Directional detection method for hidden cracks in main beam of metallurgical crane

Abstract

The invention relates to a directional detection method for hidden cracks in a metallurgical crane girder, and belongs to the technical field of detection. The problems of low crack detection efficiency and high omission ratio of the weld joint area in the metallurgical crane box type girder are solved. The method comprises the following steps: firstly, determining an internal key hidden welding seam area based on multi-axis high-cycle fatigue simulation, planning a preset guided wave path pointing to the area from the outer surface of a main beam for each area, and establishing a path mapping relation; secondly, setting a permanent physical reference mark on an external corresponding detection point; and finally, during detection, the probe is accurately positioned and coupled through a mark, mapping parameters are called to excite guided waves to propagate along a preset path, and by comparing an echo signal with a reference signal pre-stored at the point, whether a crack exists at the tail end of the path or not is judged, and the size of the crack is evaluated. According to the invention, accurate directional detection is realized, the detection repeatability is ensured through a physical reference, efficient, accurate and standardized detection of internal specific hidden cracks is realized, and entering the box body is not needed.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing and condition monitoring technology, and in particular to a method for directional detection of hidden cracks inside the main beam of a metallurgical crane. Background Technology

[0002] Box-type main beams are widely used in heavy equipment such as metallurgical cranes due to their excellent load-bearing capacity. Their complex internal diaphragm and stiffening rib structures are welded to the cover plate and web, forming numerous load-bearing welds. These internal weld areas are highly susceptible to fatigue crack initiation under long-term high-cycle, multi-axis alternating loads. Due to their extremely concealed location and confined space, these cracks become a blind spot for traditional non-destructive testing techniques and a significant safety hazard.

[0003] Currently, the detection of such internal hidden cracks mainly relies on two methods: First, periodically stopping the machine and opening the inspection port, allowing inspection personnel to enter the enclosure for close-range sampling. This method is inefficient, costly, involves a harsh working environment, and poses safety risks, failing to achieve comprehensive and rapid screening. Second, conducting large-area conventional ultrasonic scanning on the outside of the main beam. This method lacks a precise spatial correspondence between internal defect locations and external measuring points, and the propagation path of sound waves in complex structures is uncertain and subject to numerous interferences. This results in poor detection specificity, low signal-to-noise ratio, and an unsatisfactory detection rate for micro-cracks. It also heavily relies on the operator's experience, leading to insufficient repeatability and reliability of the results. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for directional detection of hidden cracks inside the main beam of a metallurgical crane. By establishing a precise acoustic path mapping relationship between high-risk internal parts and external detection points, ultrasonic guided waves are used for directional excitation and reception along a preset path to achieve rapid, accurate and repeatable detection of specific hidden cracks inside the crane without entering the interior of the crane.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for directional detection of hidden cracks inside the main beam of a metallurgical crane, comprising the following sequential steps: S1. Path Mapping Construction: For the box girder to be inspected, the key hidden weld areas that require focused monitoring are first identified. Then, for each key area, an optimal ultrasonic guided wave propagation path is planned, pointing from a selected inspection point on the outer surface of the main girder towards that specific area, serving as the preset guided wave path. Finally, a unique mapping relationship is established and stored between the coordinates of the external inspection points and the corresponding preset guided wave path parameters (including direction, length, and target area description).

[0006] Preferably, the determination of the critical concealed weld area is based on multi-axis high-cycle fatigue simulation analysis of the main beam structure, identifying the internal weld end area where the cumulative fatigue damage value exceeds a preset safety threshold.

[0007] Preferably, the planning principle of the preset waveguide path is that its designed wave propagation direction, when reaching the critical concealed weld area, should maintain an approximately perpendicular relationship with the fatigue crack initiation surface most likely to occur in that area, as determined through simulation or historical experience. This maximizes the waveguide's sensitivity to crack reflection.

[0008] S2. Reference Setting: At each external detection point location determined in step S1, a permanent physical reference mark is machined or installed on the outer surface of the main beam. This mark is used to accurately locate and couple the ultrasonic guided wave probe in all subsequent inspections.

[0009] Preferably, the permanent physical reference mark is a alignment structure such as a groove, boss, or inlay block formed by machining. During testing, the ultrasonic guided wave probe is installed using a dedicated positioning fixture that matches the shape of this structure, thereby ensuring a high degree of repeatability of the probe's position, angle, and coupling state for each test.

[0010] S3. Oriented Detection: In actual testing, the ultrasonic guided wave probe is first precisely coupled to a physical reference mark using the positioning fixture. Then, based on the mapping relationship established in step S1, the optimal detection parameters preset for that point are invoked. Next, an ultrasonic guided wave is generated, which propagates strictly along a preset guided wave path into the main beam. Finally, the reflected signal or the signal after penetration returned from this path is received and analyzed to determine whether a crack exists in the target area at the end of the path.

[0011] Preferably, the selection of the detection parameters is based on the length of the preset waveguide path and the thickness of the main beam plate, specifically including selecting a waveguide mode sensitive to the opening and closing of the crack surface (such as SH wave or symmetrical Lamb wave) and a matching center frequency.

[0012] More preferably, the signal analysis employs a benchmark comparison method: when the main beam is in a known defect-free state (e.g., newly manufactured or after major repair), a test is performed at each detection point, and the obtained signal is stored as the benchmark signal for that point. In subsequent service life inspections, the real-time acquired signal is compared with this benchmark signal in the time domain (e.g., amplitude, time of arrival) or the frequency domain (e.g., spectrum, energy). If a significant difference is found (e.g., the appearance of a new reflected wave or abnormal signal energy attenuation), it is determined that a crack has appeared in the region at the end of the preset path.

[0013] Furthermore, after determining the presence of a crack, the distance between the crack and the external detection point can be calculated by analyzing the arrival time of the abnormal reflection signal, thus achieving precise location; by analyzing the relative amplitude or energy of the abnormal reflection signal, the equivalent size of the crack can be preliminarily assessed.

[0014] The present invention also provides a detection system for implementing the above method, characterized in that it comprises: Database module: Used to store the path mapping relationship of all detection points, the optimal detection parameters, and historical reference signals.

[0015] Probe positioning coupling device: used in conjunction with the physical reference marks on the main beam to achieve rapid and accurate positioning of the probe.

[0016] Ultrasonic guided wave excitation and receiving device: It can generate excitation signals and collect echo signals by calling parameters from the database.

[0017] Signal analysis module: Built-in benchmark comparison algorithm, which can automatically analyze signal differences and output diagnostic conclusions.

[0018] The beneficial effect of this invention is that it solves the defects existing in the prior art. 1. The detection objective is clear and the path is optimal, which greatly improves the detection efficiency and crack detection rate.

[0019] 2. By using physical reference marks and dedicated fixtures, positioning errors caused by human operation are eliminated, the detection process is standardized, and the results have high repeatability and comparability, which facilitates long-term status tracking.

[0020] 3. It adopts a reference signal comparison mode, which is extremely sensitive to minute changes in the signal and can identify early micro-cracks or damage initiation that are difficult to detect by traditional methods, thus achieving true early warning.

[0021] 4. Testing personnel do not need complex judgments; they only need to find the benchmark point according to the diagram and install the equipment to complete professional-level testing, reducing reliance on personnel experience. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a block diagram illustrating the system structure principle of the present invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and preferred embodiments. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0024] like Figures 1-2As shown, this embodiment describes the directional detection of hidden cracks inside the main beam of a metallurgical crane. It focuses on a 260 / 80-ton casting crane operating in a steelmaking workshop. The main beam has an A8 working class and is subjected to long-term radiant heat from molten steel ladles (approximately 1600°C), frequent starting and braking impacts, and heavy-load skewed operations. Its internal structure is constantly under high temperature and complex multiaxial alternating stress. The main beam is a wide-flange off-center box-type structure with dense longitudinal stiffening ribs and multiple transverse diaphragms inside.

[0025] Implementation steps: Step 1: Path Mapping Construction (Specialized Analysis Based on Metallurgical Working Conditions) This step is completed during the crane design phase or the safety assessment phase before the first major overhaul, and is part of the core technology preparation phase.

[0026] 1. Load spectrum and thermal field analysis: The load spectrum of the crane's typical working cycle was collected, including full ladle lifting, loaded operation, emergency braking, and empty hook return. At the same time, combined with infrared thermography data, a non-uniform steady-state temperature field model of the lower cover plate and one side web plate of the main beam was established (the radiation from the molten steel ladle caused the local area of ​​the lower cover plate to be at 80-120°C for a long time).

[0027] 2. Multiaxial High-Cycle Fatigue Simulation: Establish a refined finite element model containing all internal weld details. Simultaneously apply the mechanical load spectrum and temperature field from step 1 to perform multiaxial high-cycle fatigue simulation under thermo-mechanical coupling. The simulation software (such as Fe-safe) employs a multiaxial fatigue algorithm based on the critical plane method (such as the Wang-Brown criterion) to calculate the fatigue damage contour map of each weld region.

[0028] 3. Identifying Key Hidden Areas: Simulation results clearly identify the hotspots where fatigue damage is most concentrated. In this embodiment, the first key area identified is located on the downstream side of the main beam mid-span, at the termination end of the fillet weld between the longitudinal T-stiffener and the lower cover plate. This area bears the superposition of the maximum bending normal stress and welding residual stress, and the material fatigue strength decreases due to high temperature, resulting in damage values ​​far exceeding those of other locations. The second key area is located at the end of the weld connecting the diaphragm and web plate near the end beam, subjected to a combination of local shear and bending forces caused by wheel pressure.

[0029] 4. Plan the preset waveguide path: For the first critical area (where cracks are most likely to initiate from the weld toe along the plate thickness or along the weld longitudinal direction), a "vertical path" is planned. That is, starting from the outer surface of the lower cover plate directly below the weld toe (location P1), the detection point is set, and the path direction is vertically upward, passing through the 28mm thick lower cover plate to the weld toe. This path direction is intended to be perpendicular to the most dangerous crack surface that extends along the plate thickness.

[0030] For the second critical area (where the crack is most likely to propagate from the weld toe into the web), a "horizontal path" is planned. That is, starting from the outer surface of the outer web (position P2) as the detection point, the path direction is horizontal inward, passing through the 22mm thick web and reaching the weld toe.

[0031] 5. Establish a mapping database: Create digital profiles for points P1 and P2. Record their global coordinates, corresponding internal target areas (e.g., "end of the weld of the third stiffening rib across the middle and lower reaches"), preset path vectors, and optimal detection parameters calculated based on path length, plate thickness, and the acoustic characteristics of the material at the estimated temperature. For example, for point P1: use a 2.0MHz SH0 type horizontal shear wave (because it is sensitive to vertical cracks due to its propagation in the thickness direction and is less affected by temperature gradients); for point P2: use a 1.5MHz A0 type Lamb wave (sensitive to near-surface defects).

[0032] Step 2: Set physical reference markers (permanent markers adapted to the metallurgical environment). This step is performed during the crane's overhaul at the factory.

[0033] 1. Based on the coordinates in the database, accurately lay out and locate points P1 and P2 on site.

[0034] 2. Marking process: Considering the dusty and oily environment of the metallurgical workshop, a permanent marking process combining deep carving and inlay is adopted.

[0035] At point P1 (lower cover plate), a weathering steel cross groove with a depth of about 0.5 mm is etched using a laser marking machine, and a miniature hard alloy dot is inlaid at the center of the groove as a tactile reference.

[0036] At point P2 (web), weld a base made of heat-resistant stainless steel with locating pin holes. The surface of the base is higher than the paint surface to prevent it from being covered.

[0037] 3. Fabrication of Matching Fixtures: Machining matching probe positioning fixtures. The P1 point fixture has a boss at the bottom that engages with the cross-shaped groove and a probe for locating alloy points; the P2 point fixture is connected to the base hole via a positioning pin. All fixture materials possess a certain degree of heat resistance.

[0038] Step 3: Targeted Inspection Operation (adapted to the inspection process in metallurgical workshops) This step is used for routine inspections or periodic safety checks.

[0039] 1. Acquiring the Reference Signal (Health Record Establishment): The initial test is conducted after the overhaul is completed and the crane is accepted under no-load conditions. The testing personnel use a specialized fixture to quickly install the electromagnetic ultrasonic (EMAT) probe onto the reference point P1. The instrument (such as a portable guided wave instrument with a associated database) automatically identifies the test point number and calls the preset parameters (SH0, 2.0MHz). The acquired signal is displayed as a clean bottom surface echo, which is saved as "P1_Reference Signal" and stored in both the instrument and cloud database. Point P2 is processed in the same way.

[0040] 2. Periodic inspections and intelligent diagnostics during service life: Scenario: The crane is inspected every 3 months by taking 2 hours of planned downtime.

[0041] Operation: The testing personnel arrive at the site with the instrument and fixtures. Clean the reference point P1, install the probe, and the instrument automatically completes coupling checks, parameter loading, signal excitation, and acquisition.

[0042] Analysis: The instrument's built-in algorithm compares the real-time signal with the "P1_reference signal" in the time domain for coherence and analyzes the reflected wave energy. This test revealed a weak but persistent reflected wave F1 in the signal at point P1, preceding the bottom echo.

[0043] Diagnostic output: The instrument screen displays: "Detection point P1: Alarm. Abnormal reflection signal detected, confidence level 92%. Crack location: Approximately 26mm from the detection surface (corresponding to the weld toe position). Equivalent size assessment: Microcrack (length < 5mm). Recommendation: Shorten the monitoring cycle to 1 month." Reporting and Decision-Making: Inspection reports are automatically uploaded to the equipment management platform. Based on this, equipment engineers designate the main beam area as a key monitoring target, avoiding unplanned downtime for inspection, and scientifically scheduling the next major overhaul based on the crack propagation trend.

[0044] Technical effectiveness verification: To verify the effectiveness of this method under simulated metallurgical conditions, a sample taken from the main beam of a scrapped metallurgical crane was processed in the laboratory. Artificial fatigue cracks were pre-introduced in the critical weld areas of the sample. The method of this invention (detection via pre-introduced reference points) and conventional ultrasonic climbing wave method by two experienced inspectors were used for external scanning. The results show: The method of this invention: by detecting two reference points, the total time is 5 minutes, and the location and relative size of the crack are accurately reported, and the results are consistent with the actual internal situation.

[0045] Conventional scanning method: Two people spent an average of 40 minutes scanning the relevant area. One person missed a tiny crack, while the other person detected it but the location was unclear, and there was a significant disagreement on the size of the crack.

[0046] The above description is only a specific embodiment of the present invention. Various examples and illustrations do not constitute a limitation on the substantive content of the present invention. Those skilled in the art can make modifications or variations to the above-described specific embodiments after reading the specification without departing from the substance and scope of the invention.

Claims

1. A method for directional detection of hidden cracks inside the main beam of a metallurgical crane, characterized in that: Includes the following steps, S1. Path mapping construction: For the target box girder, determine the key hidden weld areas to be monitored inside; plan a preset waveguide path for each key area from the detection point on the outer surface of the main girder to its specific direction; Establish and store the mapping relationship between the external detection points and the preset waveguide path; S2. Reference setting: Permanent physical reference marks are set at the detection point positions on the outer surface of the main beam for precise positioning and coupling of the ultrasonic guided wave probe; S3. Directional detection: The ultrasonic guided wave probe is positioned and coupled according to the physical reference mark; the corresponding detection parameters are called according to the mapping relationship to excite and generate ultrasonic guided waves that propagate inward along the preset guided wave path; The system receives and analyzes reflected or transmitted signals from the path, and determines whether there are cracks in the area at the end of the path based on the signal characteristics.

2. The method for directional detection of hidden cracks inside the main beam of a metallurgical crane as described in claim 1, characterized in that: In step S1, the method for determining the key hidden weld area includes: based on the multi-axis high-cycle fatigue simulation analysis of the main beam, identifying the internal weld end area where the fatigue damage value exceeds a preset threshold.

3. The method for directional detection of hidden cracks inside the main beam of a metallurgical crane as described in claim 1, characterized in that: In step S1, the preset waveguide path is planned such that its propagation direction is approximately perpendicular to the crack surface most likely to initiate in the critical concealed weld area, as determined by simulation or experience.

4. The method for directional detection of hidden cracks inside the main beam of a metallurgical crane as described in claim 1, characterized in that: In step S2, the permanent physical reference mark includes a machining-formed alignment groove or protrusion structure, and the ultrasonic waveguide probe achieves repeatable and precise positioning and angle alignment through a positioning fixture that matches the structure.

5. The method for directional detection of hidden cracks inside the main beam of a metallurgical crane as described in claim 1, characterized in that: In step S3, the detection parameters include the waveguide mode and center frequency selected based on the length of the preset waveguide path and the thickness of the main beam plate; wherein, the waveguide mode is an SH wave or a symmetrical Lamb wave that is sensitive to the opening and closing of the crack surface.

6. A method for directional detection of hidden cracks inside the main beam of a metallurgical crane as described in claim 1 or 5, characterized in that: In step S3, when the main beam in a defect-free state is inspected for the first time, the signal of the current inspection point is stored as a reference signal; in subsequent inspections, the abnormal reflection or signal attenuation caused by cracks is identified by comparing the real-time signal with the reference signal in the time domain or frequency domain.

7. The method for directional detection of hidden cracks inside the main beam of a metallurgical crane as described in claim 6, characterized in that: The distance from the crack location to the external detection point is calculated by analyzing the arrival time of the abnormal reflection signal; the equivalent size of the crack is evaluated by analyzing the amplitude or energy of the abnormal reflection signal.

8. The method for directional detection of hidden cracks inside the main beam of a metallurgical crane as described in claim 1, characterized in that: The detection system used in this method includes, The path mapping database module is used to store the mapping relationship between detection points and preset waveguide paths, as well as excitation parameters; A reference positioning and probe coupling device is used to precisely position and couple the probe to a physical reference mark; A guided wave excitation receiver is used to automatically load parameters and excite the received signal according to the selected detection point. The signal analysis and diagnosis module is used to automatically compare and analyze signals and output diagnostic results.

Images