0069] 2. When the effective area of ​​the tension ring at the connection between the tank top and the tank wall has been determined, the maximum design pressure of the micro internal pressure tank should be determined according to the following formula:

[0070] P=A ReLttanθ / 200 D2 + 0. 00127DLR / D2 = 3. 28117 KPa

[0071] A - effective cross-sectional area of ​​the compression ring at the connection between the tank top and the tank wall (mm 2 )

[0072] Dlr - tank top plate and accessories weight (N), as described above

[0073] ReLt-lower limit of standard yield strength of compression ring material at design temperature (MPa)

[0074] 3. The pressure at which the connection structure between the tank roof and the tank wall produces buckling failure should be determined by the following formula:

[0075] Pf=1.6P—0.000746 Dlr / D2 = 3.70613

[0076] Dlr - Weight of tank top plate and its accessories (N)

[0077] The weight of the edge angle steel is 1538.34kg

[0078] 4. Determination of tank deformation and correction pressure:

[0079] Pj = 3.2 KPa, which is less than the design value of 3.28117 KPa.

[0080] 3. Prepare and install a safety pressure relief device

[0081] Utilize the DN200 emergency vent on the tank top, connect the DN200 carbon steel pipe and supporting valves to the ground, and install a set of safety devices for emergency pressure relief of the tank, and install a protective shed at the ground operation area.

[0082] 4. Manufacturing and installation of pressure monitoring device

[0083] Utilize the DN25 nitrogen port on the top of the storage tank, connect the DN25 carbon steel pipe and the matching valve to 1.5m away from the tank foundation, and combine the reducer, 1 / 4 inch transparent soft rubber tube and U-shaped glass tube 5 to form a U-shaped pressure monitoring device for monitoring. Fix the U-shaped glass tube vertically on the bottom tank wall, and monitor the internal pressure of the storage tank through the corresponding scale value of the U-shaped glass tube 5.

[0084] 5. Metal storage tanks use the pressure difference between the inside and outside of the tank for preliminary correction

[0085] Conduct a final inspection of the coal tar tank roof angle steel, safety pressure relief device, pressure monitoring device, and protective devices. Once all issues are confirmed, begin preliminary corrections. Ensure the pressure relief device is open, and all DN250 material inlets, DN150 material outlets, tank wall manholes, DN25 condensate outlets, and DN50 steam inlets on the tank wall are sealed. Ensure the DN500 light hole in the roof (maintained normally open and closed when pressure is increased), the DN200 radar level gauge port, and the DN300 breathing valve port are sealed with blind plates and gaskets. Use soapy water to test for leaks.

[0086] On May 15, the coal tar storage tank was prepared for pressurization to restore the dented tank wall. At 6:30 a.m., all personnel were in place, and the auxiliary crane and loader were also in place. At 7:00, the top manhole flange was sealed, and at 7:30, the exhaust pressure relief valve at the bottom of the tank was closed. The tank body began to gradually increase pressure under the change of temperature. The pressure increase was strictly controlled by the pressure relief valve. At 7:40, the tank body began to make noises and gradually began to recover. At around 9:00, the tank body recovered to about 90%. The remaining time was in the process of pressure stabilization. The specific records are as follows:

[0087]

[0088] (6) Scaffolding erection

[0089] After the initial repair of the steel storage tank is completed, the outer scaffolding of the tank is erected up to the top floor in accordance with the special construction plan for the tank insulation scaffolding. For the parts that require mechanical repair, the scaffolding structure is appropriately changed in accordance with the actual situation on site to leave enough space for mechanical correction and repair operations.

[0090] (VII) Manufacturing and installation of mechanical correction tools

[0091] Prepare channel steel [12 132m, I-beam 20 96m, 20mm thick steel plate 9m 2 , 10mm thick steel plate 5m 2 Prefabricate the I-beam with reinforcement 7, portal frame 8, and mechanical correction tooling for the reinforcement plate. During the installation process, work is performed in conjunction with the gap between the external scaffolding and the tank to confirm that all welds are fully welded and the weld thickness meets the strength requirements.

[0092] (8) Mechanical correction and repair of metal storage tanks

[0093] The scaffolding outside the coal tar storage tanks was erected by the scaffolding team and passed a three-party inspection. Before the tank wall was straightened, potential stress areas on the tank siding were marked. The materials and welding consumables for welding to the siding were compatible with the siding. A 12# channel steel reinforcement ring was then added to the center of each of the outer walls of tanks 6, 7, and 8, temporarily avoiding any indentations requiring correction. Localized deformation of the siding was then corrected mechanically using a 20T screw jack, a 20# I-beam, a prefabricated straightening fixture for 20mm thick steel plates, and a crane, along with material handling equipment. The straightening was then performed using an external pull method. After the straightening was complete, the reinforcement ring was intermittently welded to the siding (with 100mm gaps between the channel steel welds and 200mm gaps, staggered vertically) to strengthen the tank wall. Welds with significant deformation were then inspected post-correction. The welding current was carefully controlled when welding the straightening fixture to the tank siding to prevent burn-through.

[0094] (9) Nondestructive testing of deformation welds of coal tar storage tanks

[0095] The siding welds with large deformation in coal tar storage tanks were subjected to UT non-destructive testing, especially the T-shaped welds, which passed the X-ray inspection by the NDT company.

[0096] (10) Coal tar storage tank water filling test

[0097] After the mechanical correction of the coal tar storage tank was completed, the tank was subjected to a water test. The test results were normal and met the acceptance standards.

[0098] 1. After the tank bottom is filled with water (designed liquid level 17.22 meters), there is no leakage within 48 hours;

[0099] 2. After the tank wall is filled with water (designed liquid level 17.22 meters), there will be no leakage or abnormal deformation within 48 hours;

[0100] 3. After the tank is filled with water to 16.22m, the tank roof is first subjected to a 2.2KPa positive pressure test. There is no abnormal deformation of the tank roof, and all welds are checked with a foaming agent for leakage. Then the tank roof stability test is carried out with a test pressure of -1.8KPa, and there is no abnormal deformation of the tank.

Claims

1. A method for repairing a dent in a steel storage tank, characterized in that: The following steps are involved: Step 1: Analyze the cause of steel tank dents and calculate the tank correction pressure; Step 2: Install the safety pressure relief device and pressure monitoring device. The safety pressure relief device is used to adjust the pressure in the tank during the correction process, and the pressure monitoring device is used to monitor the pressure in the steel tank. The safety pressure relief device includes a pressure relief valve; a carbon steel pipe is connected to the emergency vent on the top of the steel storage tank, and the carbon steel pipe is connected to the pressure relief valve; The pressure monitoring device includes a U-shaped glass tube with a pressure scale; the nitrogen port on the top of the steel storage tank is connected to a carbon steel pipe, and one end of the U-shaped glass tube is connected to the carbon steel pipe through a hose; Step 3: Initial correction using the pressure difference between the inside and outside of the tank. Once the dented metal tank is completely sealed, the tank body begins to gradually increase pressure as the temperature changes, utilizing the difference in pressure between the inside and outside and the principle of thermal expansion and contraction. The internal pressure of the tank is greater than the external pressure, acting on the dented area to gradually restore it to its original state, completing the initial repair of the steel tank. After the metal storage tank is sealed, the safety pressure relief device is controlled according to the observation of the pressure monitoring device. After the initial repair of the tank body, the pressure is stabilized for a period of time, and then the pressure is gradually and slowly reduced to prevent the repaired dented area from re-denting; Step 4: Mechanical repair of metal steel storage tanks; erect scaffolding around the tank up to the top floor and prefabricate mechanical correction tooling, which includes an I-beam and a correction assembly consisting of a U-shaped frame and a mechanical screw jack; vertically weld the I-beam to the tank wall in the area of ​​the initial repair that was not fully repaired, and weld the two ends of the U-shaped frame to the pipe walls on both sides of the I-beam; place the mechanical screw jack inside the U-shaped frame and weld the front end of the piston rod of the mechanical screw jack to the I-beam; use the mechanical screw jack to pull the repair of the incompletely repaired area one by one; weld a channel steel as a reinforcement ring in the middle of the outer wall of the tank strip plate in the incompletely repaired area; Step 5: Non-destructive testing of welds in deformed areas of metal steel storage tanks; Step 6: Water filling test of metal steel storage tank.

2. The method for repairing a dent in a steel storage tank according to claim 1, characterized in that: In step one, the final corrected pressure is calculated based on the site environment, weather, day and night temperature difference and design drawings. The corrected pressure is below the anti-destruction pressure of the metal storage tank.

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