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crane hooks may bend, twist or partially deform during long-term use , but not all deformations can be repaired. Safety standards must be strictly followed to ensure that the structural strength is not affected after correction . The following are the correction methods and precautions for hook deformation:

1. The range of deformation allowed for correction

Note : If the hook is cracked, severely rusted or the material is deteriorated , it must be scrapped directly and cannot be corrected!

2. Common correction methods

1. Cold correction (suitable for small deformation)

Applicable scenarios : slight bending or local deformation (such as slight deflection of the hook tip).
Tools : hydraulic jack, special correction fixture, copper hammer.
Steps :

1. Secure the hook : Use a clamp or vise to stabilize the hook to prevent it from slipping.

2. Apply pressure slowly : Use a jack or press to apply force in the opposite direction to the deformed part.

3. Check and restore : Use a caliper to measure and ensure that it is restored to its original size (error <3%).

4. Annealing (optional): If the material is hardened, low temperature annealing (200~300℃) can be used to eliminate stress.

Risk : Excessive cold straightening may cause micro cracks, and magnetic particle testing (MT) is required after straightening .

2. Thermal correction (use with caution)

Applicable scenarios : large deformation (such as hook bending), but must be performed by professionals.
Tools : oxy-acetylene flame, thermometer, hydraulic press.
Steps :

1. Local heating : Use flame to heat the deformed area to 600~700℃ (dark red) , avoid overheating (＞800℃ will cause material degradation).

2. Pressurize slowly : Use a press to correct while hot, avoiding shock loads.

3. Natural cooling : water quenching is prohibited to prevent embrittlement.

4. Testing and heat treatment :

   • Annealing (stress relief) is required after correction .

   • Perform hardness test and MT/UT inspection to confirm there are no cracks.

Risk : Improper heating will change the material properties and must strictly follow ASME B30.10 or ISO 2415 standards.

3. Machining repair

Applicable scenarios : thread damage or pin hole deformation.
Method :

• Reaming repair : enlarge the pin hole and install a new pin (the wall thickness must be ≥ 90% of the original size).

• Thread repair : Use a tap to repair or replace the nut (welding to repair threads is prohibited).

3. Corrected testing requirements

1. Visual inspection : Confirm that there are no visible cracks or burn marks.

2. Non-destructive testing (NDT) :

   • Magnetic Particle Testing (MT) : Checks for surface cracks.

   • Ultrasonic Testing (UT) : Detects internal defects.

3. Load test :

   • No permanent deformation when static load of 150% WLL is applied (1 minute).

IV. Circumstances in which correction is prohibited

1. Cracks (of any length, even after correction).

2. Hook deformation ≥ 10% (ASME B30.10 mandatory scrapping standard).

3. High temperature causes material properties to deteriorate (e.g. hardness < HB 250).

4. Deformation of key stress-bearing areas (such as the inside of the hook throat).

5. Comparison of International Standards

in conclusion

1. Prefer replacement over correction : Hooks are cheap and the cost of correction may exceed the cost of a new purchase.

2. Only professionals can do this : thermal correction must be performed by a certified welder or heat treatment engineer.

3. Safety first : If the safety after correction cannot be 100% guaranteed, it must be scrapped!

Recommendation : Establish a correction record file , including correction methods, test data and responsible persons, for traceability.