1. The platform structure is huge and consumes a lot of steel. For example, a jacket-type fixed oil production platform with a water depth of 100m needs to consume 15,000t of steel. When the water depth is 140-150m, it needs to consume 40,000t of steel, and when the water depth is 300m, it consumes 60,000t of steel.
2. The size and thickness of the components are large. The thickness of the components is generally 15-75mm, the thickness of some local components can reach 100mm, and the thickness of the steel for the rack of the self-elevating platform can reach 125-150mm.
3. Most types of platform steel are plates and pipes. Since the pipe has the smallest shape resistance in seawater, the impact force of the waves is also the least, so the columns, legs, supports and other structures of the offshore platform are all made of pipes, and the large diameter pipes are rolled and welded with steel plates.
4. There are many types of steel used in platform steel. In order to ensure the strength and stability of large-scale structures, a large number of ordinary-strength steel and medium-strength steel are used, and the size of the components is increased to ensure sufficient rigidity; however, for high-stress areas bearing high loads, in order to reduce self-weight and improve strength.
5. The platform structure is complex, and there is a high stress in the thickness direction at some node connections. During welding these stresses may be higher than the yield strength of the material. If the plasticity of the material is not good enough in the thickness direction, it is possible to produce cold cracks in the thickness direction, that is, laminar tearing, so the platform construction needs to use anti-lamellar tearing steel ¾¾ Z direction steel.
6. The welding workload of the huge platform structure is very large. If the weldability of the steel is not good, not only a high preheating temperature is required, but also the quality is not easy to guarantee. Therefore, improving the weldability of steel is a crucial issue for platform steel. In order to improve the welding quality, while improving the welding process, all countries are studying new steel grades with good weldability without preheating and cracks in large thicknesses.
7. The platform has been corroded by seawater for a long time in the marine environment, and the thickness of the components is gradually lost. Coupled with the repeated impact of waves, storms, quicksand, etc., corrosion fatigue may also occur. Seawater corrosion reduces the service life of the platform, so in addition to taking various anti-corrosion measures, it is also hoped that the steel used has high seawater corrosion resistance.
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