The Research Of Weld Cladding Of Incoloy 825 On The X65 Pipe By Hot Wire P-TIG Welding

Currently,the exploitation of offshore oil and gas fields have entered the stage of rapid development,but due to the reasons such as corrosion in the process of exploitation,the failure accidents of the pipeline take place frequently,which lead to the obstruction of the transportation.So,it is necessary and urgent to develop a new type pipe that can both ensure the safety and reduce the production cost.The clad pipe is just the new pipe that resists to the corrosion in the high acidic environment.The clad pipe combines the excellent corrosion resistance of the corrosion resistant alloy with the excellent mechanical properties of he pipeline steel.Besides,it improve the level of security and the production cost is relatively low.In this paper,the hot wire P-TIG was used to clad Incoloy 825 on the surface of X 65 pipeline steel.The various forming defects during the welding process was investigated,based on which the welding parameters were determined.And the micro-structure and mechanical of Incoloy825 cladding was studied.Firstly,a serious of forming defects were discovered,such as undercut,the drop of the weld bead,the oxidation of the surface,the burning loss of the tungsten electrode tip,the tungsten electrode is stained with dirt,the directionality of the fillers is bad.The above phenomenon was analyzed and the reasons were found out which provide theoretical basis for the determination of the parameters.Secondly,due to ensure the stability of the welding process,the fillers should always insert in the molten pool,for that reason we research the matching relation between the hot wire current and the wire feed rate.Next,the welding current,welding speed and the wire feed rate are determined by the orthogonal test.After the welding parameters were fixed,the other influencing factors in the welding forming were qualitatively analyzed,including the slope angle of tungsten electrode,the shape of the tungsten electrode tip,the distance between adjacent welding bead,the position of wire feeding and so on.Based on the above parameters,an optimal welding forming was achieved and the average thickness of the cladding alloy is estimated.Finally,the micro-structural and mechanical characterizations of Incoloy 825 cladding were studied,and the rate of dilution was calculated.The results show that there are several discontinuous partially-mixed zones(PMZ)at the bottom of the cladding.The micro-structural of the cladding alloy is consist of the columnar dendrite and the isometric dendrite.The direction of the columnar dendrite is disorder,and the isometric dendrite is tiny,which presents the typical characteristics of solidified structure.The nondestructive test,bending test,pitting test and the electrochemical corrosion test of the cladding alloy all meet the requirements.From the side X65 to the Incoloy 825,the content of the element Fe quickly decreased and the other elements were increased.The highest hardness occurred on the base metal closed to the fusion line.In addition,the rate of dilution is less than 5 percent,which meets the requirement.