News

1. Safety Factor

The safety factor is the ratio of the hook's load capacity to the actual working load, and is used to ensure safety margin under various working conditions.

1. Safety factor requirements of international standards

2. Safety factor calculation

• Static load safety factor  = minimum breaking load (MBL) / rated working load (WLL)
  (Example: MBL=50 tons, WLL=10 tons → safety factor = 5)

• Dynamic load safety factor  = MBL / (WLL × dynamic factor)
  (The dynamic factor is usually 1.25~1.5, depending on the working conditions)

2. Failure Mode and Cause Analysis

Hook failures are usually caused by material defects, overloading, fatigue or corrosion and can be divided into the following categories:

1. Fracture failure (most dangerous)

• reason :

  • Internal defects of materials (pores, inclusions)

  • Overload or shock load (such as emergency braking)

  • Fatigue crack growth (long term cyclic loading)

• Typical features :

  • Brittle fracture: the cross section is smooth and there is no plastic deformation (common in low temperature or high hardness materials)

  • Ductile fracture: The cross section is cup-conical with necking

2. Plastic deformation

• reason :

  • Short-term overload (exceeding yield strength)

  • Insufficient design safety factor

• Performance :

  • The hook is permanently open (if it exceeds 10% of the original size, it must be scrapped)

3. Fatigue failure

• reason :

  • Long-term exposure to alternating loads (such as frequent loading and unloading at ports)

  • Stress concentration (thread root, inside of hook throat)

• Development process :
  crack initiation → slow expansion → sudden fracture

• Precautions :

  • Regular NDT testing (magnetic particle/ultrasonic)

  • Optimize design (reduce stress concentration)

4. Wear and corrosion

• Wear :

  • The friction between the hook tip and the wire rope causes the cross-section loss (≥10% is scrapped)

• corrosion :

  • Wet/chemical environments induce rust and reduce load-bearing capacity

3. Failure Cases and Lessons

IV. Preventive measures

1. Design Phase

   • Optimizing stress distribution using finite element analysis (FEA)

   • Choose high toughness materials (such as 34CrMo4, impact energy ≥ 40J)

2. Manufacturing stage

   • Heat treatment after forging (quenching + tempering)

   • 100% Magnetic Particle Testing (MT)

3. Use phase

   • Overloading is strictly prohibited, and dynamic load impact is controlled

   • Daily Inspection + Annual NDT

4. Obsolescence Management

   • Strictly implement the scrapping standards of 10% deformation, 10% cracks and 10% wear

V. Analytical Tools and Techniques

• Fracture mechanics analysis : Calculation of critical crack size (based on stress intensity factor KIC)

• Metallographic analysis : determine the origin of failure (such as inclusions, intergranular corrosion)

• Scanning electron microscope (SEM) : observe the fracture morphology (dimples, cleavage, etc.)

in conclusion

1. The safety factor is the bottom line of hook safety and needs to be adjusted dynamically according to working conditions (such as dynamic load, corrosive environment).

2. Most failures are caused by "negligence in testing" or "illegal operation" , and the implementation of the system needs to be strengthened.

3. Preventive maintenance is more economical than post-event remediation , and intelligent monitoring (such as strain sensors + AI early warning) is recommended.

Note : For critical occasions (such as nuclear power and aerospace), the safety factor can be increased to ≥8 , and a redundant design (double hook backup) can be adopted.