Pipeline transportation is the main component of today's comprehensive transportation system, together with railway, highway, water transportation, aviation, constitute the basic industry of social and economic development.
Nickel and
nickel alloy pipe is widely used in alkali industry, chlor-alkali chemical industry and organic chloride production, food processing industry, high temperature halogen and salt corrosion environment, water treatment, various strong alkali resistance equipment and other industries. At present, nickel and
nickel alloy tube at home and abroad are mainly seamless extrusion tube, seamless tube manufacturing process is complicated, product quality is unstable, wall thickness is not uniform, inner surface brightness is low; Compared with seamless extruded
nickel tube, welded nickel tube has the advantages of simple manufacturing process, high qualified rate and low cost.
The pure nickel straight seam welded pipe is naturally formed by the gradual bending of the row roller forming machine. The
nickel strip is continuously and gradually bent longitudinally from the end to the middle to the tail into a U-shaped cylinder, and finally forms an O-shaped cylinder, which is welded at the closest place 5~10mm from the extrusion cylinder. The forming and process of nickel straight seam welded pipe includes feeding → uncoiling → forming → welding → full circle → fixed size cutting → collecting → follow-up procedure detection, among which, welding is the most important part to ensure the quality of nickel tube. Defects such as cracks, pores, and poor fusion are easy to occur in pure nickel welding. Therefore, the experiment proposed to adopt plasma +TIG double gun welding N6 pure nickel tube longitudinal seam, make full use of the advantages of plasma and TIG welding methods, realize the stable forming of the front and back of the weld, and the mechanical and organizational properties of the joint can meet the actual production needs.
(1) The optimal welding process parameters are obtained through orthogonal test analysis: welding speed 180mm/min, PAW current 180A, TIG current 240A, distance between two guns 120mm, and verification test is carried out. The results show that under the optimal welding process parameters, the tensile strength of welding joint reaches 90% of the base metal tensile strength. Obviously higher than other process parameters.
(2) By analyzing the SEM morphology of the fracture of the welded joint with the optimal welding process parameters, it can be seen that the fracture of the welded joint is a mixed fracture dominated by ductile fracture, while the pure nickel base metal is a ductile fracture, and the elongation of the welded joint is smaller than that of the base metal.
(3) By analyzing the microstructure and hardness of plasma +TIG welding joints, the following conclusions can be drawn: N6 base material is single-phase austenite structure, the TIG welding zone of the weld is mainly composed of coarse austenite columnar crystals due to twice heating, and the plasma welding zone of the weld is composed of coarse austenite cellular crystals. The microhardness of plasma welding zone of weld is higher than that of TIG welding zone of weld, and the average microhardness of weld zone and heat-affected zone of yuan welding joint is lower than that of base metal.
(4) Plasma +TIG double gun welding of pure nickel N6 is an ideal welding method, the front and back of the weld is well formed, and the microstructure and properties of the joint can meet the actual production requirements.
