What are the details of the large-diameter steel pipe before use?

The welding method of large-diameter steel pipes should be selected according to the material and wall thickness of the large-diameter 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. It 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 , Plasma arc has good straightness, its rigidity and flexibility have a wide adjustment range, and work is stable, but the operation is more complicated; submerged arc welding has the characteristics of penetration ability and high welding wire deposition rate, so the welding speed It can be greatly improved, 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 large-diameter steel pipes, a reasonable selection of welding methods is a very important task to ensure welding quality, improve productivity, and reduce costs.

Large-diameter steel pipes are pickled using an acid solution to remove oxide scale and rust on the surface of steel, called pickling. Acids for pickling include sulfuric acid, hydrochloric acid, phosphoric acid and mixed acids. The pickling process is to remove the surface oxide scale, and then go through lubrication treatment (carbon steel-phosphorous saponification, stainless steel-butter lime, copper and aluminum pipe-oiling), using the old technology-copper plating), and then deep drawing processing. If large-diameter steel pipes are not pickled, there may be oxides and oil stains on the surface, and the nuclear energy of the phosphating liquid cannot remove them, and the quality of phosphating will be reduced. Moreover, in the manufacturing process of large-diameter steel pipes, after many procedures, if you are not careful, it will leave scars on the surface of large-diameter steel pipes, which will reduce the corrosion resistance of parts and directly affect the service life.

1. Cutting of large-diameter steel pipes: According to the actual pipe length required, 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, fire-resistant and heat-resistant materials should be used as baffles at the two ends of the fracture to catch the sparks and hot iron water beans that fall during cutting to protect the raw materials. The original plastic layer.

2. Connection of large-diameter steel pipes: After the plastic repair is completed, connect the pipes to the pipe fittings and install rubber pads between the flanges during the connection process, and tighten the bolts to the sealed state.

3. Plastic coating treatment for large-caliber steel pipes: After polishing, use oxygen and C2H2 to heat the pipe mouth outside the pipe until the inner plastic layer is melted, and then the skilled worker will evenly apply the prepared plastic powder to the pipe mouth , It should be noted that it should be smeared in place accordingly, and the flange should be smeared 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 during the plastic coating process. The above conditions will produce plastic after the pipeline is put into use. The phenomenon of layer peeling, the later large-diameter steel pipe part of the pipeline was corroded and damaged.

4. Grinding of large-diameter steel pipe nozzles: After cutting, an angle grinder should be used to polish the plastic layer of the nozzle. The purpose is to prevent the plastic layer from melting or even burning during flange welding and destroying the pipe. Use an angle grinder to polish the plastic layer of the nozzle.

In order to improve the corrosion resistance of large-diameter steel pipes and prolong the service life of products, the large-diameter steel pipes need to be pickled and passivated surface treatment to form a protective film on the surface. Large-diameter 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 it is water quenched. It has high toughness; but this steel is highly sensitive to white spots, has a tendency to temper brittleness and overheat sensitivity during heat treatment, has high strength, hardenability, good toughness, small deformation during quenching, and high creep strength at high temperatures And long-term strength. 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, connecting rods and spring clips that are heavily loaded, and can also be used Drill pipe joints and fishing tools for oil deep wells below 2000m, and can be used for molds of bending machines.

Tips:ASTM A500-Standard Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes.According to ASTM A500, the weld seam location for square, rectangle and other specially shaped tubing shall not be located within the corner radius, unless specified by the customer or manufacturer.Under ASTM A500, the corner radius for square and rectangular tubing shall not exceed three times the corner radius.


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