Crane Inspection and Maintenance Intervals per GB/T 31052.3

GB/T 31052.3-2014 is Part 3 of the GB/T 31052 series on inspection and maintenance procedures, specifically addressing mobile cranes. Unlike overhead type cranes, mobile cranes are self-propelled and frequently relocated between job sites, which means their structural configuration and working condition change with each move—boom extension/retraction, outrigger deployment, and slewing mechanism operation all take a toll. The inspection and maintenance focus therefore differs significantly from that of overhead type cranes. The standard applies to the inspection and maintenance of all types of mobile cranes and serves as a key reference for safety management at construction sites. Kelude Heavy Industry provides periodic inspection services for mobile cranes in accordance with this standard.

Daily Inspection Checklist for Mobile Cranes

The standard specifies that daily inspections of mobile cranes are performed by the operator before each shift and after work is completed. Pre-start inspection items include: the chassis—tire pressure and tread wear (tread depth must not be less than 1.6 mm), outrigger structure and hydraulic system for leaks, and outrigger pads for stable ground contact. The boom—smooth extension/retraction without abnormal noise, no visible deformation or cracks on the boom surface, and no leaks from the telescoping cylinder. The hoisting mechanism—main and auxiliary hooks free of cracks or deformation, Hook Latch in good working order, wire rope properly spooled on the drum, and no broken wires or wear on the rope. The slewing mechanism—no loose connection bolts on the Slewing Bearing and no abnormal noise from the slewing drive.

Safety device checks are the priority of the daily inspection. The Load moment limiter (LML) (overload protection device) should display normal readings during the power-on self-test, with all sensor wiring harnesses intact. The Height Limit Switch (anti-over-hoisting device) should function correctly—it must trigger an alarm and cut hoisting power when the hook approaches its upper limit. The Radius Limit Switch should activate an alarm when the boom extends to its maximum radius. The spirit level (chassis level indicator) should provide accurate readings, with the levelness deviation of the entire machine in both longitudinal and transverse directions not exceeding 1° after the outrigger pads contact the ground. All Control Grips and pedals should respond promptly and return to neutral properly. Pressing the Emergency Stop Button must bring all mechanisms to an immediate halt. Post-shift inspections should focus on: abnormal temperature rise or leaks in the engine and hydraulic system, reliable braking of all mechanism brakes, and proper shutdown of the LML display screen.

Periodic and Thorough Inspection Requirements

Periodic inspections are carried out quarterly or every 500 operating hours (whichever comes first) by maintenance technicians. These inspections cover all daily inspection items plus additional checks: professional engine and hydraulic system evaluation—engine oil and filter element replacement, hydraulic oil sampling and analysis, and noise and temperature rise testing of hydraulic pumps and motors. Visual inspection of boom weld seams—using a magnifying glass of at least 5× power to examine the connection welds between the main chord members and web plates on each boom section. Full-length wire rope examination—the rope end connections are detached to allow a complete inspection, with particular attention to the condition of the rope core and internal corrosion. Slewing bearing gear backlash measurement—using a feeler gauge or dial indicator to check the Backlash and record the values against the baseline data. Outrigger structure weld and pivot point inspection—checking the mounting base welds on the outrigger horizontal beams and vertical cylinders for cracks. Electrical system insulation test—the Insulation Resistance of the entire machine must not be less than 1 MΩ.

A thorough examination is conducted annually by an equipment engineer or a qualified third-party inspection agency. In addition to all periodic inspection items, the thorough examination includes: boom extension/retraction test—measuring the Side bow / lateral bow of each boom section in both fully extended and fully retracted positions, with at least 3 complete extension/retraction cycles performed without any sticking. No-load operational test of the complete machine—each mechanism is operated at rated speed for no fewer than 10 cycles without any abnormalities. Rated Load Test (100% SWL)—the rated load is lifted at various typical working radii to verify overall stability and measure brake slip distance. Dynamic Load Test—1.1 times the rated load is lifted and operated at maximum mechanism speeds for no fewer than 5 cycles. Static load test—1.25 times the rated load is lifted and held stationary at the maximum working radius for 10 minutes. Structural flaw detection—Ultrasonic Testing (UT) is performed on critical weld seams, including the boom base, Slewing Bearing connections, and outrigger pivot points. Load moment limiter (LML) accuracy calibration—using Standard Weights at various typical radii, with a maximum permissible error of ±5%.

Inspection Records and Documentation Management

The standard requires that inspection results for mobile cranes be accurately recorded and archived. Daily inspection entries are logged in the operation log and retained for at least one year. Periodic and thorough examinations produce formal inspection reports that are filed in the equipment's technical documentation and kept until the crane is scrapped. Each inspection report includes basic equipment information (model, serial number, current operating hours), a detailed breakdown of inspection items and results, a description of any identified issues along with corrective actions taken, and a recommended date for the next inspection. Class A nonconformities — defects that pose an immediate safety risk, such as a failed load moment limiter (LML), cracks in the jib, or excessive wire rope breakage — require the crane to be taken out of service immediately, with operation prohibited until rectification is complete. Class B nonconformities, which do not affect safety but require timely correction, must be documented in the inspection report with a specified rectification deadline and follow-up tracking.

The technical documentation for a mobile crane must travel with the equipment — whenever the crane is relocated to a new jobsite, the documentation moves with it. At a minimum, the documentation must include: the Factory Certificate and technical files, the Installation Acceptance Report, all prior periodic inspection reports, records of major repairs and retrofits, incident records, and LML calibration records. Operator changes must be logged in the documentation with handover details. If the crane has been out of service for more than six months, a thorough examination is required before it can be returned to service. When the crane is scrapped, the technical documentation must be either destroyed or archived for future reference. The standard also recommends that user units implement a digitalized equipment management system to archive all inspection records electronically, enabling efficient retrieval and trend analysis of the crane's long-term operating condition.

Jib and Wire Rope Special Inspection

The jib and wire rope are at the core of mobile crane inspection and maintenance. The standard sets specific requirements for inspecting the telescoping mechanism: the piston rod surface of the telescoping cylinder must be free of scoring and corrosion, the cylinder seal rings must show no leakage, and the tension on the telescoping wire rope or chain must be evenly distributed. Wear pads between boom sections must be replaced when their thickness has worn by more than 50% of the original dimension, and the clearance should be adjusted to the design value (typically 0.5–2.0 mm). During boom extension/retraction, the operator should verify that each section extends in the correct sequence — an abnormal sequence may indicate an internal fault in the telescoping mechanism. The side bow of the fully extended boom must not exceed 1/1000 of the boom length. Wire rope inspection intervals for mobile cranes should be more frequent than for overhead type cranes — because the wire rope on a mobile crane is regularly subjected to impact loads and bending fatigue during hoisting operations, a visual inspection is recommended every 100 hours, with a full-length inspection performed monthly. The rope must be replaced when the number of broken wires within one lay length exceeds 10% of the total wire count, or when diameter wear exceeds 7% of the original diameter. The clamping plate or wedge securing the wire rope to the drum should be checked quarterly to confirm that the fastening remains secure. Kelude Heavy Industry uses professional wire rope detectors in its inspection services to identify internal damage in mobile crane wire ropes, providing early warning of hidden defects so replacement can be scheduled before failure occurs.

Mobile Crane Inspection Checklist Reference

The comparison table below outlines the core parameters and configurations for mobile crane inspection items, for reference by selection and operation personnel.

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