Inspection methods, procedures and precautions for cranes (crane trucks)

2026年7月20日

Crane is an indispensable lifting equipment in fields such as construction engineering, equipment installation, municipal emergency rescue, and logistics hoisting. It is mounted on a general or specialized vehicle chassis and integrates a rotating platform, telescopic boom, lifting winch, luffing cylinder, and hydraulic electrical control system to achieve mobile lifting operations. The operation of cranes has an extremely high risk level - incidents such as broken steel wire ropes, bent boom, failure of the slewing bearing, and vehicle overturning are all potential triggers for mass casualties and significant property losses. In scenarios such as new machine delivery, second-hand transactions, inspection of leased equipment upon lease termination, and annual mandatory inspections, a systematic inspection covering structural components, lifting and luffing, slewing systems, safety devices, and hydraulic electrical systems is a core barrier for ensuring the inherent safety of equipment and the value of assets.
I. Overview of Inspection Methods
Based on the rated lifting capacity of the truck crane, the boom type (extendable arm / truss arm), the leg type (H type / X type), and the client's requirements, the inspection will comprehensively employ the following methods:
Static comprehensive inspection: The vehicle is left stationary. The chassis frame, leg system, slewing bearing, boom system, steel wire rope, hook, pulley group, hydraulic pipelines, electrical system, etc. are inspected item by item through visual inspection, hand touch, and measurement with measuring tools.
Dynamic performance test: Conduct tests of lifting, slewing, telescoping, rotation, and leg retraction and extension on a safe site to verify the smoothness, speed, and control response of each working mechanism's movement.
Load test: Using standard weights or known masses, the lifting capacity, structural stiffness, and effectiveness of safety devices of the crane under the rated load are verified. This is the core part of the test and cannot be omitted.
Special verification of safety devices: Trigger and test all safety functions one by one, including torque limiter, over-pull protection, over-discharge protection, amplitude limit, leg interlock, and emergency stop.
Document and label traceability: Verify the consistency and validity of the entire machine's label, chassis VIN code, boom label, wire rope certificate, safety device calibration report, special equipment usage registration certificate, and regular inspection report.
The third-party inspection consists of a complete package including "static full inspection + dynamic performance testing + safety device verification + load test + in-depth document review".
II. Inspection Process
1. Data Collection and Preparation for Inspection
The client provides a list of the vehicles to be inspected, specifying the manufacturer, model, maximum rated lifting capacity, number and length of the boom sections, leg type, counterweight configuration, working hours, applicable standards (GB/T 3811, GB 6067.1, TSG Q7015, etc.). The inspector prepares: long tape measure/ laser distance meter, vernier caliper, feeler gauge, wire rope diameter gauge, ultrasonic thickness gauge, hydraulic pressure gauge set, infrared thermometer, level gauge, walkie-talkie, calibrated weights or heavy objects, etc.
2. Confirmation of venue and safety conditions
The loading test site must be solid and flat. The bearing capacity of the foundation beneath the outriggers must meet the requirements for the maximum outrigger reaction force. If necessary, steel plates or roadbed boxes should be laid. The radius of the test site should be no less than the maximum working radius of the crane plus the safety margin. There should be no overhead cables above the site. A double warning line should be set up in the inspection area, and non-inspection and command personnel are strictly prohibited from entering. The lifting commander and the test driver must hold valid special equipment operation qualification certificates. A unified command signal and emergency plan should be established.
3. Identity and Label Verification
Vehicle nameplate: Verify that the manufacturer, model, factory serial number, manufacturing date, rated lifting capacity, working range, etc. are consistent with those in the "Special Equipment Use Registration Certificate".
Chassis VIN code: Impress the VIN code of the frame, compare it with the certificate of conformity and the driving license, and check for any signs of grinding or tampering.
Lifting arm nameplate: The nameplate information on each telescopic arm is consistent with that of the entire machine.
Main assembly nameplates/serial numbers: Record of nameplates or serial numbers for key assemblies such as the engine, lifting winch, slewing reducer, luffing cylinder, and telescopic cylinder.
Wire rope certificate: Wire rope manufacturer, model, diameter, breaking tension and factory certificate of conformity, confirming its validity within the usage period.
Special equipment procedures: Are the "Special Equipment Use Registration Certificate" and "Periodic Inspection Report" within their validity periods? If the procedures are incomplete or have expired, they must be upgraded to a serious non-compliance item.
4. Inspection of the chassis and leg system - The foundation of stability
Chassis frame: The main beam is inspected from front to back with strong light, focusing on checking for cracks or performing welding repairs in the areas where the slewing bearings are installed, the leg connections, and the counterweight suspension. The connecting bolts between the auxiliary beam and the main beam are tightened.
Legs: The H-shaped/X-shaped leg box structures show no deformation, cracking or welding repairs. The leg extension movements are smooth, and the mechanical locking pins are reliably inserted after full extension. The coating on the piston rods of the vertical leg cylinders shows no damage, and the hydraulic locking function is effective. The leg foot plates are intact, and the connecting pin shafts are firmly secured.
Level gauge and leg status indicator: The level gauge in the cab is functioning properly, and the indicator light for the leg extension is consistent with the actual situation.
Suspension locking: The rear axle suspension locking device (if present) functions effectively during heavy lifting operations.
5. Rotation system inspection - The core assembly that supports the rotation
Swivel support: Check the tightening of connecting bolts between the inner and outer rings and the upper and lower vehicle frames. The tooth surfaces of the gear rings show no broken teeth or severe wear. The sealing strips are intact and do not come off. During operation, listen throughout for any "clicking" abnormal sounds. If such sounds are detected, they must be recorded as an early warning.
Rotation mechanism: The rotation motor/brake gear housing shows no oil leakage, and the braking function is effective.
Center rotary joint: The hydraulic center rotary body shows no leakage, and the electrical slip ring (if present) functions properly.
6. Arm Frame System Inspection - The Arm of Power
Arm appearance: There are no collision depressions or severe rust on the surface of each arm section. The weld heat affected zone is the focus - the arm head, arm tail, edge of the reinforcing plate, and welds of the telescopic slider seat. Use a strong light flashlight to inspect the surface for cracks.
Extension mechanism: The extension cylinder operates smoothly, and the sequence of extending and retracting each level of the boom is correct. The gap between the sliding block of the extension arm and the wear-resistant pad is measured using a feeler gauge.
Lift arm straightness: In the fully extended state, visually inspect or use a string method to check for lateral deviation of the arm head. There should be no permanent deformation caused by overload.
Lifting mechanism: Measurement of the clearance between the ear seat pin and the lifting cylinder in the full stroke shows no leakage. Function of the balance valve - when the valve is in the neutral position, the boom should stop reliably without any significant downward movement.
7. Hoisting system and inspection of steel wire ropes/hooks
Lifting winch: The base bolts are tightened. The reducer has no oil leakage and operates without abnormal noise. The brake is responsive in opening and closing, and the wear of the friction plates is checked. The condition of the rope groove on the drum, and the arrangement of the steel wire rope are neat.
Steel wire rope: Measure the entire length with a diameter gauge at multiple points. The wear shall not exceed 7% of the nominal diameter. If the number of broken wires in one lay length reaches the scrap standard stipulated in GB/T 5972, it shall be immediately scrapped. Check for broken strands, twists, rust, and rope core extrusion. The rope end is securely fixed.
Pulley system: All pulleys rotate smoothly. The rope grooves have been measured using a caliper and the anti-detachment rope device is in good condition.
Hook: The surface is free from cracks. The deformation of the opening is no more than 15% of the original size. The anti-detachment hook spring is effective and the rotation is smooth.
8. Inspection of Hydraulic and Electrical Systems
Hydraulic system: There is no leakage in the main pump/valve group/pilot system. All hoses are inspected one by one for aging, cracking and bulging. The hoses inside the boom and near the hinge points are particularly checked for interference and wear. The oil tank level and oil quality are checked. After the load test, a comprehensive recheck is conducted to ensure no new leaks at the joints.
Electrical system: Functions of the control room instruments and displays for boarding and alighting are normal. There are no fault codes for the torque limiter. The length/angle/rotation angle sensors of the arm are in good condition. The operation lights, outline lights, rotation warning lights, and buzzer functions are all effective.
9. Special verification of safety devices - Every protection measure must be tested in reality.
Torque limiter: Gradually increase the amplitude during the load test to verify the overload warning and automatic disconnection function in dangerous directions, and record the trigger point load and amplitude.
Overload/over-discharge protection: Slowly raise/lower the hook to the extreme position, and verify that the protection is triggered and an alarm is sounded.
Amplitude limit: Verification of limit protection for boom extension and retraction as well as for the upper and lower limit positions of the luffing action.
Leg interlock: Multi-condition verification of the interlock logic between the leg status and the boom movement.
Emergency Stop: The engine will shut off or the power source will be cut off after the up/down vehicle stop buttons are pressed.
10. Dynamic performance and load test
No-load test run (before load test):
The lifting, slewing, telescoping and rotation operations are all performed at full speed and with smooth micro-motion, and the combined actions are coordinated.
The outriggers were retracted and extended twice, and the locking was secure.
Rated load test:
Select two typical working ranges. Lift the corresponding rated load and hover 200mm above the ground.
The structural deflection was checked and found to be normal. The legs did not lift up.
The lifting, rotation and luffing actions are reliably braked, and the heavy load does not slide down.
Hover for at least 5 minutes and measure the amount of weight that sinks.
Static load test (as per the contract agreement, usually 1.25 times the rated load):
Slowly lift 1.25 times the load, hover 100-200mm off the ground for at least 10 minutes.
Verify the structural strength and stability. After unloading, conduct a comprehensive re-inspection of the structural components to ensure there is no permanent deformation or new cracks.
Dynamic load test (as per the contract, usually 1.1 times the rated load):
Lift the load by 1.1 times and complete all the actions to verify the dynamic braking performance.
11. Comprehensive re-inspection after the test
After the load test, a recheck must be conducted: the key welds of the boom, the bolts and gear rings of the slewing bearing, the legs and locking mechanism, all hydraulic connectors and cylinder seals, the steel wire ropes and the condition of the hooks.
12. Report Output
Summarize all inspection records, load test data, safety device test list, and image materials to form the "Third-party Crane (Crawler Crane) Inspection Report". The report must clearly state the test results of each safety device, and attach photo evidence for non-compliant items. The names and certificate numbers of the inspectors, crane operators, and test drivers are recorded.
III. Important Notes
Safety is the supreme principle for evaluating the operation.
Before conducting any load test, it is necessary to confirm the ground's bearing capacity. This can be determined by calculating the maximum reaction force of the outriggers and deciding whether auxiliary pads are required.
Inspectors must absolutely not stand beneath the lifted object, below the boom rotation plane, or within the dangerous fan-shaped area prone to overturning.
The torque limiter and over-pull protection must undergo initial verification under no-load or low-load conditions before conducting the large-load test. It is strictly prohibited to conduct overload tests when the protection has not been confirmed to be effective.
When any abnormal noise, signs of structural deformation or precursors of hydraulic pipe rupture occur, immediately stop and unload for inspection.
The determination of when a steel wire rope should be scrapped must be strict.
The steel wire rope is the last line of defense for lifting safety. Any wire rope that meets the报废 standard stipulated in GB/T 5972 must be judged as unqualified. This criterion is not influenced by subjective perceptions such as "it seems still usable". The dry and rusted condition of the wire rope lubrication must also be included in the observation items.
Structural component cracks are fatal defects.
The cracks in the boom, the swivel support seat ring, the leg box, and the connection area of the frame are all critical defects. During the inspection, use a strong light to scan all key weld seams slowly. Any suspected cracks must be cleaned and then undergo PT/MT flaw detection for confirmation. The repaired structural components that have been re-welded must have their repair records (process, welding qualifications, flaw detection reports) traced back, otherwise, a downgrade assessment will be conducted.
Safety devices are "invisible protectors".
Any failure of a safety device (especially the torque limiter, over-pull protection, and leg interlock) is a major and fatal hazard. The inspector must witness the alarm being triggered and confirm the automatic disconnection of the action with their own eyes. They cannot rely solely on verbal confirmation.
The compliance of special equipment is the bottom line for inspection.
Crane trucks are classified as special equipment. The "Special Equipment Use Registration Certificate" and the "Periodic Inspection Report" must be valid. If they are used without a certificate or fail to undergo regular inspections beyond the expiration date, such situations should be clearly identified as major management deficiencies in the report and the legal risks should be warned.
The photographic archives are the vitality of the inspection conclusion.
Close-up of broken steel wire strands, measurement of the opening degree of the hook with a caliper, photos of the cracked parts of the structural components, display of the instrument at the moment the safety device is triggered, the contact state of the legs with the ground during the load test, the timer for the suspended load, etc. Each non-conformity determination should be supported by photos or videos.