The welding method of thick wall steel pipe should be selected according to the material and wall thickness of thick wall 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. It is especially suitable for thin plate welding, but thick plate welding is not a choice. The plasma arc is characterized by the high temperature of the arc column, high energy density, good straightness of plasma arc, wide adjustment range of rigidity and flexibility, and stable operation, but more complex operation; Submerged arc welding has the characteristics of deep penetration ability and high wire melting rate, so the welding speed can be improved, the welding cost is lower, 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 pipe, a reasonable selection of welding methods is very important to work to improve welding quality, improve productivity and reduce costs.

Pickling of thick-walled steel tubes is a method that uses an acid solution to remove oxide skin and rust on the surface of the steel. Pickling acids include sulfuric acid, hydrochloric acid, phosphoric acid, and mixed acid. The pickling process is to remove the surface oxide skin, after lubrication (carbon steel - phosphorus saponification, stainless steel - tallow lime, copper aluminum tube - oil), with the old process - copper plating), and then pull deep processing. If the thick wall steel pipe is not pickled, there may be oxides and oil stains on the surface, and the phosphating liquid nuclear energy can not remove them, and the phosphating quality will be reduced. And the thick wall steel pipe in the manufacturing process, after multiple processes, if a little attention, will leave scars on the surface of the thick wall steel pipe, so that the parts can reduce the corrosion resistance, directly affecting the service life.

What details should be processed before a thick wall steel pipe is used

1. Thick wall steel pipe cutting: according to the actual required pipeline length, the pipe should be cut with a metal saw or toothless saw. When water welding is used in the cutting process, there should be corresponding protection methods for the raw materials. When cutting, 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, so as to protect the original plastic layer of the raw materials.

2. Thick-walled steel pipe connection: After filling the plastic, connect the pipe and pipe fitting, add a rubber pad between the flange in the connection process, and tighten the bolt to the sealed state.

3. Coating plastic treatment of thick-walled steel pipe: After grinding, use oxygen and C2H2 to heat the pipe mouth outside the pipe until the internal plastic layer is melted, and then technical workers will evenly smear the pipe mouth with prepared plastic powder. Attention should be paid to the corresponding smearing in place, and the flange plastic coating should be smearing above the water stop. The heating temperature should be strictly controlled in this process. If the temperature is too high, there will be bubbles in the plastic coating process. If the temperature is too low, the plastic powder will not melt in the plastic coating process.

4. Polishing of thick-walled steel pipe mouth: after cutting, the plastic layer of the pipe mouth should be polished by an Angle grinder, which aims to avoid melting and even burning of the plastic layer during flange welding to damage the pipeline. Use an Angle grinder to polish the plastic layer of the pipe mouth.

In order to improve the corrosion resistance of thick-walled steel pipes and prolong the service life of products, pickling and passivation surface treatment of thick-walled steel pipes are needed to form a protective film on the surface. The thick-walled steel pipe has higher hardenability, good machinability, medium cold deformation plasticity, and weldability. In addition, the toughness of steel is not reduced much during heat treatment, but it has quite high strength and wears resistance, especially since the toughness is still high during water quenching. However, the steel has a high sensitivity to white spots, tempering brittleness tendency and overheating sensitivity during heat treatment, high strength and hardenability, good toughness, small deformation during quenching, high creep strength, and long-term strength at high temperatures. It is used for manufacturing forgings that require higher strength and larger tempering section than 35CrMo steel, such as big gear for locomotive traction, turbocharger transmission gear, rear shaft, connecting rod, and spring clamp with a large load, it can also be used for drilling pipe joints and fishing tools in deep oil Wells below 2000m, and can be used for the mold of bending machine.