Failure modes and preventive measures of crane hooks-Weihua Crane

Failure modes and preventive measures of crane hooks

2025-07-29 01:10:52

The failure modes of crane hooks directly affect the safety of operations, and targeted preventive measures need to be taken . The following are the main failure modes and corresponding prevention plans:

1. Common failure modes and cause analysis

1. Plastic deformation (permanent bending)

reason :
- Overloading (exceeding the rated load).
- Material fatigue or improper heat treatment leads to loss of strength.
Symptoms : The hook opening becomes larger or the hook body bends and cannot be restored.

2. Cracks and fractures

reason :
- Long-term alternating loads induce fatigue cracks (commonly seen at the base of the hook neck).
- Manufacturing defects (e.g. internal pores, inclusions).
- Brittle fracture of materials in low temperature environment.
Symptoms : Cracks are visible on the surface, and fractures often occur in high stress areas.

3. Excessive wear

reason :
- Friction between the rope/chain and the hook (especially if there is no wear pad).
- Superposition of corrosion and wear (chemical industry, marine environment).
Symptoms : The thickness of the hook tip or the load-bearing surface is reduced, and the cross-sectional bearing capacity is reduced.

4. Failure of the anti-unhooking device

reason :
- The tongue is deformed, the spring is broken or removed manually.
- Improper closure causes the sling to unhook.

5. Failure of connection parts

reason :
- Pins are worn, bolts are loose or broken.
- The pulley block bearing is stuck, causing abnormal lateral force.

2. Targeted preventive measures

1. Prevention during the design phase

Material selection : Use high-strength alloy steel such as DG20Mn , and cold-resistant steel for low-temperature environments .
Process control : Tempering heat treatment after forging to avoid stress concentration structure.
Safety factor : Design minimum breaking load according to standards (such as ISO 8754) ≥ 4 times rated load.

2. Prevention during use

Overloading is strictly prohibited : install a load limiter to automatically cut off power when overloaded.
Regular testing :
- Magnetic particle inspection (check for cracks, once every 6 months).
- Wear monitoring (caliper measurement, replace if wear ≥5%).
Environmental protection :
- In corrosive environments, use galvanized hooks or apply anti-rust oil regularly.
- Heat-resistant steel hooks should be used in high-temperature places.

3. Maintenance and operation specifications

Lubrication and maintenance : Add high-temperature grease to the bearing every 500 hours.
Anti-unhooking device : Check the closing status of the tongue every shift and replace it immediately if damaged.
Operation training : It is forbidden to pull obliquely or sideways, and to avoid impact loads.

4. Scrap standards (GB/T 10051.1)

Cracks or breaks (of any size).
The opening increases by > 10% of the original size.
Dangerous section wear > 5% or thread failure.

3. Failure Case Analysis

Case 1 : A hook break accident at a port
- Reason : Fatigue cracks were not detected + salt spray corrosion accelerated its expansion.
- Lesson : Need to increase the frequency of NDT and use stainless steel hooks instead.
Case 2 : Unhooking during lifting
- Cause : The anti-slip tongue spring rusted and failed, causing the sling to slip.
- Improvements : Check tongue elasticity weekly and shorten rainy season to 3 days.

IV. Conclusion

Through the triple control of design optimization + strict testing + standardized operation , the risk of hook failure can be effectively reduced. Key points:

Overloading is the number one killer – load limiting devices must be installed.
Fatigue cracks are highly hidden – rely on regular non-destructive testing.
Small parts, big risks - anti-unhooking devices need to be included in daily inspections.

It is recommended to combine Internet of Things technology (such as installing strain sensors) to monitor the hook status in real time and achieve predictive maintenance.

1. Common failure modes and cause analysis

1. Plastic deformation (permanent bending)

reason :
- Overloading (exceeding the rated load).
- Material fatigue or improper heat treatment leads to loss of strength.
Symptoms : The hook opening becomes larger or the hook body bends and cannot be restored.

2. Cracks and fractures

reason :
- Long-term alternating loads induce fatigue cracks (commonly seen at the base of the hook neck).
- Manufacturing defects (e.g. internal pores, inclusions).
- Brittle fracture of materials in low temperature environment.
Symptoms : Cracks are visible on the surface, and fractures often occur in high stress areas.

3. Excessive wear

reason :
- Friction between the rope/chain and the hook (especially if there is no wear pad).
- Superposition of corrosion and wear (chemical industry, marine environment).
Symptoms : The thickness of the hook tip or the load-bearing surface is reduced, and the cross-sectional bearing capacity is reduced.

4. Failure of the anti-unhooking device

reason :
- The tongue is deformed, the spring is broken or removed manually.
- Improper closure causes the sling to unhook.

5. Failure of connection parts

reason :
- Pins are worn, bolts are loose or broken.
- The pulley block bearing is stuck, causing abnormal lateral force.

2. Targeted preventive measures

1. Prevention during the design phase

Material selection : Use high-strength alloy steel such as DG20Mn , and cold-resistant steel for low-temperature environments .
Process control : Tempering heat treatment after forging to avoid stress concentration structure.
Safety factor : Design minimum breaking load according to standards (such as ISO 8754) ≥ 4 times rated load.

2. Prevention during use

Overloading is strictly prohibited : install a load limiter to automatically cut off power when overloaded.
Regular testing :
- Magnetic particle inspection (check for cracks, once every 6 months).
- Wear monitoring (caliper measurement, replace if wear ≥5%).
Environmental protection :
- In corrosive environments, use galvanized hooks or apply anti-rust oil regularly.
- Heat-resistant steel hooks should be used in high-temperature places.

3. Maintenance and operation specifications

Lubrication and maintenance : Add high-temperature grease to the bearing every 500 hours.
Anti-unhooking device : Check the closing status of the tongue every shift and replace it immediately if damaged.
Operation training : It is forbidden to pull obliquely or sideways, and to avoid impact loads.

4. Scrap standards (GB/T 10051.1)

Cracks or breaks (of any size).
The opening increases by > 10% of the original size.
Dangerous section wear > 5% or thread failure.

3. Failure Case Analysis

Case 1 : A hook break accident at a port
- Reason : Fatigue cracks were not detected + salt spray corrosion accelerated its expansion.
- Lesson : Need to increase the frequency of NDT and use stainless steel hooks instead.
Case 2 : Unhooking during lifting
- Cause : The anti-slip tongue spring rusted and failed, causing the sling to slip.
- Improvements : Check tongue elasticity weekly and shorten rainy season to 3 days.

IV. Conclusion

Through the triple control of design optimization + strict testing + standardized operation , the risk of hook failure can be effectively reduced. Key points:

Overloading is the number one killer – load limiting devices must be installed.
Fatigue cracks are highly hidden – rely on regular non-destructive testing.
Small parts, big risks - anti-unhooking devices need to be included in daily inspections.

It is recommended to combine Internet of Things technology (such as installing strain sensors) to monitor the hook status in real time and achieve predictive maintenance.

1. Common failure modes and cause analysis

1. Plastic deformation (permanent bending)

reason :
- Overloading (exceeding the rated load).
- Material fatigue or improper heat treatment leads to loss of strength.
Symptoms : The hook opening becomes larger or the hook body bends and cannot be restored.

2. Cracks and fractures

reason :
- Long-term alternating loads induce fatigue cracks (commonly seen at the base of the hook neck).
- Manufacturing defects (e.g. internal pores, inclusions).
- Brittle fracture of materials in low temperature environment.
Symptoms : Cracks are visible on the surface, and fractures often occur in high stress areas.

3. Excessive wear

reason :
- Friction between the rope/chain and the hook (especially if there is no wear pad).
- Superposition of corrosion and wear (chemical industry, marine environment).
Symptoms : The thickness of the hook tip or the load-bearing surface is reduced, and the cross-sectional bearing capacity is reduced.

4. Failure of the anti-unhooking device

reason :
- The tongue is deformed, the spring is broken or removed manually.
- Improper closure causes the sling to unhook.

5. Failure of connection parts

reason :
- Pins are worn, bolts are loose or broken.
- The pulley block bearing is stuck, causing abnormal lateral force.

2. Targeted preventive measures

1. Prevention during the design phase

Material selection : Use high-strength alloy steel such as DG20Mn , and cold-resistant steel for low-temperature environments .
Process control : Tempering heat treatment after forging to avoid stress concentration structure.
Safety factor : Design minimum breaking load according to standards (such as ISO 8754) ≥ 4 times rated load.

2. Prevention during use

Overloading is strictly prohibited : install a load limiter to automatically cut off power when overloaded.
Regular testing :
- Magnetic particle inspection (check for cracks, once every 6 months).
- Wear monitoring (caliper measurement, replace if wear ≥5%).
Environmental protection :
- In corrosive environments, use galvanized hooks or apply anti-rust oil regularly.
- Heat-resistant steel hooks should be used in high-temperature places.

3. Maintenance and operation specifications

Lubrication and maintenance : Add high-temperature grease to the bearing every 500 hours.
Anti-unhooking device : Check the closing status of the tongue every shift and replace it immediately if damaged.
Operation training : It is forbidden to pull obliquely or sideways, and to avoid impact loads.

4. Scrap standards (GB/T 10051.1)

Cracks or breaks (of any size).
The opening increases by > 10% of the original size.
Dangerous section wear > 5% or thread failure.

3. Failure Case Analysis

Case 1 : A hook break accident at a port
- Reason : Fatigue cracks were not detected + salt spray corrosion accelerated its expansion.
- Lesson : Need to increase the frequency of NDT and use stainless steel hooks instead.
Case 2 : Unhooking during lifting
- Cause : The anti-slip tongue spring rusted and failed, causing the sling to slip.
- Improvements : Check tongue elasticity weekly and shorten rainy season to 3 days.

IV. Conclusion

Through the triple control of design optimization + strict testing + standardized operation , the risk of hook failure can be effectively reduced. Key points:

Overloading is the number one killer – load limiting devices must be installed.
Fatigue cracks are highly hidden – rely on regular non-destructive testing.
Small parts, big risks - anti-unhooking devices need to be included in daily inspections.

It is recommended to combine Internet of Things technology (such as installing strain sensors) to monitor the hook status in real time and achieve predictive maintenance.

Pre: Specification for multi-machine collaborative operation of crane hooks

Next: Daily Inspection Checklist for Crane Hooks

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