Measures to Prevent Loosening and Breakage of Crane Bolts

Feb 26, 2026

Most bolt failures result from loosening. Once loosening occurs, significant kinetic energy is transferred directly between the bolt and the clamped component. Under axial loading, this can cause the bolt to fracture due to tensile forces. Under radial loading, the bolt hole may deform into an oval shape, leading to shearing of the bolt.

To effectively prevent the loosening and breakage of pipe clamp fixing bolts, the following measures should be implemented:

Regular Inspection for Plastic Deformation

Bolts under sustained load are prone to internal plastic deformation. As plastic strain increases, elastic deformation diminishes, resulting in a loss of clamping force. This type of thread loosening develops gradually and is difficult to detect early. Therefore, the fixing bolts of rigid pipes should be inspected approximately every 200 operating hours for signs of abnormality.

Optimize Bolt Specifications for Anti-Loosening

A direct and effective method to enhance anti-loosening performance is to increase the bolt diameter and utilize fine threads. A larger diameter allows for higher preload and improved friction, while fine threads provide a smaller helix angle, increasing frictional resistance against loosening. Flat washers offer superior rigidity compared to bolts; however, any decline in bolt performance reduces the axial tensile force transmitted to the washer, increasing the risk of loosening. Upgrading bolt specifications helps mitigate this.

Use Thickened Flat Washers to Prevent Bending

Spring washers can introduce uneven elasticity, causing bolt bending. Bent bolts are particularly susceptible to loosening and failure under vibration and impact. To avoid inducing bending stress, a combination of spring and flat washers should be avoided. Instead, a single thickened flat washer is recommended. This washer should be manufactured from 45# steel, subjected to medium-temperature quenching and tempering to achieve a hardness of approximately HRC 38–42. During electroplating processes such as galvanizing, precautions must be taken to prevent hydrogen embrittlement. The washer surface must be smooth, free from cracks, burrs, or other defects.

Apply Thread-Locking Adhesive and Torque Marking

Before assembly, apply a thread-locking adhesive to the engaged threads to effectively prevent loosening. Tighten all fixing bolts to the specified torque. After tightening, mark the bolt head and the adjacent fastened surface with a visible line. This provides a quick visual reference to detect any bolt rotation. If a bolt loosens, it should be gradually retightened in the tightening direction until the mark on the bolt head realigns with the mark on the surface.

Ensure Perpendicular Alignment to Prevent Eccentric Loading

The axis of the bolt hole must be perpendicular to the mounting surface to prevent uneven tensile deformation during tightening, which can lead to localized plastic strain. Over-tightening beyond the material’s yield strength can cause necking, where stress concentrates until it reaches the tensile strength limit, leading to a rapid decrease in load capacity and eventual bolt fracture. Correct alignment and proper torque control are essential to avoid this.

Reduce Hydraulic Shocks and System Vibration

Minimizing hydraulic shocks helps prevent pipe clamp bolts from loosening. Install corrugated compensators in rigid piping to dampen vibration. Flexible mounting solutions can also be employed. For large excavators, use pipe clamp fixing seats designed with high damping capacity, employing a combination of rigid and flexible fixing methods to absorb dynamic loads.

Mitigate System-Induced Vibration

The hydraulic system generates vibration during startup and shutdown, which can affect bolt security. To address this, install one-way throttle valves in the boom descent and arm retraction circuits. Poor coordination within the hydraulic system should be rectified by optimizing system components, such as adjusting main valve specifications, resizing priority valve throttle orifices, and fine-tuning solenoid valve parameters to ensure smoother operation and reduce vibration transmission.