Application Research Of Hot-wire TIG Welding In Oil And Gas Transmission Bimetal Composite Pipe

In order to ensure the safety of the extraction and transportation of acidic oil and natural gas,bimetal composite pipes have been developed.However,in the welding process of bimetal composite pipes,defects such as air holes and slag inclusions may occur,which seriously affect the mechanical properties and corrosion resistance of the welded joints.Hot-wire TIG welding is an efficient,high-quality welding method that can effectively solve the problems encountered in the welding process of composite pipes.In this thesis,automatic and semi-automatic hot-wire TIG welding methods were used to weld the L360QS/N08825bimetal composite pipe,and the microstructure,mechanical properties and corrosion resistance of the welded joints under the two process conditions were studied.The main conclusions are as follows:（1）The welded joints of automatic and semi-automatic hot-wire TIG welded joints of bimetal composite pipes all contain a large amount of austenite（A）and a small amount of ferrite（F）,and which will provide good corrosion resistance.（2）The tensile strength performance,bending performance,and low temperature impact performance of automatic hot-wire TIG welded joints are better than semi-automatic ones.From the perspective of mechanical properties,it is recommended to use the automatic hot-wire TIG welding method.The average tensile strength of the welded joints can reach541MPa,and the impact energy of the heat affected zone（HAZ）can reach 264J.The bending test and hardness test meet the standard requirements..（3）Corrosion electrochemical experiments and immersion corrosion experiments show that the automatic and semi-automatic hot-wire TIG welded joints have good corrosion resistance.In different weld passes of multi-layer and multi-pass welding,the corrosion resistance of the cover layer is better than that of the filling,transition and root welding layers.In comparison,the corrosion resistance of automatic welded joints is even better.The corrosion current density of the capping layer is 1.38411×10^-6A/cm²;the corrosion rate in the simulated gas field aqueous solution at 90°C is only 0.00567mm/a.