Molding method for manufacturing large diameter lsaw steel pipe are UOE molding method, a row of roll forming method (CFE), CE molding. For the vast majority of the final steps of the molding process is to conduct a post-weld tube expanding full-length, in order to improve the quality of welded steel pipe shape. Expanding become large-caliber Longitudinal production to ensure the quality of the finished tube an important process. Expanding is a use of hydraulic or mechanical means from urging the steel pipe along the pipe wall bulged radially outward pressure molding process. Mechanical than hydraulic mode, the device is simple and more efficient, the world's most advanced large-caliber Longitudinal several enlarged diameter pipeline system processes are adopted, the process is as follows: Mechanical expanding the use of the split-side portion of the enlarged diameter of the segments radially expand, so the tube along the longitudinal direction in a stepwise manner to achieve the full length of the tube segments of plastic deformation process. It is divided into five stages 1. Initial stage full circle. Segments open until all the segments are exposed to the pipe wall, this time within the range of steps at various points within the steel tube radius are almost identical, steel preliminary full circle. 2. The nominal inside diameter of the stage. Segments from the front position began to decrease velocity, until you reach the desired position, this position is within the quality requirements of the finished pipe circumferential position. 3. Springback compensation stage. Segments in position to start the second stage further low speed until you reach the desired position, this position is within the missile complex process design requirements of previous pipe circumferential position.

Due to the high hardenability and strengthening the role of alloying elements, some high strength martensitic stainless steel, high speed tool steel and high-strength alloy steel. Often in the quench (or tempering) after a high-temperature tempering, the steel carbide appropriate aggregation obtain coarse carbide particles tempered sorbite organization (with ball annealing similar organizations) Thus, this delivery steel state has good cutting performance cooling directly after delivery, known as hot rolling or forging state, after hot rolling or forging steel and not subject to special heat treatment. Hot rolling (forging) termination temperature is generally 800-900 ℃, after the general natural cooling in the air, and thus hot rolling (forging) state corresponds to normalizing. Unlike strict normalizing heating temperature control, the difference because of hot-rolled (forging) termination temperature high and low. Thus it is well done microstructure and properties of the steel shaken ratio. 1. That many steel companies controlled rolling, since the finishing temperature control is very strict and forced cooling after finish rolling to take measures so that grain refinement of steel, delivery of steel with high mechanical properties. Since the appearance of the skin is covered with a layer of iron oxide, which has a certain degree of corrosion resistance, as stringent storage requirements are not kept cold drawn (rolled) state delivery of steel, medium-sized steel, thick steel plate can be in the open air yard or through thatch cover and store the non-twist and controlled cooling hot rod location is the truth, hot-rolled (forging) state of delivery than ordinary steel hot rod performance. 2. Cold drawn (rolled) on steel hardenability without any heat treatment and direct delivery, the status of the cold drawing, cold-rolled steel cold forming. Called cold-drawn or cold-rolled condition. Cold-drawn steel dimensions (rolled) state of high accuracy, good surface quality, appearance roughness is low, and have high mechanical properties, compared with the hot rolling (forging) state. Since the cold drawn (rolled) state of delivery without scale steel outer cover, and there is a big stress, vulnerable to corrosion or rust, and thus cold drawn (rolled) state steel, packaging, storage and transportation are more stringent requirements, generally need to be in the custody of the Treasury, and the Treasury should pay attention to the temperature and humidity control the delivery state within the state, said normalizing. Since normalizing heating temperature (hypoeutectoid steel as Ac3 + 3050 ° C eutectoid steel as Accm + 3050 ° C than hot-end temperature control strict, 3. Before normalizing the status of the steel factory and normalizing heat treatment. Thus the structure of the steel, a uniform performance. Since normalizing cooling faster, compared to steel annealed state. Pearlite structure of the steel increased number of pearlite lamellar and grain refinement of steel, and thus have higher mechanical properties, and help to improve the low carbon steel widmanstatten and eutectoid steel cementite net, for further heat treatment of the finished product do organizational readiness.