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The wear limit of crane hooks should be determined based on the size change of the dangerous section (usually the part of the hook mouth or hook neck with the greatest force). The specific standards are as follows:

1. General scrapping standards (GB/T 10051, ISO 2415, etc.)

• Hook mouth (opening degree) wear :

  • It shall not exceed 10% of the original size (for example, the original hook width is 100mm, and after wear it is ≤110mm).

  • If the hook is used for frequent operations or high-risk situations (such as metallurgy and chemical industry), stricter restrictions (such as 5% ) are recommended.

• Wear of dangerous section (hook body or hook neck) :

  • The wear depth shall not exceed 5% of the original size (for example, the original section diameter is 40mm, and after wear it is ≥38mm).

  • If the wear causes the cross-sectional area to decrease by more than 10% (for example, a 5% decrease in diameter corresponds to a decrease in cross-sectional area of approximately 10%), it must be scrapped.

2. Additional requirements for different hook types

• Forged single hook : focus on checking the wear on the hook neck (AA section) and the inside of the hook tip.

• Plate hook (laminated type) : A single steel plate needs to be replaced when the wear exceeds 5% of the thickness or cracks appear.

• Anti-unhooking device : When auxiliary parts such as spring locks and tongues fail due to wear, they need to be repaired or scrapped.

3. Strict requirements for special working conditions

• High temperature and corrosive environment : The wear limit needs to be further reduced (e.g. 3%~5% ), and the corrosion reduction should be checked regularly.

• Frequent impact loads : Even if the wear is within the limit, if hardening or microcracks appear on the surface, it should be replaced in advance.

4. Detection Methods

• Caliper measurement : Compare with design drawings or factory calibrated dimensions.

• Ultrasonic thickness gauge : Precise assessment of remaining thickness (especially plate hooks).

• Magnetic particle inspection : Check whether the worn parts are accompanied by cracks.

Example Calculation

If the original diameter of the dangerous section of the hook is  50mm :

• Minimum allowable diameter  = 50mm × (1 - 5%) =  47.5mm

• If worn to 47mm (reduced by 6%) : it has exceeded the standard and needs to be scrapped.

Key Tips

1. Uneven wear : If the local wear depth exceeds the limit (such as a pit on one side of the hook tip), the hook may be scrapped even if the overall wear depth does not exceed 10%.

2. Repair by welding is prohibited : hooks with excessive wear must be replaced. Welding will change the material properties and cause the risk of breakage.

3. Regular inspection : Measure the wear at least once every quarter. The cycle should be shortened in high-frequency use.

Safety principle : When the wear is close to the limit or there is doubt, it should be scrapped first and "make do with it" is strictly prohibited!