As Part 6 of the GB/T 31052 series, this standard focuses specifically on the inspection, maintenance, and hydraulic system testing requirements for mobile cranes.

Standard Scope and Inspection Framework

GB/T 31052.6-2020 is the sixth part of the GB/T 31052 series. The key difference between mobile cranes and fixed base cranes in terms of inspection and maintenance is that mobile cranes incorporate an engine, chassis, and hydraulic system—components absent in fixed base cranes—while the outrigger system and boom telescoping mechanism are the most failure-prone areas. The standard establishes a four-tier inspection and maintenance system: daily inspection (performed by the operator before each shift), first-level maintenance (monthly, by qualified maintenance personnel), second-level maintenance (quarterly), and annual comprehensive inspection (by a certified inspection body). A complete equipment file must be maintained for each mobile crane, documenting the date, findings, issues identified, and corrective actions for every inspection.

Daily Inspection (Pre-Shift)

Before each shift, the operator must check the following items: Hydraulic system—hydraulic oil level between the high and low marks on the sight gauge, no leaks in hoses or fittings, and no signs of oil contamination or emulsification. Outrigger system—outriggers extend and retract smoothly without binding, and the hydraulic lock valve functions properly (with outriggers extended and the engine shut off, the 24-hour settlement must not exceed 10 mm). Jib system—boom extends and retracts smoothly without abnormal noise, and wear on the slide pads (wear plates) does not exceed 50% of the original thickness. Hoisting mechanism—brake functions correctly (test by lifting the hook 100 mm off the ground to confirm no load slipping), wire rope is properly spooled on the drum, and at least 3 safety wraps remain on the drum. Safety devices—load moment limiter (LML) passes its self-test, height limit switch is functionally tested, and horn and lights are operational. Tires (truck cranes)—proper inflation pressure and all bolts are tight. Tracks (crawler cranes)—proper tension and no cracks in the track links.

Periodic Inspection and Maintenance

First-level maintenance (monthly / every 250 hours)—engine oil and filter element replacement, hydraulic oil return filter element replacement, re-torquing of slewing bearing bolts (20% sampled, torque ≥90% of specified value), load moment limiter accuracy calibration (verified with standard test weights, deviation ≤±5%), and greasing of all mechanisms per the lubrication chart. Second-level maintenance (quarterly / every 750 hours)—hydraulic oil sampling and analysis (acid value, moisture, viscosity, and particle count NAS ≤9), gearbox lubrication oil replacement, full-length inspection of the boom telescoping wire rope (scrap if wire breaks in one lay length exceed 5% of the total wire count), and measurement of slewing bearing raceway clearance (radial clearance measured with a dial indicator ≤0.5 mm). Annual inspection—hydraulic system pressure testing (verification of safety valve set points), MT spot-checking of structural weld seams (boom root, outrigger weld areas, and slewing platform), and load testing (static load at 1.25× rated capacity plus dynamic load at 1.1× rated capacity).

Boom Telescoping Mechanism Inspection

The boom telescoping mechanism is one of the highest failure-rate components on mobile cranes. The standard requires focused inspection of the following: Slide pad (wear plate) wear—the guide pads and wear plates between boom sections must be inspected monthly; replacement is mandatory when wear exceeds 50% of the original thickness. Boom telescoping wire rope—this is the most commonly overlooked component with the most severe failure consequences; a broken telescoping rope can prevent the boom from retracting or cause sudden uncontrolled retraction. Inspection method: with the boom fully retracted, check the exposed rope section for wire breaks and corrosion; during telescoping, inspect the rope segments passing through the boom section ports section by section. Telescoping hydraulic cylinder—scratches deeper than 0.2 mm on the cylinder barrel wall require replacement, and oil seal leaks must be addressed promptly. Any wire breaks found in the telescoping rope require immediate replacement; continued use is not permitted.

Mobile Crane Inspection & Maintenance Reference Table

The reference table below summarizes the core parameters and configurations for mobile crane inspection and maintenance, serving as a quick guide for operators and maintenance personnel.

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Frequently Asked Questions