The Research And Development Of H Section Steel Used In Offshore Platform

With the constant consumption of continental oil and gas resources, Marine has become a important field of oil and gas development in the world. Large offshore oil engineering building needs a lot of special steel plates and H sections. Due to the equipments and technological conditions limits in the domestic iron and steel enterprises, H sections used in offshore oil engineering platform are mostly imported from abroad. In this paper, two typical H sections used in offshore platform:SM490YB and D36 were successfully developed combing with the actual production process and relying on the existing equipment conditions in Laiwu Steel Corporation. The SM490YB and D36 has certified by DNV and ABS, and successively applied to Cnooc Tanggu, Huangdao, and Zhanjiang base etc. Laiwu Steel Corporation plays a very good leadership in the development of H section used in ocean engineering in the domestic, as well as creates good economic benefits for Laiwu Steel Corporation.The paper’s main research content:The research of microalloying technology, structure strengthening mechanism, and inclusion control technology for steel. The content of sulphur, phosphorus and inclusion control in steel, stabilize the continuous casting process, determine the reheating temperature, control the deformation quantity of each pass and accumulative deformation rate in the universal rolling mill, control finishing temperature, reduce the abnormal structure such as zonal structure and Widmannstaetten structure to improve low temperature lateral impact toughness of steel.Chief original work is as follows:(1) The production process of H section used in offshore platform was studied based on the production process in Laiwu Steel Corporation. The chemical composition and microalloying technology were designed, and inclusion control technology, beam blank quality control technology, control rolling technology, residual stress control technology was studied. Moreover, the influence of various technological parameters on the microstructures and performance was analyzed.(2) The smelting process and continuous casting process was made for SM490YB and D36. Low S and P smelting process was studied in order to reduce the content of P and S, with the content of S≤0.010%, P≤0.020%, meanwhile, wire-feeding technique was used for inclusion modification(3) The causes of the beam blank web crack formation for niobium (Nb) bearing steel were analyzed, and the original idea such as controlling the as-cast structure, the range of molten steel composition, inclusion, protecting slag and mould cooling intensity were proposed to improve the beam blank quality. The web cracks have been solved by reasonably controlling smelting process, the use of secondary cooling water distribution weak cooling technology, reducing the temperature of R angle and web, reasonably controlling the temperature of withdrawal and straightening.(4) The mechanism of mixed grain size for H section was analyzed and the influence rules of the composition segregation and the rolling process parameters on mixed grain size were studied. The mixed grain size have been solved by a series of measures such as narrow composition control, and finishing start temperature controlled 40℃ below recrystallization temperature and above Ar3 temperature.(5) The influence of alloying elements, reheat temperature and deformation system on the impact toughness was studied. The influence rules of non-recrystallization zone rolling and metallographic structure on the structure and performance were discussed in this paper. Meanwhile, hot rolling key technology such as niobium (Nb) bearing H section reducing eccentric and web and flange extending matching were developed.(6) The corrosion-resisting property for H section used in offshore oil platform was studied and analyzed by using cyclic accelerated corrosion test and electrochemical polarization test. The influence of the different metallurgical process conditions on the corrosion-resisting property for H section used in offshore oil platform was studied.(7) The temperature field distribution during rolling H section was simulated and the influence rules of the finishing temperature, phase transformation, environmental temperature on residual stress were given. A series of measures such as universal mill equipped with waterproof board, reducing the temperature difference between the web and the flange were put forward to reduce the residual stress during hot rolling and to ensure the stability of product structure and performance.(8) The production process theory system for H section used in offshore oil platform was studied and established. Moreover, a relatively complete Technology management system has formed. It can meet strict performance requirements with low-temperature impact endurance, good weldability and high strength in different environmental conditions.