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Repair solution for excessive wear of crane hook

2025-07-29 06:01:36

The repair of excessively worn crane hooks must strictly follow safety standards to ensure that the performance after repair is not lower than the original design requirements. The following are graded repair plans and criteria for determining whether a crane cannot be repaired and scrapped:

1. Determination of Repairable Conditions

  1. Allowable repair scope :

    • Hook mouth uniform wear ≤ 10% original size (GB/T 10051.1)

    • No cracks or plastic deformation (tested by MT/UT)

    • Thread wear ≤ 6H tolerance (GB/T 197)

  2. Mandatory scrapping standards :

    • Hook mouth wear > 12mm (based on a 50mm standard hook mouth)

    • Cracks in any area

    • Torsion deformation＞5°

2. Graded Restoration Plan

1. Repair of minor wear (wear ≤ 5%)

Process selection :

  • Laser cladding repair :

    • Material: Cobalt-based alloy powder (Stellite 6)

    • Parameters: Power 2-3kW, powder feeding rate 15g/min

    • Advantages: Heat affected zone <0.5mm, hardness restored to HRC40-45

  • Cold weld repair :

    • Applicable: Surface wear in non-load-bearing areas

    • Material: ER309L stainless steel welding wire

    • Layer thickness control: single layer ≤ 1.5mm

Acceptance criteria :

  • Hardness deviation ≤±5HRC original value

  • Dimensional tolerance restored to IT8 level

2. Moderate wear repair (5%-10% wear)

Composite repair process :

  1. Substrate pretreatment :

    • Sand blasting (Sa2.5 level)

    • Preheat to 150-200℃ (34CrMo material)

  2. Plasma cladding :

    • Powder: Fe-Cr-B-Si (hardness HRC55-60)

    • Dilution rate control <15%

  3. finishing :

    • CNC turning recovery profile

    • Rolling strengthening (surface roughness Ra ≤ 3.2μm)

Process Validation :

  • Penetrant testing (PT) without defects

  • 1.25 times static load test for 10 minutes

3. Special repair technology

  1. Nano brush plating repair :

    • Applicable: Bearing fitting surface wear

    • Plating solution: Ni-Co-SiC nanocomposite coating

    • Thickness: 0.05-0.2mm

  2. 3D printing repair :

    • Equipment: Laser Directed Energy Deposition (DED)

    • Material: 34CrMo powder of the same quality as the matrix

    • Subsequent quenching and tempering heat treatment is required

4. Post-repair inspection specifications

Test items Method Standards Qualified indicators
Dimensional accuracy GB/T 3177 Hook roundness ≤0.1mm
Surface hardness GB/T 230.1 Fluctuation range ≤15% of substrate hardness
Residual stress X-ray diffraction Compressive stress＞-200MPa
Fatigue performance GB/T 3075 Number of cycles ≥ 80% of original design

5. Economic Comparison

Repair method Cost (yuan/kg) Lifetime recovery rate
Laser Cladding 120-180 95%-105%
Plasma cladding 80-120 85%-95%
Replace the hook 200-300 100%

6. Notes

  1. Repair is prohibited in the following cases :

    • There are micro cracks in the load-bearing area (confirmed by SEM testing)

    • Wear on key transition fillets

    • Hooks that have been repaired more than 3 times

  2. Restoration qualification requirements :

    • Special equipment welding qualification (TSG Z6002) is required

    • Process assessment complies with NB/T 47014

Conclusion and suggestions :

  • When the wear amount is greater than 8%, replace the hook with a new one first

  • After repair, the hook needs to be downgraded (e.g. a 50t hook can be used as a 40t hook after repair)

  • Establish repair files (including process parameters, test data)

Note: Before all repair work, finite element analysis must be performed to verify the stress distribution in the repair area to ensure that the maximum Von Mises stress does not exceed 35% of the material yield strength.

The repair of excessively worn crane hooks must strictly follow safety standards to ensure that the performance after repair is not lower than the original design requirements. The following are graded repair plans and criteria for determining whether a crane cannot be repaired and scrapped:

1. Determination of Repairable Conditions

  1. Allowable repair scope :

    • Hook mouth uniform wear ≤ 10% original size (GB/T 10051.1)

    • No cracks or plastic deformation (tested by MT/UT)

    • Thread wear ≤ 6H tolerance (GB/T 197)

  2. Mandatory scrapping standards :

    • Hook mouth wear > 12mm (based on a 50mm standard hook mouth)

    • Cracks in any area

    • Torsion deformation＞5°

2. Graded Restoration Plan

1. Repair of minor wear (wear ≤ 5%)

Process selection :

  • Laser cladding repair :

    • Material: Cobalt-based alloy powder (Stellite 6)

    • Parameters: Power 2-3kW, powder feeding rate 15g/min

    • Advantages: Heat affected zone <0.5mm, hardness restored to HRC40-45

  • Cold weld repair :

    • Applicable: Surface wear in non-load-bearing areas

    • Material: ER309L stainless steel welding wire

    • Layer thickness control: single layer ≤ 1.5mm

Acceptance criteria :

  • Hardness deviation ≤±5HRC original value

  • Dimensional tolerance restored to IT8 level

2. Moderate wear repair (5%-10% wear)

Composite repair process :

  1. Substrate pretreatment :

    • Sand blasting (Sa2.5 level)

    • Preheat to 150-200℃ (34CrMo material)

  2. Plasma cladding :

    • Powder: Fe-Cr-B-Si (hardness HRC55-60)

    • Dilution rate control <15%

  3. finishing :

    • CNC turning recovery profile

    • Rolling strengthening (surface roughness Ra ≤ 3.2μm)

Process Validation :

  • Penetrant testing (PT) without defects

  • 1.25 times static load test for 10 minutes

3. Special repair technology

  1. Nano brush plating repair :

    • Applicable: Bearing fitting surface wear

    • Plating solution: Ni-Co-SiC nanocomposite coating

    • Thickness: 0.05-0.2mm

  2. 3D printing repair :

    • Equipment: Laser Directed Energy Deposition (DED)

    • Material: 34CrMo powder of the same quality as the matrix

    • Subsequent quenching and tempering heat treatment is required

4. Post-repair inspection specifications

Test items Method Standards Qualified indicators
Dimensional accuracy GB/T 3177 Hook roundness ≤0.1mm
Surface hardness GB/T 230.1 Fluctuation range ≤15% of substrate hardness
Residual stress X-ray diffraction Compressive stress＞-200MPa
Fatigue performance GB/T 3075 Number of cycles ≥ 80% of original design

5. Economic Comparison

Repair method Cost (yuan/kg) Lifetime recovery rate
Laser Cladding 120-180 95%-105%
Plasma cladding 80-120 85%-95%
Replace the hook 200-300 100%

6. Notes

  1. Repair is prohibited in the following cases :

    • There are micro cracks in the load-bearing area (confirmed by SEM testing)

    • Wear on key transition fillets

    • Hooks that have been repaired more than 3 times

  2. Restoration qualification requirements :

    • Special equipment welding qualification (TSG Z6002) is required

    • Process assessment complies with NB/T 47014

Conclusion and suggestions :

  • When the wear amount is greater than 8%, replace the hook with a new one first

  • After repair, the hook needs to be downgraded (e.g. a 50t hook can be used as a 40t hook after repair)

  • Establish repair files (including process parameters, test data)

Note: Before all repair work, finite element analysis must be performed to verify the stress distribution in the repair area to ensure that the maximum Von Mises stress does not exceed 35% of the material yield strength.

The repair of excessively worn crane hooks must strictly follow safety standards to ensure that the performance after repair is not lower than the original design requirements. The following are graded repair plans and criteria for determining whether a crane cannot be repaired and scrapped:

1. Determination of Repairable Conditions

  1. Allowable repair scope :

    • Hook mouth uniform wear ≤ 10% original size (GB/T 10051.1)

    • No cracks or plastic deformation (tested by MT/UT)

    • Thread wear ≤ 6H tolerance (GB/T 197)

  2. Mandatory scrapping standards :

    • Hook mouth wear > 12mm (based on a 50mm standard hook mouth)

    • Cracks in any area

    • Torsion deformation＞5°

2. Graded Restoration Plan

1. Repair of minor wear (wear ≤ 5%)

Process selection :

  • Laser cladding repair :

    • Material: Cobalt-based alloy powder (Stellite 6)

    • Parameters: Power 2-3kW, powder feeding rate 15g/min

    • Advantages: Heat affected zone <0.5mm, hardness restored to HRC40-45

  • Cold weld repair :

    • Applicable: Surface wear in non-load-bearing areas

    • Material: ER309L stainless steel welding wire

    • Layer thickness control: single layer ≤ 1.5mm

Acceptance criteria :

  • Hardness deviation ≤±5HRC original value

  • Dimensional tolerance restored to IT8 level

2. Moderate wear repair (5%-10% wear)

Composite repair process :

  1. Substrate pretreatment :

    • Sand blasting (Sa2.5 level)

    • Preheat to 150-200℃ (34CrMo material)

  2. Plasma cladding :

    • Powder: Fe-Cr-B-Si (hardness HRC55-60)

    • Dilution rate control <15%

  3. finishing :

    • CNC turning recovery profile

    • Rolling strengthening (surface roughness Ra ≤ 3.2μm)

Process Validation :

  • Penetrant testing (PT) without defects

  • 1.25 times static load test for 10 minutes

3. Special repair technology

  1. Nano brush plating repair :

    • Applicable: Bearing fitting surface wear

    • Plating solution: Ni-Co-SiC nanocomposite coating

    • Thickness: 0.05-0.2mm

  2. 3D printing repair :

    • Equipment: Laser Directed Energy Deposition (DED)

    • Material: 34CrMo powder of the same quality as the matrix

    • Subsequent quenching and tempering heat treatment is required

4. Post-repair inspection specifications

Test items Method Standards Qualified indicators
Dimensional accuracy GB/T 3177 Hook roundness ≤0.1mm
Surface hardness GB/T 230.1 Fluctuation range ≤15% of substrate hardness
Residual stress X-ray diffraction Compressive stress＞-200MPa
Fatigue performance GB/T 3075 Number of cycles ≥ 80% of original design

5. Economic Comparison

Repair method Cost (yuan/kg) Lifetime recovery rate
Laser Cladding 120-180 95%-105%
Plasma cladding 80-120 85%-95%
Replace the hook 200-300 100%

6. Notes

  1. Repair is prohibited in the following cases :

    • There are micro cracks in the load-bearing area (confirmed by SEM testing)

    • Wear on key transition fillets

    • Hooks that have been repaired more than 3 times

  2. Restoration qualification requirements :

    • Special equipment welding qualification (TSG Z6002) is required

    • Process assessment complies with NB/T 47014

Conclusion and suggestions :

  • When the wear amount is greater than 8%, replace the hook with a new one first

  • After repair, the hook needs to be downgraded (e.g. a 50t hook can be used as a 40t hook after repair)

  • Establish repair files (including process parameters, test data)

Note: Before all repair work, finite element analysis must be performed to verify the stress distribution in the repair area to ensure that the maximum Von Mises stress does not exceed 35% of the material yield strength.

Pre: Lessons and improvements from crane hook overload accidents
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