Detailed treatment of thick-walled steel pipes before use

The selection of welding method of the thick-walled steel pipe should be selected according to the material and wall thickness of the thick-walled steel pipe. 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, but 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 the work is stable, but the operation is more complicated; the submerged arc welding has the characteristics of penetration depth and high wire deposition rate, so the welding speed It can be greatly improved, and the welding cost is lower, but the labor 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 job 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 oxide scale and rust on the surface of the steel, which is called pickling. Acids for pickling include sulfuric acid, hydrochloric acid, phosphoric acid and mixed acids. The pickling process is to remove the oxide skin on the surface, after lubricating (carbon steel-phosphorus saponification, stainless steel-tallow lime, copper-aluminum pipe-oiling), using the old process-copper plating), and then deep-drawing processing. If the thick-walled steel pipe is not pickled, there may be oxides and oil stains on the surface, and the phosphating liquid nuclear energy cannot remove them, and the phosphating quality will be reduced. Moreover, in the manufacturing process of thick-walled steel pipes, after several processes, if a little care is not taken, scars will be left on the surface of thick-walled steel pipes, which will reduce the corrosion resistance of parts and directly affect the service life.

What details should be processed before thick-walled steel pipes are used?

1. Thick-walled steel pipe cutting: According to the actual required pipeline length, metal saws and toothless saws should be used to cut the pipelines. When water welding is used in the cutting process, the raw materials should be protected accordingly. When cutting, fire-resistant and heat-resistant materials should be used as baffles at both ends of the fracture to catch the sparks and hot iron beans that fall during cutting to protect the raw materials. Original plastic layer.

2. Pipe connection of thick-walled steel pipe: After plastic repair, connect the pipe and the pipe 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 pipe: After grinding, use oxygen and C2H2 to heat the nozzle outside the pipe until the inner plastic layer melts, and then the skilled worker will use the prepared plastic powder to evenly apply the nozzle to the nozzle. , it should be noted that the corresponding application should be in place, and the flange plate should be applied to 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. The phenomenon is that the layer falls off, and the thick-walled steel pipe part of the pipeline is corroded and damaged in the later stage.

4. Grinding of the nozzle of the thick-walled steel pipe: After cutting, an angle grinder should be used to grind the plastic layer of the nozzle. The purpose is to prevent the plastic layer from being melted or even burned during flange welding, which may damage the pipeline. Use an angle grinder to grind the nozzle plastic layer.

In order to improve the corrosion resistance of the thick-walled steel pipe and prolong the service life of the product, the thick-walled steel pipe needs to be subjected to pickling and passivation surface treatment 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 steel is not much reduced during heat treatment, but it has quite high strength and wear resistance, especially when water quenched. It has high toughness; but this steel has high sensitivity to white spot, temper brittleness tendency and overheating sensitivity during hent, 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 and larger quenched and tempered sections than 35CrMo steel, such as large gears for locomotive traction, supercharger transmission gears, rear axles, connecting rods, and spring clips that are heavily loaded, and can also be used for Drill pipe joints and fishing tools for oil wells below 2000m, and can be used for molds of bending machines.