At present, the four international standards of offshore platform steel, namely En10225 and BS7191 (European Standard), API (American Standard) and Norsok (North Sea Standard), have clear stipulations on the mechanical properties, design and manufacture of offshore platform steel.


The yield strength of the main grades of high strength steel for offshore platforms in the world is 355,420,460,500,550,620,690 MPa. The low temperature performance requirements are at least - 40 degrees C, or even - 60 degrees C. The layer tear resistance Z is 35%, and the corrosion resistance is good.


Chemical Composition Requirements of Steel for Marine Engineering
The factors affecting the properties of steel include chemical composition, smelting and casting, rolling and heat treatment process, which are mainly composed of chemical composition. The content of sulfur and phosphorus directly affects the properties of steel plate in thickness direction. Sulphur is the most serious segregation element in continuous casting slab. Sulphur will cause steel to become hot and brittle, and cracks will appear in steel during high temperature forging. Many loosening and ventilation holes will occur during welding.


Phosphorus is a highly segregated element next to sulphur in continuous casting billet of steel, and the diffusion rate of phosphorus in iron solid solution is small, so the segregation of phosphorus is difficult to eliminate, which seriously affects the properties of steel. Phosphorus dissolves in ferrite as a solid solution. The solid solution is very brittle. The phosphorus-rich zone formed promotes the brittleness of steel and reduces the plasticity, toughness and weldability of steel. It is easy to cause cracks in steel during hot working, and cracks may occur during welding. Phosphorus is an element that reduces the surface tension of steel. With the increase of phosphorus content, the surface tension of molten steel decreases significantly, which reduces the crack resistance of steel.


Therefore, there are strict requirements for sulfur and phosphorus content in steel plates for offshore platforms, and sulfur content should be strictly controlled.


Performance Requirements of Marine Engineering Steel
Because offshore platforms are immersed in sea water all year round, they must endure all kinds of harsh sea conditions. Therefore, the technical index of offshore platform steel is very high. It not only has high atmospheric corrosion resistance and seawater corrosion resistance, but also needs good mechanical and processing properties. The performance requirements of steel for offshore platforms include:


(1) High strength and resistance to wind impact above water surface.
(2) It has good low-temperature impact performance.
(3) Good welding performance.
(4) Purity requirements of steel.
(5) Corrosion resistance requirements.