company news about Safety load limit of hook and daily inspection points

As a key component of crane equipment, the performance of the hook directly affects the safety of hoisting operations. In 2024, in the "7.15" accident in Shekou, Shenzhen, the deformation of the bolts of the auxiliary hook locking device was not discovered in time, causing the sling to fall off and hit the worker. In the same year, in the "5.16" accident in Guangzhou, the long-term failure to inspect the lifting height limiter caused the hook to fall. Such accidents warn us that safety inspections, load limits, and defect handling of hooks are extremely important. The failure of the hook may cause significant casualties and property losses.

Key factors affecting carrying capacity

1、Material fatigue and environmental corrosion

The hook is subjected to alternating loads for a long time, and micro cracks are prone to appear in dangerous sections such as the hook tip and hook neck. In a high temperature environment (such as 200-400℃), the maximum working load of the S (6) grade hook may drop to 75% of that at room temperature; the acidic corrosive environment will accelerate metal corrosion, and stainless steel materials or special coatings are required for protection.

2、Geometric deformation and defect accumulation

When the hook opening exceeds the original size by 15% and the dangerous section wears by 10%, the load-bearing capacity will drop by more than 30%. Magnetic particle inspection shows that the crack growth rate inside the hook cavity can reach 0.1mm/thousand cycles.

3、Special working condition correction

When multiple hooks are hoisted together, the load distribution calculation needs to be used to adjust the load limit of a single hook; in a low temperature environment of -30℃, materials with an impact toughness of ≥27J at -50℃ need to be selected.

Hazards and warnings of exceeding the limit load

Short-term overload may cause plastic deformation of the hook body (such as permanent increase in opening), while long-term overload accelerates metal fatigue. A port crane had a broken hook neck after only 18 months due to long-term overload of 20%. Modern cranes are generally equipped with electronic overload protection devices, which issue an early warning when the load exceeds 90% of the rated value and force a shutdown when it exceeds 110%, realizing intelligent linkage protection with the hook load limit.

Defect treatment and scrapping standards for hooks

1、Specifications for handling repairable defects

Minor wear (<5%) can be repaired by grinding, but it is necessary to confirm that there are no cracks through magnetic particle inspection; the deformation of the shaft pin hole can be restored to size by metal spraying process, and a static load test of 2 times the rated load is required after repair.

2、Forced Deactivation

If cracks, excessive opening, permanent bending of the hook, and other defects are found, the hook must be stopped immediately. In 2024, a power plant failed to deal with the cracks on the hook tip in time, causing the generator stator to break during installation, resulting in direct economic losses of more than 10 million yuan.

3、Scrap determination criteria (based on GB/T 10051.1-2010)

• Dangerous section wear ≥ 10%
• Opening degree increased ≥ 15%
• Hook body plastic deformation cannot be restored
• Cracks still do not meet the requirements of flaw detection after repair

The hook is an important part of the crane operation. Its load-bearing capacity and structural integrity are the key to ensure the safety of the crane. Whether it is short-term or long-term overload use, it may cause catastrophic failure. Please take it seriously.