Full-coverage nondestructive testing method for steel lining welds in underground caverns of compressed air energy storage power plants

Abstract

A full-coverage nondestructive testing method for steel lining welds in underground caverns of compressed air energy storage power plants is presented. [Solution] The method includes the steps of using a low-frequency magnetic inspection method to inspect a steel lining weld for defects and determining the defect depth, and at the same time using a universal calibration test block in the calibration comparison test block to determine the thickness range that can be inspected by the low-frequency magnetic inspection method.If the thickness range that can be inspected covers the thickness of the steel lining to be inspected, the weld inspection work is completed, and if it does not cover the thickness range, proceeding to the next step; pre-treating the surface of the steel lining weld to be inspected and the surface of the adjacent base material to give it a metallic luster; re-confirming the thickness of the steel lining; and using a shear wave ultrasonic inspection method to inspect areas of the steel lining weld that have not been inspected by the low-frequency magnetic inspection method.

Description

[Technical Field]

[0001] The present invention belongs to the technical field of compressed air energy storage, and relates to a full-coverage non-destructive inspection method for steel lining welds of underground caverns in compressed air energy storage power plants. [Background technology]

[0002] China's energy storage industry is experiencing rapid growth as the country advances its new power system. Compressed air energy storage (compressed air) is suitable for large-scale energy storage and is widely used in energy storage applications on both the grid side, the power source side, and the user side. Its applications include peak shifting, frequency regulation, capacity reserve, reactive power compensation, and black start. Currently, compressed air energy storage power plants are primarily built in areas with abundant salt cavern resources, such as Jintan, Jiangsu Province, Yingcheng, Hubei Province, and Feicheng, Shandong Province. While utilizing existing salt cavern resources can significantly reduce construction costs and improve project economics, geographical constraints limit the development of compressed air energy storage, preventing it from meeting the energy storage needs of other regions. To address this issue, the use of artificial underground gas storage (underground caverns) is becoming the mainstream option for large-scale compressed air energy storage power plants.

[0003] The steel flexible sealing layer (steel lining) is an important component of underground caverns. It is located inside the underground cavern, containing compressed air, and surrounded by a secondary concrete lining, primary support, and surrounding rock, and plays important roles in cavity sealing and structural stress transmission. Therefore, the structural integrity and long-term operational reliability of the steel lining are extremely important. The steel lining for underground caverns in compressed air energy storage power plants is typically formed by assembling and welding multiple thin-walled curved steel plates on-site. High-strength carbon steel or low-alloy steel is generally selected for its excellent fatigue resistance. Depending on the gas storage capacity, the weld length can reach thousands or even tens of thousands of meters. Due to structural constraints of the underground cavern, the steel lining must be formed on both sides by single-sided welding from the inside, and multiple welding positions, such as downward welding, vertical welding, and upward welding, may be used. This poses certain challenges in on-site welding and welding quality control, and also poses new challenges in steel lining inspection. In addition, energy storage systems have high requirements for the cleanliness of the compressed air in the gas storage tank and steel lining. If the required cleanliness is not met, it may have a negative impact on equipment such as expansion devices during the energy release stage due to expansion. Therefore, when inspecting steel linings, it is necessary to ensure that no new impurities that are difficult to treat are generated and that no secondary contamination is caused.

[0004] To date, researchers have not yet proposed a specialized, systematic inspection method for steel lining welds in underground caverns for compressed air energy storage power plants. Because their structure is similar to that of flat-plate butt welds, it is easy to imagine that inspection methods for flat-plate butt welds could be used for inspection. Surface magnetic particle or penetrant inspection, or internal ultrasonic inspection methods are commonly used. However, while conventional surface inspection techniques such as magnetic particle and penetrant inspection can intuitively visualize surface defects, they are limited to inspecting defects that are open to the surface or buried defects up to approximately 1 mm below the surface. Furthermore, the reagents used in these inspections, such as contrast enhancement agents, magnetic suspensions, penetrants, and cleaning agents, may cause secondary contamination and are therefore not suitable for direct application to steel lining inspection. Furthermore, the existing ultrasonic inspection standard (NB / T47013.3-2015) stipulates that ultrasonic testing can only be applied to plate materials with a thickness of 6 mm or more. However, the steel linings of underground caverns currently used in compressed air energy storage power plants are only 4 mm thick, making the existing standard inapplicable. Furthermore, conventional ultrasonic testing often uses oil-based binders, which also poses the risk of secondary contamination. As described above, conventional methods have a blind spot in the inspection of welds on thin-walled steel plates of 6 mm or less (the standard cannot be applied), and on the other hand, there is a risk of secondary contamination, making research into new inspection methods urgently needed. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to solve the problem of inspecting the structural integrity of steel lining welds in underground caverns of compressed air energy storage power plants, and to provide a full-coverage non-destructive inspection method for steel lining welds in underground caverns of compressed air energy storage power plants, which has the characteristics of intuitive inspection results and high inspection sensitivity, and can realize high-sensitivity and full-coverage inspection of welds. [Means for solving the problem]

[0006] The technical solution adopted by the present invention is a full-coverage non-destructive testing method for steel lining welds in underground caverns of compressed air energy storage power plants, specifically: Step 1: Use a low-frequency magnetic inspection method to inspect the steel lining weld for defects and determine the defect depth. At the same time, use a general-purpose calibration test block in the calibration comparison test block to determine the inspectable thickness range of the low-frequency magnetic inspection method. If the inspectable thickness range covers the thickness of the steel lining to be inspected, the weld inspection work is completed. If it does not cover the thickness, proceed to step 2. Step 2: Pretreating the surface of the steel lining weld to be inspected and the surface of the adjacent base material to give it a metallic luster; Step 3: Recheck the thickness of the steel lining; Step 4 is to use a shear wave ultrasonic inspection method to inspect the steel lining weld area not inspected by the low frequency magnetic inspection method in step 1.

[0007] In the present invention, further, Step 1, specifically, Step 1.1: determining the testable thickness range of the low-frequency magnetic inspection method using a universal calibration test block in a calibration comparison test block; Defect inspection is carried out using a low-frequency magnetic flaw detector, specifically: Step 1.2: Affix the defect indicator film to the inner surface of the steel lining to be inspected, place the yoke across both sides of the weld, and inspect it in sequence using a crisscross method. The coverage area of ​​the two inspections must overlap by at least 10% during the movement to ensure no inspections are missed. Then, energize and magnetize the film, and continuously observe any changes on the indicator film. After the magnetic particle pattern appears on the defect indicator film, change the magnetic field application angle by at least two degrees, select the angle where the defect indication is more obvious, take and save a photograph on site, and mark the position of the magnetic particle pattern (step 1.3); Step 1.4: Quantifying defect depth using a depth comparison test block and a calibration comparison test block and step 1.5, which grades the inspection results for the steel lining weld.

[0008] Regarding the specific structure of the calibration comparison test block, The calibration comparison test block includes a set of general-purpose calibration test blocks and one depth comparison test block. The general-purpose calibration test block consists of 15 test pieces with a thickness interval of 1 mm, the thinnest test piece being 1 mm thick and the thickest test piece being 15 mm thick. The surfaces of the test pieces are provided with three circular grooves of different depths and three regular cross-shaped grooves of different depths, the depths of the circular grooves being 7 μm, 15 μm, and 30 μm, respectively. The two straight lines of the regular cross-shaped grooves are both 6 mm long and have depths of 7 μm, 15 μm, and 30 μm, respectively. The depth comparison test block is an oblique wedge-shaped test block with a length of 150 mm and a thickness of 15 mm, a flat top, and a sloped bottom. The edge of the flat top is marked with a 150 mm scale. The sloped bottom surface is provided with three uniformly distributed linear grooves of different depths, the depths of the grooves being 7 μm, 15 μm, and 30 μm, respectively.

[0009] In step 1.1, the specific steps for determining the testable thickness range of the low-frequency magnetic inspection method using a universal calibration test block are as follows: Select a test piece from the universal calibration test block, and the thickness of the test piece is the same as that of the thin-walled steel member to be measured, or the thickness of the test piece is closest to and greater than that of the thin-walled steel member. Then, attach a defect indicator film to the non-grooved surface of the test piece; Adjust the pulse frequency of the yoke-type low-frequency magnetic flaw detector to 50Hz, place the yoke on the non-grooved surface, and start the flaw detector. If the pulse frequency value can be adjusted until a magnetic particle pattern appears on the indicator film on the calibration test piece, it indicates that the thickness range that can be inspected by low-frequency magnetic testing covers the thickness of the steel lining to be inspected; If the magnetic particle pattern does not appear throughout, other calibration test pieces thinner than the thickness of the steel lining to be measured may be used to perform tests in order of decreasing thickness until the magnetic particle pattern appears, and the maximum thickness D of the test piece at which the magnetic particle pattern can be displayed may be used as the maximum inspection depth of the low-frequency magnetic test.

[0010] In step 1.4, the specific steps for quantifying defect depth using a depth comparison test block are as follows: After determining the location of the defect magnetic powder pattern, the pulse frequency of the low-frequency magnetic flaw detector may be gradually increased until the defect magnetic powder pattern just disappears, and at this time the parameters of the equipment may be locked, the defect indication film may be attached to the non-grooved surface of the depth comparison test block, the yoke may be placed on the non-grooved surface, the inspection equipment may be restarted, the indicated length of the magnetic powder pattern on the surface may be observed, the corresponding defect depth may be read by comparing it with the scale, and the depth of the inspected defect may be determined.

[0011] Step 4 specifically involves: Using the CSK-IA test block, the first step is to simultaneously find the highest reflected waves of the Φ50mm and Φ100mm arcs through the ultrasonic inspection equipment's specific adjustment program, measure the distance to the front edge of the probe, and then input it into the equipment. In the second step, find the highest wave of the Φ50mm stepped hole with a depth of 30mm and input it into the instrument to determine the actual K value of the probe (step 4.1); Step 4.2: Draw a DAC curve using an ultrasonic test block and create reference points or lines. Step 4.3: Add water as a binder to the polished areas on both sides of the weld to be inspected. Select the DAC curve created by the first channel and perform a 4 dB coupling correction. Adjust the reflection amplitude of the 2 mm deep horizontal through hole to 80% or more of the full screen. Place the ultrasonic probe on the polished area and perform a zigzag scan at a scan speed of 150 mm / s or less. During the scan, monitor the waveform changes on the oscilloscope screen in real time and focus on observing one or three reflected echoes in the TD range of the root of the weld. After scanning on one side, repeat the scan on the other side to ensure full coverage of the weld. If the reflected echo is detected to exceed the DAC curve, the defect location information should be reconfirmed at least on both sides of the weld at multiple angles. If the defect is inside the weld seam, the length should be measured using the -6 dB method, and the information on the side with the longer length should be recorded. The depth, length, position and amplitude of the defect should be recorded. Step 4.4: mark the position on the surface of the seam, and if the inspected defect is within the root position of the weld, call up the reference point or reference line of the second channel, compare the waveform and reflection equivalent, and determine the nature and size of the defect; The steel lining weld may be inspected, graded, and quality evaluated according to step 4.5.

[0012] In step 4.2, the specific structure of the ultrasonic inspection comparison test block is The ultrasonic inspection comparative test block consists of three parts, which are a horizontal through-hole region located in the middle, a first stepped groove region located at both ends, and a second stepped groove region, In the horizontal through-hole area, six horizontal through-holes are distributed in order from top to bottom, the horizontal spacing between each horizontal through-hole is ≥ 15mm, the vertical spacing is 3mm, the distance between the top horizontal through-hole and the top surface of the ultrasonic inspection comparative test block is 3mm, and the distance between the bottom horizontal through-hole and the bottom surface of the ultrasonic inspection comparative test block is 2mm; The first stepped groove region includes six layers of steps, the height of each step differing by 3 mm, and the height of the step located at the end is 3 mm; The second stepped groove region includes seven layers of steps, the height of each step differing by 3 mm, and the height of the step located at the edge is 2 mm; A groove 0.1 mm wide and 1 mm deep may be provided across the width of the ultrasonic inspection comparison test block at the center of the step.

[0013] Step 4.2, specifically: A first channel is selected by an adjustment program specific to the ultrasonic inspection device, and according to the thickness of the steel lining, all of the horizontal through holes whose depth is greater than the thickness of the steel lining and closest to the thickness of the steel lining are selected to create a DAC curve, and the DAC curve is used as a comparison curve; Alternatively, a second channel may be selected separately, and a groove depth equal to the thickness of the steel lining to be inspected or two groove depths closest to that depth may be selected as reference points or reference lines.

[0014] In step 4.4, the specific grading criteria are: 1) If the nature of the defect is qualitatively determined to be crack, lack of fusion, or incomplete penetration, it will be judged as a reject. 2) If the reflection equivalent of the defect exceeds the DAC curve, it is an over-criteria defect and is judged as a failure; and If the defect reflection equivalent does not exceed the DAC curve, a. If the length of a single defect is greater than or equal to the plate thickness, it is judged as unacceptable. b. If the length of a single defect is less than the plate thickness, it may be determined to be a recordable defect and be judged as pass.

[0015] The beneficial effects of the present invention are as follows: The method of the present invention addresses the characteristics and requirements of steel linings in underground caverns of compressed air energy storage power plants, such as thin steel plate thickness, invisible outer walls, long welds, and no contamination during inspection, while also fully considering factors such as efficiency, sensitivity, and economy of non-destructive testing. The method of the present invention uses low-frequency magnetic testing to inspect the steel lining welds, and employs a self-made calibration comparison test block for calibration and defect depth determination during the inspection process. This enables a single full-coverage inspection of thin-walled steel linings (generally less than 8 mm), with a simple inspection procedure and intuitive understanding of the inspection results. For relatively thick steel linings (greater than 8 mm), full-coverage inspection of the welds is achieved by using low-frequency magnetic testing as the basis and shear wave ultrasonic testing as a supplementary method. The method of the present invention makes full use of the characteristics and advantages of the above two inspection methods, has high process compatibility, high sensitivity, and good inspection effect, can fully ensure the welding quality of steel lining, and does not generate pollution throughout the entire inspection process. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a flow chart of the method of the present invention. [Figure 2] 1 is a schematic diagram of the structure of a single universal calibration test strip in a calibration comparison test block used in the method of the present invention. [Figure 3] FIG. 10 is a top view of a depth comparison test block in a calibration comparison test block used in the method of the present invention. [Figure 4] FIG. 1 is a side view of a depth comparison test block in a calibration comparison test block used in the method of the present invention. [Figure 5] 1 is a structural schematic diagram of a groove on the slope of a depth comparison test block in a calibration comparison test block used in the method of the present invention. [Figure 6] 1 is a structural schematic diagram of an ultrasonic inspection comparative test block used in the method of the present invention. FIG. [Figure 7]FIG. 1 is a top view of an ultrasonic inspection comparison test block used in the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

[0018] [Embodiment 1] The full-coverage (entire area) non-destructive inspection method of the present invention for steel lining welds in underground cavities of compressed air energy storage power plants is specifically carried out according to the following steps 1 to 4, as shown in FIG. 1.

[0019] Step 1: Use low-frequency magnetic inspection method to inspect the steel lining weld for defects and determine the defect depth.

[0020] The principle of low-frequency magnetic testing is as follows: Low-frequency magnetic flaw detectors magnetize the yoke using the principles of DC pulse current phase adjustment and frequency conversion. Because they are driven by DC pulse current, the instantaneous start-up impulse and magnetizing current are large, and the generated magnetic flux is more than ten times that of conventional commercial frequency (50Hz) AC magnetic field flaw detectors. By generating different pulse widths at different magnetizing frequencies, the equipment consumes the least amount of power while maximizing flaw detection sensitivity.

[0021] The inspection is carried out using a low-frequency magnetic flaw detector, and the specific process parameter requirements are as follows:

[0022] (1) Magnetization method: yoke method, magnetic pole spacing range: 75 to 200 mm. (2) Type and parameters of magnetizing current: DC pulse current, pulse frequency range: 0 <f≦50Hz。 (3) Lifting force: ≥ 177N. (4) Type of test block: Homemade calibration comparison test block for low-frequency magnetic testing. (5) Magnetic particle pattern display medium: defect display film. (6) Magnetization time: 1~3s.

[0023] The structure of the homemade calibration and comparison test block for low-frequency magnetic testing, as shown in Figures 2 to 5, includes one general-purpose calibration test block and one depth comparison test block. The general-purpose calibration test block consists of 15 test pieces of varying thicknesses, ranging from 1 to 15 mm with a thickness interval of 1 mm. As shown in Figure 2, each test piece has three circular grooves 1 and three regular cross-shaped grooves 2. The depths of the three circular grooves 1 are 7 μm, 15 μm, and 30 μm, respectively. The two straight lines of the three regular cross-shaped grooves 2 are all 6 mm long and the depths of the grooves are 7 μm, 15 μm, and 30 μm, respectively. The diameters of the three circular grooves 1 may be 10 mm, 25 mm, and 40 mm, respectively. As shown in FIG. 2, the smaller circular groove can be placed within the larger circular groove. The test specimen may be a square specimen with a side length of 60 mm. In terms of the diameter, side length, and circular groove arrangement, the diagonal of the test specimen is slightly larger than the spacing between the yokes, which exactly meets the requirements for use and is the minimum dimension scheme.

[0024] As shown in Figures 3 to 5, the depth comparison test block is a diagonal wedge-shaped test block with a flat top and a sloped bottom, and the test block is 150 mm long, 15 mm thick, and ≥ 100 mm wide. A 150 mm scale is engraved on the edge of the flat top of the test block, and three linear grooves 3 with depths of 7 μm, 15 μm, and 30 μm are uniformly formed on the sloped bottom, and marks indicating the groove depths are provided on the side of the test block.

[0025] The material of the calibration comparison test block is the same as the material of the steel lining being inspected, or 45# steel, and its main chemical composition conforms to GB699 "Steel Grades and General Technical Requirements for High-Quality Carbon Structural Steels." After annealing, the grain size should be at least grade 7, and there should be no groove defects or magnetic particle pattern defects larger than 1μm in any direction on the inside or surface. The surface roughness of the test block should be Ra≦0.4μm on each surface, and the edge parallelism≦5μm. There should be no obvious scratches, dents, rust, or other defects on the outer surface.

[0026] Specifically, the inspection steps are as follows:

[0027] Step 1.1: Calibrate and adjust the testing capability of the low-frequency magnetic testing device using the general-purpose calibration test block in the calibration comparison test block.

[0028] Select a calibration test piece whose thickness is equal to or slightly larger than the thin-walled steel lining being measured (e.g., if the steel lining is 4.5 mm thick, select a 5 mm thick test piece). Apply a defect indicator film to the ungrooved side of the test piece. Adjust the pulse frequency of the yoke-type low-frequency magnetic flaw detector to 50 Hz. Place the yoke on the ungrooved side. Start the detector and adjust the pulse frequency until a magnetic particle pattern appears on the indicator film on the calibration test piece. This indicates that the steel lining weld can be inspected using low-frequency magnetic testing alone. Once Step 1 is completed, the entire inspection process is complete. If a magnetic particle pattern does not appear, use other calibration test pieces thinner than the steel lining being measured in order of decreasing thickness until a magnetic particle pattern appears. Record the maximum thickness D of the test piece at which a magnetic particle pattern appears. After Step 1 is completed, the maximum inspection depth for the low-frequency magnetic testing is determined. Steps 2 through 4 are then performed. The parameters of the device when the magnetic particle pattern is displayed are locked as inspection parameters.

[0029] Step 1.2: Conduct an on-site inspection A defect indicator film is attached to the inner surface of the steel lining in the area to be inspected, and a yoke is placed across both sides of the weld. The inspection is carried out in sequence using a crisscross method, with the coverage area of ​​the two inspections overlapping by at least 10% during the movement to ensure no area is missed. An electric current is passed through to magnetize the film, and any changes on the indicator film are continuously observed.

[0030] Step 1.3: Defect Recording After the magnetic particle pattern appears on the defect indicator film, change the magnetic field application angle by at least two different angles, select the angle at which the defect is more prominent, take and save photos on site, mark the location of the magnetic particle pattern, and when the inspection work is completed, cut off the area indicator film and save it.

[0031] Step 1.4: Quantify defect depth using the depth comparison test block in the calibration comparison test block described above.

[0032] After determining the location of the defect magnetic powder pattern, gradually increase the pulse frequency of the low-frequency magnetic flaw detector until the defect magnetic powder pattern just disappears, and then lock the instrument parameters. A defect indicator film is attached to the non-grooved side of the depth comparison test block, the yoke is placed on the non-grooved side, and the inspection device is restarted. The indicated length of the magnetic powder pattern on the surface is observed, and the corresponding defect depth is read by comparing it with the scale (for a ratio of 10:1, if the defect length is 50 mm, the corresponding depth is 5 mm). In this way, the depth of the inspected defect is determined.

[0033] Step 1.5: Inspection grading and quality assessment In accordance with the requirements of the steel lining inspection standard (see NB / T47013.4-2015), the inspection results for the weld seam are graded. If the length of the linear magnetic powder pattern is ≦1.5mm, it is rated as Grade I. If the diameter of the magnetic powder pattern of the circular defect is ≦2.0mm and the number within the evaluation box (the dimensions of the evaluation box are 35mm x 100mm) is 1 or less, it is rated as Grade I. If it exceeds Grade I, it is rated as Grade II. Whether the weld passes or fails is determined in accordance with the provisions of the steel lining quality standard and contract, etc.

[0034] [Embodiment 2] Based on embodiment 1, the following steps are carried out.

[0035] In step 1.1, if a magnetic powder pattern can be displayed on the test piece equal to the thickness of the steel lining, then when the entire inspection work is completed and a magnetic powder pattern has not been displayed on the test piece equal to the thickness of the steel lining throughout, determine the maximum inspection depth D of the low-frequency magnetic inspection and proceed to step 2.

[0036] Step 2: Prep the weld and adjacent base metal surfaces The steel lining is mechanically polished using equipment such as an angle grinder until a metallic luster appears, and the polishing range is 2KT on the surface of the weld and on both sides of the base material, where K is the K value of the probe in the shear wave ultrasonic inspection in step 4, and T is the thickness of the steel lining. The polishing width on one side is at least 50mm.

[0037] Step 3: Recheck the thickness of the steel lining Using equipment such as an ultrasonic thickness gauge, measure the thickness of the base material adjacent to the weld and ensure that the thickness is equal to or greater than the theoretical minimum design thickness of the steel lining.

[0038] Step 4: Inspect the steel lining weld using shear wave ultrasonic testing method.

[0039] For steel linings that are somewhat thick and cannot be fully covered by low-frequency magnetic testing, the maximum inspection depth D for low-frequency magnetic testing is already determined in step 1, and the remaining uninspectable areas are inspected using shear wave ultrasonic testing, which can be applied to inspecting thick steel lining welds, thereby achieving full-coverage inspection of the welds.

[0040] In terms of principle, ultrasonic flaw detection is a non-destructive testing method that uses the energy changes in the reflection of ultrasonic wave propagation waveforms caused by differences in the acoustic properties of materials and their defects to detect internal flaws in materials. The pulse reflection method uses shear waves during angle beam flaw detection, and on the waveform display screen of the ultrasonic device, the abscissa represents the propagation time of the sound wave and the ordinate represents the amplitude of the echo signal. In the same homogeneous medium, the propagation time of the pulse wave is proportional to the sound path length, so the presence of a flaw can be determined by the appearance of a flaw echo signal. The position where the echo signal appears can also be used to determine the distance from the flaw to the detection surface, thereby realizing flaw location, and the echo amplitude can be used to determine the equivalent size of the flaw.

[0041] Equipment process parameters: (1) Inspection method: Pulse reflection ultrasound inspection (A-mode ultrasound). (2) Probe parameters: K2-K5, frequency range: 3≦f≦5MHz. (4) Binding method: water. (5) Type of test block: CSK-IA, a homemade ultrasonic inspection comparison test block. (6) Scanning method: Zigzag scan.

[0042] As shown in Figures 6 and 7, the structure of the homemade ultrasonic inspection comparison test block is a block-like structure with a length of ≥ 310 mm, a thickness of ≥ 40 mm, and a height of 20 mm. Both ends of the length are stepped. The entire block is composed of three sections: a horizontal through-hole region 4 in the middle, a first stepped groove region 5 at each end, and a second stepped groove region 6. The first stepped groove region 5 includes six layers of steps 7, with the step heights of each layer varying by 3 mm, with the step at the end being 3 mm. The width of the groove platform (i.e., the steps) in each layer is ≥ 15 mm. A groove 8 with a width of 0.1 mm and a depth of 1 mm was machined in the center of each groove platform across the width of the ultrasonic inspection comparison test block to simulate a vertical crack at the base of the weld. When using the ultrasonic inspection comparative test block, the probe is obliquely incident on the groove from the underside of the ultrasonic inspection comparative test block to form an echo, and if the root of the groove (i.e., the surface of the groove platform) is taken as the groove depth value, the simulated depths (from the end to the middle) in the groove area on that side are 3 mm, 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, respectively.

[0043] The second stepped groove region 6 includes seven layers of steps 7, each with a step height that varies by 3 mm, with the outermost step being 2 mm. The groove platform (i.e., the step) width for each layer is ≥ 15 mm. A groove 8 with a width of 0.1 mm and a depth of 1 mm is machined in the center of the groove platform across the width of the ultrasonic testing block. When the ultrasonic testing block is in use, the probe is obliquely incident on the groove from the top surface of the ultrasonic testing block to form an echo. The groove depth is taken to be the groove base (i.e., the surface of the groove platform). The simulated depths (from the edge to the middle) in the groove region on that side are 2 mm, 5 mm, 8 mm, 11 mm, 14 mm, 17 mm, and 20 mm, respectively (located on the underside of the ultrasonic testing block).

[0044] The stepped slopes formed in sequence by six layers of steps 7 included in the first stepped trench area 5 and the stepped slopes formed in sequence by seven layers of steps 8 included in the second stepped trench area 6 are arranged in parallel and positioned opposite each other, and can function as a base for joining multiple ultrasonic inspection comparison test blocks for steel lining welds in underground cavities at compressed air energy storage power plants.The side view of the ultrasonic inspection comparison test block for steel lining welds in underground cavities at compressed air energy storage power plants is approximately parallelogram-shaped.

[0045] In the horizontal through-hole region 4 located in the middle, six Φ1 horizontal through-holes 9 are distributed in order from top to bottom, with a horizontal spacing of ≧15 mm between each hole, a distance between the top hole and the edge of the first stepped groove region 5 of ≧25 mm, a vertical spacing of 3 mm, and a distance between the top hole and the top surface of the test block of 3 mm. Therefore, the depths of the horizontal through-holes from top to bottom are 3 mm, 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, and correspondingly, the depths of the horizontal through-holes from bottom to top are 2 mm, 5 mm, 8 mm, 11 mm, 14 mm, and 17 mm, respectively.

[0046] The ultrasonic testing comparative test block has a total height of 20mm, covering the thickness range of the steel linings currently used in underground compressed air energy storage caverns. The test block thickness is ≥ 40mm, meeting the dimensional requirements for the horizontal through-holes required for ultrasonic testing test blocks and better avoiding the effects of sidewall echoes. The material of the ultrasonic testing comparative test block is either the same as the steel lining material being tested or 45# steel, with the main chemical composition conforming to GB699 "Steel Grades and General Technical Requirements for High-Quality Carbon Structural Steels." After annealing, the grain size reaches grade 7 or above. Ultrasonic testing is performed from various directions within the material, and the ultrasonic reflection signal intensity from the tested defects does not exceed the ultrasonic reflection signal intensity generated by a single flat-bottom hole with a diameter of 0.5mm (Φ0.5mm) inside the material. The surface roughness of the test block is Ra≦0.4 μm, and the end face parallelism is ≦5 μm. There are no obvious scratches, dents, rust, or other defects on the outer surface. The depth of each stepped groove is marked on the side of the test block.

[0047] The specific inspection steps are as follows:

[0048] Step 4.1: Determine the leading edge of the probe and the K value Using the CSK-IA test block, the highest reflected waves of the Φ50mm and Φ100mm arcs are found simultaneously through the ultrasonic inspection equipment's specific adjustment program in the first step, and the distance to the front edge of the probe is measured, and then input into the equipment; in the second step, the highest wave of the Φ50mm stepped hole with a depth of 30mm is found, and input into the equipment to determine the actual K value of the probe.

[0049] Step 4.2: Draw a distance-amplitude correction curve (DAC curve) using the above ultrasonic test comparison test block.

[0050] Using the ultrasonic inspection device's own adjustment program, select the first channel and create a DAC curve by selecting all horizontal through-holes whose depth is slightly greater than the thickness of the steel lining (for example, if the steel lining is 6 mm thick, select horizontal through-holes with depths of 2 mm, 3 mm, 5 mm, 6 mm, and 8 mm as the horizontal through-holes for curve creation). Complete the creation of the distance amplitude correction curve, which will be the comparison curve. Select the second channel separately and select a groove depth equal to the thickness of the steel lining to be inspected or the two groove depths closest to that depth as references (for example, if the steel lining is 6 mm thick, select a groove depth of 6 mm; if the steel lining is 7 mm thick, select groove depths of 6 mm and 8 mm). Create a reference point or reference line.

[0051] The DAC curve (Distance Amplitude Correction Curve) is an important tool in ultrasonic inspection to compensate for the change in echo amplitude caused by factors such as sound beam divergence at different distances and material attenuation. By establishing the correction relationship between distance and echo amplitude, the echo amplitude of the same size defects at different distances can be accurately evaluated, thereby ensuring the accuracy and reliability of the inspection results.

[0052] Step 4.3: Conduct on-site inspections Add water as a binder to the polished areas on both sides of the weld being inspected, select the DAC curve created in the first channel, input a 4 dB coupling correction, and adjust the reflection amplitude of the 2 mm deep horizontal through hole to 80% or more of the full screen. Place the ultrasonic probe in the area and perform a zigzag scan at a scan speed of 150 mm / s or less. Monitor the waveform changes on the oscilloscope screen in real time during the scan, focusing on one or three reflection echoes in the TD range at the base of the weld. After scanning one side, repeat the scan on the other side to ensure full coverage of the weld.

[0053] Step 4.4: Defect Recording If the reflected echo is detected to exceed the DAC curve, the defect location and other information shall be reconfirmed from multiple angles on at least both sides of the weld. If the defect is located inside the weld seam, the -6 dB method shall be used to measure the length, and the information on the longer side shall be recorded. The depth, length, position, and amplitude of the defect shall be recorded and its position shall be marked on the surface of the seam. If the detected defect is within the root position of the weld, the reference point or reference line of the second channel shall be called up, and the waveform and reflection equivalent shall be compared to determine the nature and size of the defect.

[0054] Step 4.5: Inspection grading and quality assessment The inspection results shall be graded for the welded seams in accordance with the requirements of the Steel Lining Inspection Standard (see NB / T47013.3-2015).

[0055] 1) If the nature of the defect is determined to be a crack, poor fusion, or incomplete penetration, it will be judged as a failure.

[0056] 2) If the reflection equivalent of the defect exceeds the DAC curve, it is an over-standard defect and is judged as a failure.

[0057] If the reflection equivalent of the defect does not exceed the DAC curve, a. if the length of the single defect is greater than or equal to the plate thickness, it will be judged as a failure; b. if the length of the single defect is less than the plate thickness, it will be judged as a recordable defect, and it will be judged as a pass, and the defect information will be recorded and monitoring will be strengthened in the future.

[0058] [Embodiment 3] The full coverage non-destructive testing method for steel lining welds of underground caverns in compressed air energy storage power plants, specifically: Step 1: Use a low-frequency magnetic inspection method to inspect the steel lining weld for defects and determine the defect depth. At the same time, use a general-purpose calibration test block in the calibration comparison test block to determine the inspectable thickness range of the low-frequency magnetic inspection method. If the inspectable thickness range covers the thickness of the steel lining to be inspected, the weld inspection work is completed. If it does not cover the thickness, proceed to step 2. Step 2: Pretreating the surface of the steel lining weld to be inspected and the surface of the adjacent base material to give it a metallic luster; Step 3: Recheck the thickness of the steel lining; Step 4 is to use a shear wave ultrasonic inspection method to inspect the steel lining weld area not inspected by the low frequency magnetic inspection method in step 1. [Explanation of symbols]

[0059] 1. Circular groove, 2. Regular cross groove, 3. Straight groove, 4. Horizontal through-hole area, 5. First stepped groove area, 6. Second stepped groove area, 7. Step, 8. Groove, 9. Horizontal through-hole.

Claims

1. 1. A full coverage non-destructive inspection method for steel lining welds of underground caverns in compressed air energy storage power plants, specifically comprising: Step 1: Using a low-frequency magnetic inspection method to inspect the steel lining weld for defects and determine the defect depth, and at the same time, using a general-purpose calibration test block in the calibration comparison test block to determine the thickness range that can be inspected by the low-frequency magnetic inspection method. If the thickness range that can be inspected covers the thickness of the steel lining to be inspected, the weld inspection work is completed, and if it does not cover the thickness, proceed to step 2. Step 2: Pretreating the surface of the steel lining weld to be inspected and the surface of the adjacent base material to give it a metallic luster; Step 3: Recheck the thickness of the steel lining; A full-coverage non-destructive testing method for steel lining welds in underground cavities of compressed air energy storage power plants, characterized by being carried out in accordance with step 4, in which areas of the steel lining welds not inspected using the low-frequency magnetic testing method in step 1 are inspected using a shear wave ultrasonic testing method.

2. Specifically, step 1 is Step 1.1: determining the thickness range that can be inspected by the low-frequency magnetic inspection method using a universal calibration test block in a calibration comparison test block; Defect inspection is carried out using a low-frequency magnetic flaw detector, specifically: Step 1.2: attaching a defect indicator film to the inner surface of the steel lining to be inspected, placing a yoke across both sides of the weld, inspecting sequentially using a crisscross method, ensuring that the coverage area of ​​the two inspections overlaps by at least 10% during the movement to ensure no inspection is missed, passing electricity through the film to magnetize it, and continuously observing any changes on the indicator film; Step 1.3: after the magnetic particle pattern appears on the defect indication film, change the magnetic field application angle to at least two different angles, select the angle at which the defect indication is more prominent, take and save a photo on-site, and mark the position of the magnetic particle pattern; Step 1.4 quantifying defect depth using depth comparison test blocks in the calibration comparison test blocks; 2. The full-coverage non-destructive inspection method for steel lining welds in underground cavities of compressed air energy storage power plants according to claim 1, characterized in that it is carried out in accordance with step 1.5, which comprises rating the inspection results for the steel lining welds.

3. Regarding the specific structure of the calibration comparison test block, The calibration comparison test block includes a set of general-purpose calibration test blocks and one depth comparison test block, and the general-purpose calibration test block consists of 15 test pieces with a thickness interval of 1 mm, the thinnest test piece being 1 mm thick and the thickest test piece being 15 mm thick. The surface of the test piece is provided with three circular grooves (1) of different depths and three regular cross-shaped grooves (2) of different depths, the depths of the circular grooves (1) being 7 μm, 15 μm, and 30 μm, respectively, and the lengths of the two straight lines of the regular cross-shaped grooves (2) are both 6 mm, and the depths of the grooves are 7 μm, 15 μm, and 30 μm, respectively. The depth comparison test block is an oblique wedge-shaped test block, 150 mm long and 15 mm thick, with a flat top and a sloped bottom, a 150 mm scale engraved on the edge of the flat top, and three linear grooves (3) of different depths are uniformly formed on the sloped bottom, with the groove depths being 7 μm, 15 μm, and 30 μm, respectively.

4. In step 1.1, the specific steps for determining the testable thickness range of the low-frequency magnetic inspection method using the universal calibration test block are as follows: Select one test piece from the universal calibration test block, and the thickness of the test piece is the same as that of the thin-walled steel member to be measured, or the thickness of the test piece is closest to and greater than that of the thin-walled steel member, and then attach a defect indicator film to the non-grooved surface of the test piece; Adjust the pulse frequency of the yoke-type low-frequency magnetic flaw detector to 50 Hz, place the yoke on the non-grooved surface, and start the flaw detector. If the pulse frequency value can be adjusted until a magnetic particle pattern appears on the indicator film on the calibration test piece, it indicates that the thickness range that can be inspected by low-frequency magnetic testing covers the thickness of the steel lining to be inspected; The full-coverage non-destructive testing method for steel lining welds in underground cavities in compressed air energy storage power plants described in claim 3, characterized in that if the magnetic particle pattern does not appear throughout, other calibration test pieces thinner than the thickness of the steel lining to be measured are used to test in order of decreasing thickness until the magnetic particle pattern appears, and the maximum thickness D of the test piece at which the magnetic particle pattern can be displayed is set as the maximum testing depth of the low-frequency magnetic testing.

5. In step 1.4, the specific steps for quantifying the defect depth using the depth comparison test block are as follows: After determining the location of the defect magnetic powder pattern, gradually increase the pulse frequency of the low frequency magnetic flaw detector until the defect magnetic powder pattern just disappears, and lock the instrument parameters at this time; Affix the defect indicator film to the non-grooved surface of the depth comparison test block, place the yoke on the non-grooved surface, restart the inspection device, The full-coverage non-destructive inspection method for steel lining welds in underground cavities at compressed air energy storage power plants according to claim 3, characterized in that the depth of the inspected defect is determined by observing the indicated length of the magnetic particle pattern on the surface, comparing it with a scale, and reading the corresponding defect depth.

6. Specifically, step 4 is Using the CSK-IA test block, the first step is to simultaneously find the highest reflected waves of the Φ50mm and Φ100mm arcs through the ultrasonic inspection device's specific adjustment program, measure the distance to the front edge of the probe, and then input it into the device; In the second step, step 4.1 finds the highest wave of the Φ50mm stepped hole with a depth of 30mm and inputs it into the instrument to determine the actual K value of the probe; Step 4.2: plotting a DAC curve using an ultrasonic test comparison block to create a reference point or line; Step 4.3: Apply water as a binder to the polished areas on both sides of the weld to be inspected; select the DAC curve created by the first channel; perform 4 dB coupling compensation; adjust the reflection amplitude of the 2 mm deep horizontal through-hole to 80% or more of the full screen; place the ultrasonic probe on the polished area and perform a zigzag scan at a scan speed of 150 mm / s or less; monitor the waveform changes on the oscilloscope screen in real time during the scan; focus on observing one or three reflection echoes in the T-D range of the root of the weld; after completing the scan on one side, repeat the scan on the other side to ensure full coverage inspection of the weld; If it is detected that the reflected echo exceeds the DAC curve, the defect position information is reconfirmed from multiple angles at least on both sides of the weld. If the defect is inside the weld seam, the length is measured using the -6 dB method, and the information on the side with the longer length is recorded as the recorded information. The depth, length, position and amplitude of the defect are recorded. Step 4.4: marking the position on the surface of the seam, and if the inspected defect is within the root position of the weld, calling the reference point or reference line of the second channel, comparing the waveform and reflection equivalent, and determining the nature and size of the defect; 4.

5. The full-coverage non-destructive inspection method for steel lining welds in underground cavities of compressed air energy storage power plants according to claim 1, characterized in that it is carried out in accordance with step 4.5, which comprises inspecting, grading, and evaluating the quality of the steel lining welds.

7. In step 4.2, the specific structure of the ultrasonic inspection comparative test block is as follows: The ultrasonic inspection comparative test block is composed of three parts, each of which is a horizontal through-hole region (4) located in the middle, a first stepped groove region (5) located at both ends, and a second stepped groove region (6); In the transverse through-hole region (4), six transverse through-holes (9) are distributed in order from top to bottom, the horizontal interval between each transverse through-hole (9) is ≥ 15 mm, the vertical interval between each transverse through-hole (9) is 3 mm, the distance between the topmost transverse through-hole (9) and the top surface of the ultrasonic inspection comparative test block is 3 mm, and the distance between the bottommost transverse through-hole (9) and the bottom surface of the ultrasonic inspection comparative test block is 2 mm; The first stepped groove region (5) includes six layers of steps (7), the height of the steps (7) of each layer differing by 3 mm, and the height of the step (7) located at the end is 3 mm; The second stepped groove region (6) includes seven layers of steps (7), the height of the steps (7) of each layer differing by 3 mm, and the height of the step (7) located at the outermost end is 2 mm; The full-coverage non-destructive testing method for steel lining welds in underground cavities at compressed air energy storage power plants, as described in claim 6, characterized in that a groove (8) 0.1 mm wide and 1 mm deep is provided in the width direction of the ultrasonic testing comparison test block at the center of the step (7).

8. Step 4.2 specifically includes: A first channel is selected by an adjustment program specific to the ultrasonic inspection device, and according to the thickness of the steel lining, all of the transverse through holes whose depths are greater than the thickness of the steel lining and closest to the thickness of the steel lining are selected to create a DAC curve, and the DAC curve is used as a comparison curve; The full-coverage non-destructive inspection method for steel lining welds in underground cavities at compressed air energy storage power plants according to claim 7, characterized in that a second channel is separately selected, and a groove depth equal to the thickness of the steel lining to be inspected or two groove depths closest to that groove depth are selected as reference points or reference lines.

9. In step 4.4, the specific grading criteria are: 1) If the defect is characterized as a crack, poor fusion, or incomplete penetration, it will be judged as a failure. 2) If the reflection equivalent of the defect exceeds the DAC curve, it is an over-criteria defect and is judged as a failure; and If the reflection equivalent of the defect does not exceed the DAC curve, a. If the length of a single defect is greater than or equal to the plate thickness, it is judged as unacceptable. The full-coverage non-destructive inspection method for steel lining welds in underground caverns of compressed air energy storage power plants according to claim 6, wherein if the length of a single defect is less than the plate thickness, it is determined to be a recordable defect and is determined to be pass.

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