Failure modes and preventive measures of crane hooks-Weihua Crane

Failure modes and preventive measures of crane hooks

2025-07-30 09:33:41

Failure of a crane hook can lead to serious accidents, so its failure mode must be systematically analyzed and targeted preventive measures taken. The following is a detailed summary of the main failure types, root causes and solutions.

1. Common failure modes and cause analysis

1. Plastic deformation (permanent bending)

Phenomenon : The hook body or hook neck undergoes irreversible bending.
reason :
- Overload : Exceeding the rated load (such as more than 1.5 times the static load).
- Material defect : Inadequate yield strength due to improper heat treatment.
- Shock load : sudden acceleration/stop causes a sudden increase in dynamic stress.

2. Fatigue fracture

Phenomenon : Cracks extend from high stress areas (such as the base of the hook neck) to fracture.
reason :
- Cyclic loading : Frequent lifting leads to cumulative damage (see Miner's law).
- Stress concentration : insufficient design fillet or surface processing defects.
- Corrosive environment : accelerates crack initiation (such as marine salt spray).

3. Brittle fracture

Phenomenon : Sudden fracture without plastic deformation, and the cross section is granular.
reason :
- Low temperature operation : insufficient material toughness (e.g. impact energy < 27J at -20°C).
- Hydrogen embrittlement : Insufficient dehydrogenation after electroplating or pickling.

4. Wear and corrosion

Phenomenon :
- Hook wear : The friction of the sling causes the size to exceed the limit (>10% of the original size).
- Rust penetration : localized corrosion in chemical/marine environments.
reason :
- Insufficient lubrication : Dry friction of rotating parts.
- Failure of protective layer : paint peeling or plating damage.

5. Thread failure (detachable hook)

Phenomenon : Thread slippage, tooth collapse or loose connection.
reason :
- Not tightened according to torque : insufficient or excessive preload.
- Foreign matter intrusion : Dust/rust residue increases wear.

2. Preventive measures

1. Prevention during the design phase

Failure Mode	Design strategies
Plastic deformation	Safety factor ≥ 4 (GB/T 10051), FEA verifies stress distribution under extreme load.
fatigue fracture	Optimize the hook neck transition radius (R≥10mm) and use shot peening to increase the surface compressive stress.
Brittle fracture	Use low-temperature toughness materials (such as 34CrNiMo6) and prohibit electroplating.
Wear/Corrosion	The hook mouth is welded with a wear-resistant layer (such as Hardox 500), and 316 stainless steel is used for marine environment.
Thread failure	Use fine thread + anti-loosening nut (such as Nord-Lock washer).

2. Manufacturing and process control

Material inspection :
- Chemical composition analysis (spectrometer) + mechanical properties test (tensile, impact).
Heat treatment monitoring :
- After the quenching and tempering process (quenching + tempering), the hardness is controlled at HB 200~300.
Non-destructive testing (NDT) :
- 100% magnetic particle testing (MT) to detect surface cracks, and ultrasonic testing (UT) in critical areas.

3. Usage and maintenance measures

Failure Mode	Maintenance measures
Overload deformation	Install a torque limiter to automatically cut off the lifting power supply when overloaded.
Fatigue crack	MT inspection is carried out every 6 months and any cracks found will be scrapped immediately.
Corrosion and wear	Apply anti-rust grease (such as Castrol Rustilo) every month and use plastic sheath in chemical environment.
Loose threads	Check the torque regularly (e.g. M36 bolts require 1200 N·m) and use thread lockers.

4. Personnel training and monitoring

Operation Specifications :
- Oblique pulling and emergency stopping are prohibited, and the sling angle is ≤60°.
Intelligent monitoring :
- Strain sensors are installed to monitor loads in real time, and vibration sensors are used to warn of bearing failures.

III. Typical Cases and Lessons

Case 1: Fatigue fracture accident

Background : A crane hook at a port broke after 5 years of use, causing a container to fall.
Reason : The root of the hook neck was not shot peened and the fatigue crack expanded to a critical size.
Improvement : Make it mandatory to replace the hook every 2 years and add TOFD inspection.

Case 2: Thread slippage causes thread shedding

Background : The hook thread in the metallurgical workshop failed and the ladle tilted.
Cause : The lock nut was not used and the high temperature caused the grease to carbonize.
Improvement : Use high temperature resistant thread locking agent (such as Loctite 272).

4. Failure Analysis Process

On-site protection : Take photos to record the fracture morphology and damaged areas.
Laboratory testing :
- Fracture analysis : SEM scanning electron microscope is used to observe the crack source (such as fatigue striations).
- Metallographic examination : Check for heat treatment defects (such as decarburization layer).
Root cause reporting : Propose design/maintenance improvement plans.

V. Conclusion

Key principles :

Prevention is better than cure : Reduce risk through design redundancy and regular testing.
Combination of technology and management : Intelligent monitoring makes up for the blind spots of manual inspection.
Everyone involved : From designers to operators, the consequences of failure must be clear.

Failure prevention tips :

"Strong materials, large rounded corners, frequent inspections, no overloading"
"Cracks don't last overnight, rust should be removed promptly"

By systematically analyzing failure modes and implementing strict preventive measures, the safety of hooks can be improved by more than 50%!

1. Common failure modes and cause analysis

1. Plastic deformation (permanent bending)

Phenomenon : The hook body or hook neck undergoes irreversible bending.
reason :
- Overload : Exceeding the rated load (such as more than 1.5 times the static load).
- Material defect : Inadequate yield strength due to improper heat treatment.
- Shock load : sudden acceleration/stop causes a sudden increase in dynamic stress.

2. Fatigue fracture

Phenomenon : Cracks extend from high stress areas (such as the base of the hook neck) to fracture.
reason :
- Cyclic loading : Frequent lifting leads to cumulative damage (see Miner's law).
- Stress concentration : insufficient design fillet or surface processing defects.
- Corrosive environment : accelerates crack initiation (such as marine salt spray).

3. Brittle fracture

Phenomenon : Sudden fracture without plastic deformation, and the cross section is granular.
reason :
- Low temperature operation : insufficient material toughness (e.g. impact energy < 27J at -20°C).
- Hydrogen embrittlement : Insufficient dehydrogenation after electroplating or pickling.

4. Wear and corrosion

Phenomenon :
- Hook wear : The friction of the sling causes the size to exceed the limit (>10% of the original size).
- Rust penetration : localized corrosion in chemical/marine environments.
reason :
- Insufficient lubrication : Dry friction of rotating parts.
- Failure of protective layer : paint peeling or plating damage.

5. Thread failure (detachable hook)

Phenomenon : Thread slippage, tooth collapse or loose connection.
reason :
- Not tightened according to torque : insufficient or excessive preload.
- Foreign matter intrusion : Dust/rust residue increases wear.

2. Preventive measures

1. Prevention during the design phase

Failure Mode	Design strategies
Plastic deformation	Safety factor ≥ 4 (GB/T 10051), FEA verifies stress distribution under extreme load.
fatigue fracture	Optimize the hook neck transition radius (R≥10mm) and use shot peening to increase the surface compressive stress.
Brittle fracture	Use low-temperature toughness materials (such as 34CrNiMo6) and prohibit electroplating.
Wear/Corrosion	The hook mouth is welded with a wear-resistant layer (such as Hardox 500), and 316 stainless steel is used for marine environment.
Thread failure	Use fine thread + anti-loosening nut (such as Nord-Lock washer).

2. Manufacturing and process control

Material inspection :
- Chemical composition analysis (spectrometer) + mechanical properties test (tensile, impact).
Heat treatment monitoring :
- After the quenching and tempering process (quenching + tempering), the hardness is controlled at HB 200~300.
Non-destructive testing (NDT) :
- 100% magnetic particle testing (MT) to detect surface cracks, and ultrasonic testing (UT) in critical areas.

3. Usage and maintenance measures

Failure Mode	Maintenance measures
Overload deformation	Install a torque limiter to automatically cut off the lifting power supply when overloaded.
Fatigue crack	MT inspection is carried out every 6 months and any cracks found will be scrapped immediately.
Corrosion and wear	Apply anti-rust grease (such as Castrol Rustilo) every month and use plastic sheath in chemical environment.
Loose threads	Check the torque regularly (e.g. M36 bolts require 1200 N·m) and use thread lockers.

4. Personnel training and monitoring

Operation Specifications :
- Oblique pulling and emergency stopping are prohibited, and the sling angle is ≤60°.
Intelligent monitoring :
- Strain sensors are installed to monitor loads in real time, and vibration sensors are used to warn of bearing failures.

III. Typical Cases and Lessons

Case 1: Fatigue fracture accident

Background : A crane hook at a port broke after 5 years of use, causing a container to fall.
Reason : The root of the hook neck was not shot peened and the fatigue crack expanded to a critical size.
Improvement : Make it mandatory to replace the hook every 2 years and add TOFD inspection.

Case 2: Thread slippage causes thread shedding

Background : The hook thread in the metallurgical workshop failed and the ladle tilted.
Cause : The lock nut was not used and the high temperature caused the grease to carbonize.
Improvement : Use high temperature resistant thread locking agent (such as Loctite 272).

4. Failure Analysis Process

On-site protection : Take photos to record the fracture morphology and damaged areas.
Laboratory testing :
- Fracture analysis : SEM scanning electron microscope is used to observe the crack source (such as fatigue striations).
- Metallographic examination : Check for heat treatment defects (such as decarburization layer).
Root cause reporting : Propose design/maintenance improvement plans.

V. Conclusion

Key principles :

Prevention is better than cure : Reduce risk through design redundancy and regular testing.
Combination of technology and management : Intelligent monitoring makes up for the blind spots of manual inspection.
Everyone involved : From designers to operators, the consequences of failure must be clear.

Failure prevention tips :

"Strong materials, large rounded corners, frequent inspections, no overloading"
"Cracks don't last overnight, rust should be removed promptly"

By systematically analyzing failure modes and implementing strict preventive measures, the safety of hooks can be improved by more than 50%!

1. Common failure modes and cause analysis

1. Plastic deformation (permanent bending)

Phenomenon : The hook body or hook neck undergoes irreversible bending.
reason :
- Overload : Exceeding the rated load (such as more than 1.5 times the static load).
- Material defect : Inadequate yield strength due to improper heat treatment.
- Shock load : sudden acceleration/stop causes a sudden increase in dynamic stress.

2. Fatigue fracture

Phenomenon : Cracks extend from high stress areas (such as the base of the hook neck) to fracture.
reason :
- Cyclic loading : Frequent lifting leads to cumulative damage (see Miner's law).
- Stress concentration : insufficient design fillet or surface processing defects.
- Corrosive environment : accelerates crack initiation (such as marine salt spray).

3. Brittle fracture

Phenomenon : Sudden fracture without plastic deformation, and the cross section is granular.
reason :
- Low temperature operation : insufficient material toughness (e.g. impact energy < 27J at -20°C).
- Hydrogen embrittlement : Insufficient dehydrogenation after electroplating or pickling.

4. Wear and corrosion

Phenomenon :
- Hook wear : The friction of the sling causes the size to exceed the limit (>10% of the original size).
- Rust penetration : localized corrosion in chemical/marine environments.
reason :
- Insufficient lubrication : Dry friction of rotating parts.
- Failure of protective layer : paint peeling or plating damage.

5. Thread failure (detachable hook)

Phenomenon : Thread slippage, tooth collapse or loose connection.
reason :
- Not tightened according to torque : insufficient or excessive preload.
- Foreign matter intrusion : Dust/rust residue increases wear.

2. Preventive measures

1. Prevention during the design phase

Failure Mode	Design strategies
Plastic deformation	Safety factor ≥ 4 (GB/T 10051), FEA verifies stress distribution under extreme load.
fatigue fracture	Optimize the hook neck transition radius (R≥10mm) and use shot peening to increase the surface compressive stress.
Brittle fracture	Use low-temperature toughness materials (such as 34CrNiMo6) and prohibit electroplating.
Wear/Corrosion	The hook mouth is welded with a wear-resistant layer (such as Hardox 500), and 316 stainless steel is used for marine environment.
Thread failure	Use fine thread + anti-loosening nut (such as Nord-Lock washer).

2. Manufacturing and process control

Material inspection :
- Chemical composition analysis (spectrometer) + mechanical properties test (tensile, impact).
Heat treatment monitoring :
- After the quenching and tempering process (quenching + tempering), the hardness is controlled at HB 200~300.
Non-destructive testing (NDT) :
- 100% magnetic particle testing (MT) to detect surface cracks, and ultrasonic testing (UT) in critical areas.

3. Usage and maintenance measures

Failure Mode	Maintenance measures
Overload deformation	Install a torque limiter to automatically cut off the lifting power supply when overloaded.
Fatigue crack	MT inspection is carried out every 6 months and any cracks found will be scrapped immediately.
Corrosion and wear	Apply anti-rust grease (such as Castrol Rustilo) every month and use plastic sheath in chemical environment.
Loose threads	Check the torque regularly (e.g. M36 bolts require 1200 N·m) and use thread lockers.

4. Personnel training and monitoring

Operation Specifications :
- Oblique pulling and emergency stopping are prohibited, and the sling angle is ≤60°.
Intelligent monitoring :
- Strain sensors are installed to monitor loads in real time, and vibration sensors are used to warn of bearing failures.

III. Typical Cases and Lessons

Case 1: Fatigue fracture accident

Background : A crane hook at a port broke after 5 years of use, causing a container to fall.
Reason : The root of the hook neck was not shot peened and the fatigue crack expanded to a critical size.
Improvement : Make it mandatory to replace the hook every 2 years and add TOFD inspection.

Case 2: Thread slippage causes thread shedding

Background : The hook thread in the metallurgical workshop failed and the ladle tilted.
Cause : The lock nut was not used and the high temperature caused the grease to carbonize.
Improvement : Use high temperature resistant thread locking agent (such as Loctite 272).

4. Failure Analysis Process

On-site protection : Take photos to record the fracture morphology and damaged areas.
Laboratory testing :
- Fracture analysis : SEM scanning electron microscope is used to observe the crack source (such as fatigue striations).
- Metallographic examination : Check for heat treatment defects (such as decarburization layer).
Root cause reporting : Propose design/maintenance improvement plans.

V. Conclusion

Key principles :

Prevention is better than cure : Reduce risk through design redundancy and regular testing.
Combination of technology and management : Intelligent monitoring makes up for the blind spots of manual inspection.
Everyone involved : From designers to operators, the consequences of failure must be clear.

Failure prevention tips :

"Strong materials, large rounded corners, frequent inspections, no overloading"
"Cracks don't last overnight, rust should be removed promptly"

By systematically analyzing failure modes and implementing strict preventive measures, the safety of hooks can be improved by more than 50%!

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