Design Of Corrosion Resistant Surfacing Layer Of Pipe Inner Wall And Research On Its Corrosion Resistance

The inner wall of the water pipeline is mostly coated with organic or inorganic coatings to reduce corrosion.However,when the pipeline is welded,the coating in the near seam area is easily damaged by the high temperature of the welding,which accelerates the corrosion of the welded joint region.Therefore,this paper proposes a method to weld the corrosion resistant alloy layer at the pipe end to solve this problem.Because the corrosion of tap water is weak,in order to improve the welding production efficiency and reduce the production cost,this paper designs a low alloy corrosion resistant surfacing material for the service environent.Based on the existing two low alloy wire components,different alloying elements are added to obtain the test materials.Electrochemical test,rotating coupon test and SEM,EDS,XRD,EBSD and other analytical techniques were used to systematically study the corrosion electrochemical behavior of rare earth elements,nickel and chromium in low-alloy materials in the tap water environment.The structure and the influence of the corrosion mechanism.According to the research results of corrosion behavior of materials,the optimal scheme is proposed,and the surfacing process optimization is further carried out for the preferred materials,and the corrosion resistance of the surfacing layer is further studied.The conclusions are as follows:(1)The addition of Ce can accelerates the corrosion rate of the material to a stable state,and promotes the formation of protective corrosion products at the beginning of corrosion,thereby reducing the corrosion rate of the material.(2)As the nickel content increases,the corrosion rate of the material gradually decreases.When the nickel content reached 5%,the corrosion resistance of the material was significantly improved,and the corrosion rate at 720 h was only 27%of 1%Ni Ce,34%of 2%Ni Ce,and37%of 3%Ni Ce.Cr can promote the conversion of?-Fe OOH to?-Fe OOH in the early stage of corrosion,thereby improving the protection of the corrosion product film and reducing the corrosion rate of the material.Therefore,the chromium-containing material exhibits better corrosion resistance.(3)The mechanism of nickel improving the corrosion resistance of the material is that nickel can promote the conversion of Fe₃O₄ to Ni Fe₂O₄,and the higher the nickel content,the stronger the promotion effect,the higher the compactness and stability of the corrosion product film;the increase of nickel content,the cementite The content is gradually reduced,thereby reducing the location of corrosion initiation.(4)Compared with nickel,chromium-containing materials exhibit better corrosion resistance.The mechanism is that chromium can significantly accelerate the conversion of?-Fe OOH to?-Fe OOH at the initial stage of corrosion,thereby improving the protection of the corrosion product film.(5)The optimal process parameters were obtained by quadratic regression orthogonal rotation combination design and analysis of regression equations:X₁(Welding Current is212A),X₂(Hot Wire Current is 49A),and X₃(Wire Feeding Speed is 4.0m·min^-1),X₄(Welding Speed is 2.2mm·s^-1),and the overlap ratio is 50%.(6)After surfacing,the microstructure of 5%Ni RE is mainly composed of lath martensite,and the distribution is more uniform,so that the self-corrosion current density is reduced from30.4314?A·cm^-2 to 5.6698?A·cm^-2;3%Cr RE The self-corrosion current density is reduced from 22.8249?A·cm^-2 to 4.7296?A·cm^-2,which is the result of uniform microstructure,refinement and a significant decrease in the number of corroded microbatteries.