Offshore cranes must cope with both temperature fluctuations and salt spray corrosion. Temperature directly affects material properties, and material selection must be matched to the temperature range to avoid structural fractures, component failures, and other issues. The core logic and adaptation solutions are as follows:
1. Core Impact: The Dual Effects of Temperature and Marine Corrosion
Low temperature: Material toughness decreases (easily brittle), lubricating oil becomes thicker, salt spray icing accelerates coating damage, and the structure is easily exposed to salt spray environment;
High temperature: material softening (strength reduction), thermal fatigue, high temperature and high humidity exacerbate electrochemical corrosion;
Alternating temperature difference: thermal expansion and contraction generate stress, causing welds/coatings to crack and salt spray to penetrate through the gaps;
Room temperature: Mechanical properties are stable, but special attention should be paid to resistance to long-term salt spray.
2. Temperature range: material selection suggestions for key components
1. Low temperature (≤0℃, such as the Arctic and high-latitude sea areas)
The load-bearing structure (jib, base) of the offshore crane: select Q355ND (anti-brittleness at -40℃), 09MnNiD (applicable at -60℃), and match with marine anti-corrosion coating; ordinary Q235 and single-coated steel are prohibited.
Transmission parts (gears, bearings) of deck cranes: gears are made of 20CrMnTi (carburized for wear resistance), and bearings are made of GCr15SiMn (good low-temperature toughness); untempered 45 steel and ordinary GCr15 are prohibited.
Seals/rubber parts: EPDM (good elasticity at -50℃) is used for seals, and modified PVC is used for cable sheaths; ordinary nitrile rubber and unmodified PVC are prohibited.
2. High temperature (≥35°C, such as tropical oil fields and equatorial waters)
Marine crane load-bearing structure: Use Q355R (stable strength at 300℃), 15CrMo (resistant to high temperature oxidation), coated with fluorocarbon/composite anti-corrosion layer; Q235 and acrylic coating are prohibited.
Transmission/hydraulic parts of offshore cranes: 38CrMoAlA (nitrided for creep resistance) is used for hydraulic pumps, and synthetic high-temperature hydraulic oil is selected; mineral lubricants and non-sealed components are prohibited.
Ship crane electrical parts: Motors should use H-class insulation (resistant to 180°C) and cables should use silicone rubber insulation; B-class insulation motors and PVC cables are prohibited.
3. Normal temperature (10℃-30℃, such as temperate coastal areas)
Offshore crane load-bearing structure: Q355B (with composite anti-corrosion coating), 316L stainless steel for corrosion-prone areas;
Transmission parts of marine cranes: shafts are made of 40Cr (quenched and tempered chrome-plated), and bearings are sealed GCr15;
Sealing/Electrical of boat cranes: Nitrile rubber for sealing and XLPE insulation for cables.
4. Alternating temperature difference (day and night difference ≥ 20℃)
The structure is made of Q355ND (stable thermal expansion) and Invar alloy (precision parts);
The welds are treated with low-hydrogen electrodes and stress-relieving treatment, and the coating is elastic polyurethane.
3. Key Verification: Two Required Tests
Low temperature impact test: ensure that the impact energy meets the standard at -40℃ (or target low temperature) to prevent cold brittleness;
Salt spray test: neutral salt spray for more than 1000 hours, no damage to the coating and little pitting of the substrate.
4. Summary: Material Selection Process
Clearly define the operating temperature range + salt spray concentration;
Select materials based on the component requirements of deck cranes (e.g., structural brittleness and transmission wear resistance);
Priority is given to materials with marine classification society certification (ABS, CCS, DNV, LR, etc.);
Low temperature shock and salt spray testing are carried out before leaving the factory.
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