Core Technical Indicators and Surface Treatment Methods for Marine Anchor Chains and Offshore Mooring Chains-Part 2

2.3 Core Mechanical Performance Indicators

2.4 Geometric Dimensional Accuracy Indicators

2.5 Welding and Heat Treatment Performance Indicators

1. Welding Performance
   • Both adopt flash butt welding process. The mechanical properties of the welded joint must not be lower than that of the base metal. The impact energy of the welded joint of marine anchor chains shall not be less than 80% of that of the base metal, and the welded joint performance of offshore mooring chains must fully match the base metal.
   • 100% non-destructive testing of welds is required. Offshore mooring chains must pass both UT (Ultrasonic Testing) and MT (Magnetic Particle Testing). Defects such as cracks, incomplete penetration and slag inclusion exceeding the standard are not allowed. The defect grinding depth shall not exceed 5% of the chain diameter, and weld repair is strictly prohibited.
   
   
2. Heat Treatment Performance
   • Integral quenching and high-temperature tempering (thermal refining) must be adopted to obtain a uniform tempered sorbite structure with a grain size of Grade 5~8, ensuring the balance between strength and toughness of the chain.
   • The hardness fluctuation after heat treatment of the same batch of products shall be ≤30HB. Offshore mooring chains require hardness testing link by link to ensure performance uniformity.
   
   

2.6 Fatigue and Corrosion Resistance Indicators (Core Assessment Items for Offshore Mooring Chains)

1. Fatigue Performance
   • Marine anchor chains: For temporary mooring conditions, the conventional requirement is no fracture after ≥2×10^4 cycles under pulsating load. Studless chains require additional assessment of fatigue performance under torsional load.
   • Offshore mooring chains: For long-term alternating load conditions, corrosion fatigue test is mandatory. No fracture shall occur after ≥2×10^6 cycles at a stress ratio R=0.1. The dynamic fatigue analysis of the mooring system must be passed to meet the fatigue life requirement of more than 20 years of service.
   
   
2. Corrosion Resistance
   • Marine anchor chains: Must pass 1000h neutral salt spray test without red rust and coating peeling, meeting the anti-corrosion requirements of marine atmosphere and temporary immersion.
   • Offshore mooring chains: Must pass NACE TM0177 Sulfide Stress Corrosion Cracking (SSCC) Test and Hydrogen-Induced Cracking (HIC) Test. For acidic oil and gas field conditions, additional acidic environment corrosion test is required. The uniform corrosion rate under long-term seawater immersion shall be ≤0.1mm/year.