The welding method of thick-walled steel pipes
should be selected according to the material and wall thickness of thick-walled steel pipes. Because different welding methods have different arc heat and arc force, different welding methods have different characteristics. For example, tungsten arc welding is characterized by low current density, stable arc combustion, and good weld formation, which is especially suitable for thin plate welding, while thick plate welding is not an option; plasma arc is characterized by high arc column temperature and high energy density. , the straightness of the plasma arc is good, its rigidity and flexibility have a wide adjustment range, and it works stably, but it is more complicated to operate; submerged arc welding has the characteristics of high penetration capability and high welding wire deposition rate, so the welding speed It can be greatly improved, and the welding cost is low, but the working conditions and environment are relatively poor. It can be seen that different welding methods have different capabilities and different operating costs. According to the material and wall thickness of thick-walled steel pipes, a reasonable selection of welding methods is a very important task to ensure welding quality, improve productivity, and reduce costs.
Pickling of thick-walled steel pipes is a method of using an acid solution to remove scale and rust on the steel surface, which is called pickling. Pickling acids include sulfuric acid, hydrochloric acid, phosphoric acid, and mixed acids. The pickling process is to remove the surface scale, after lubricating treatment (carbon steel-phosphorus saponification, stainless steel-butter lime, copper and aluminum tube-oiling), using the old process-copper plating), and then deep processing of drawing. If the thick-walled steel pipe is not pickled, there may be oxides and oil stains on the surface, which cannot be removed by the nuclear energy of the phosphating solution, and the phosphating quality will be reduced. Moreover, in the manufacturing process of thick-walled steel pipes, after many processes, if you do not pay attention, there will be scars on the surface of thick-walled steel pipes, which will reduce the corrosion resistance of parts and directly affect the service life.
What details do thick-walled steel pipes go through before use?
1. Cutting of thick-walled steel pipes: According to the actual length of the required pipeline, metal saws and toothless saws should be used to cut the pipes. When water welding is used in the cutting process, the raw materials should be protected accordingly. When cutting, fireproof and heat-resistant materials should be used as baffles at both ends of the fracture to catch the sparks and hot molten iron beans falling during cutting, to protect the raw materials. The original plastic layer.
2. Connection of thick-walled steel pipes: after plastic repair, connect and install the pipes and fittings, add rubber pads between the flanges during the connection process, and tighten the bolts to a sealed state.
3. Plastic coating treatment of thick-walled steel pipes: after polishing, use oxygen and C2H2 to heat the nozzle outside the pipe until the inner plastic layer melts, and then the skilled workers will evenly coat the nozzle with the prepared plastic powder, It should be noted that the corresponding coating should be in place, and the plastic coating of the flange should be coated above the water stop line. In this process, the heating temperature should be strictly controlled. If the temperature is too high, bubbles will be generated during the plastic coating process. If the temperature is too low, the plastic powder will not melt completely during the plastic coating process. In the above cases, plastic will be generated after the pipeline is put into use. Layer peeling phenomenon, the later part of the pipe thick-walled steel pipe was corroded and damaged.
4. Grinding of the nozzle of the thick-walled steel pipe: After cutting, the plastic layer of the nozzle should be polished with an angle grinder. The purpose is to avoid melting or even burning of the plastic layer during flange welding and damage to the pipe. Use an angle grinder to grind the nozzle plastic layer.
To improve the anti-corrosion ability of thick-walled steel pipes and prolong the service life of products, pickling and passivation surface treatment are required for thick-walled steel pipes to form a protective film on the surface. Thick-walled steel pipes have high hardenability, good machinability, moderate cold deformation plasticity, and weldability; in addition, the toughness of the steel does not decrease much during heat treatment, but it has quite high strength and wear resistance, especially when water quenching. It has high toughness; however, this steel is highly sensitive to white spots, has temper brittleness tendency and overheating sensitivity during heat treatment, high strength and hardenability, good toughness, small deformation during quenching, and high creep strength at high temperature and long-term strength. It is used to manufacture forgings that require higher strength than 35CrMo steel and larger quenched and tempered sections, such as large gears for locomotive traction, supercharger transmission gears, rear axles, heavily loaded connecting rods, and spring clips, and can also be used for Oil deep well drill pipe joints and fishing tools below 2000m, and can be used as molds for bending machines.