Analysis of the Causes of Broken Lifting Lugs in Large Equipment and Preventive Measures

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Analysis of the Causes of Breakage in Lifting Lugs of Large Equipment and Preventive Measures: In lifting operations in industrial production and construction, lifting lugs serve as the key components that connect the equipment to the lifting tools; their safety and reliability are directly related to the success or failure of the entire operation. Once the lifting lugs break or fall off, it not only leads to damage to the equipment but can also result in serious injuries or fatalities. Therefore, conducting a thorough analysis of the causes of lugs breaking and taking effective preventive measures is key to ensuring the safety of lifting operations. I. Analysis of the main reasons for hook ear fracture 1. Unreasonable design: Stress concentration and structural defects. The design of hook ears must take into account factors such as the equipment’s weight, shape, direction of forces applied, and dynamic loads. If there are defects during the design phase, such as insufficient lug size, inadequate thickness, too small a radius of curvature, or an unreasonable structural shape, it is very likely to lead to stress concentration. For example, if an arc-shaped transition design is not used at the edges of holes or at corners of lifting lugs, local stress will increase sharply during lifting, and cracks will form and propagate as a result of repeated stress over time. Furthermore, if the dynamic loads during lifting (such as vibration and impact) are not properly assessed, it may also lead to the breakage of the lifting lugs under sudden stresses. 2. Material issues: Substandard performance and potential defects. The choice of material for the lifting lugs is crucial. If steel with insufficient strength or toughness is used (such as low-carbon steel in place of high-strength alloys), it is highly prone to plastic deformation or brittle fracture under heavy load conditions. Furthermore, internal defects in the material (such as inclusions, pores, cracks) or improper surface treatment (such as an overly thick decarburized layer) can also significantly reduce its load-bearing capacity. For example, in one project case, the use of steel with an excessive sulfur content in the lifting lugs led to the embrittlement of the heat-affected zone of the welds, resulting in sudden fracture during lifting and causing a serious accident. 3. Installation and welding defects: Irregular processes lead to potential hazards. Misaligned installation positions and substandard welding quality are common causes of lugs failing. If the lifting lugs are not properly aligned with the direction of force during installation, or if the bolts are not tightened to the required torque, it will lead to abnormal concentration of local stress. In terms of welding, incomplete penetration of the weld seam, cracks, pores, or the absence of post-weld heat treatment can all reduce the structural strength. For example, during the lifting of a boiler’s water wall in a certain project, the strength was not recalculated due to a change in the design of the double-hole lugs, and the welding procedures were not carried out in accordance with the relevant standards; as a result, the base of the lugs tore, almost leading to an accident in which the equipment could have fallen. 4. Improper use and maintenance: Fatigue damage and corrosion accumulation. Prolonged repeated use or exposure to harsh environments (such as high temperatures and corrosive substances) can accelerate fatigue damage to the lifting lugs as well as the degradation of their material. If the wear condition of the lifting lugs is not checked regularly, and potential issues such as cracks and deformation are not detected in a timely manner, the risk of fracture increases significantly. For example, the lifting lugs of a chemical plant suffered severe surface corrosion due to prolonged exposure to an acidic environment; despite multiple repair welds, the underlying risks could not be completely eliminated, and eventually they broke suddenly during lifting. II. Key measures to prevent hook breakage 1. Strengthen design review and mechanical verification: The design of hooks must be carried out by qualified professional engineers, who use methods such as finite element analysis (FEA) to simulate the complex stress patterns during lifting processes, thereby ensuring the structural strength and safety. Special attention should be paid to stress concentration areas, and local stress should be reduced by optimizing the radius of fillets and adding reinforcement ribs. At the same time, it is necessary to strictly adhere to relevant standards (such as ASME, GB/T 28263), and adjust the safety factor according to actual operating conditions. 2. Strict control over material quality and welding processes: High-strength low-alloy steels that meet standards (such as Q345B and 35CrMo) are used, and rigorous inspection upon arrival at the factory is carried out to ensure that their chemical composition and mechanical properties meet the required standards. Qualified welders must be employed during welding, and the Welding Procedure Specification (WPS) must be strictly followed. Preheating temperature, interpass temperature, and post-weld heat treatment should be controlled to prevent hydrogen-induced cracks and residual stresses. After the welding is completed, non-destructive testing (such as magnetic particle or ultrasonic testing) must be carried out to ensure there are no defects. 3. Standardized installation and process supervision: Before installation, it is necessary to verify the model, position, and direction of the lifting lugs, and use specialized tools to tighten them to ensure even distribution of forces. During lifting operations, a dedicated supervisor should be assigned to monitor the condition of the lifting lugs and connection points in real time, and operations must be stopped immediately if any abnormalities are detected. For major lifting projects, it is recommended to use a wireless stress monitoring system to provide real-time alerts for dangerous stress levels. 4. Establish a regular inspection and maintenance system. Develop a regular inspection plan for the lifting lugs, focusing on checking the welds, stress-bearing areas, and surface condition. Methods such as visual inspection, ultrasonic thickness measurement, and magnetic particle testing are used to assess the degree of damage; material hardness testing or metallographic analysis may be conducted if necessary. Any issues identified must be repaired promptly; it is strictly prohibited to use the device while it is damaged. In addition, a record-keeping system for lifting lugs should be established to document the parameters of each lift and the inspection data, providing a basis for life assessment. 5. Promote the design and use of standardized lifting lugs; give priority to proven standardized lug structures (such as pin-type and plate-type lugs) to reduce the use of custom-made, non-standard lugs. For example, the main lifting lugs of vertical equipment adopt a tube-shaft structure, with stress being dispersed by increasing the shaft diameter and support area ； The tail hook adopts a plate-type structure, facilitating adjustment to forces from multiple directions. Standardized design not only improves safety but also reduces manufacturing and testing costs. III. Case Warnings and Directions for Technical Improvement: A fracture accident occurred at a construction site due to the incorrect use of the material for the lifting lugs; the design called for Q345B material, but actually lower-strength A3 steel was used, with folding defects on its surface. While lifting an 8-ton concrete column, the lifting lugs suddenly broke, resulting in 6 casualties. This case exposes issues such as chaotic material management and lack of testing. To this end, companies need to establish a strict material tracking system that keeps records throughout the entire process, from procurement and storage to use, in order to prevent the substitution of inferior materials with higher-quality ones. In the future, with the advancement of intelligent monitoring technologies, it is possible to explore embedding sensors in key areas of the lifting lugs to monitor data on stress, temperature, and fatigue damage in real time, enabling remote early warnings through an Internet of Things platform. Furthermore, the use of new high-strength composite materials (such as carbon fiber-reinforced metal matrix composites) is expected to further enhance the load-bearing capacity and fatigue resistance of the lugs. IV. Conclusion: Ensuring the safety of lifting operations for large-scale equipment requires oversight throughout its entire life cycle, from design and manufacturing to installation and use. Preventing lugs from breaking relies not only on the upgrading of technical solutions but also requires companies to adopt a \"zero-accident\" safety philosophy, strictly adhere to standards and regulations, and enhance employee training as well as their sense of responsibility. Only in this way can a solid safety barrier be established to prevent such tragedies from happening again.