The welding method for thick walled steel pipes should be selected based on the material and wall thickness of the thick walled steel pipes. Due to different welding methods having different arc heat and arc force, different welding methods have different characteristics. For example, tungsten arc welding has low current density, stable arc combustion and good weld formation, which is especially suitable for thin plate welding, but not for thick plate welding; The characteristics of plasma arc are high column temperature and high energy density The plasma arc has good straightness, wide range of rigidity and flexibility adjustment, stable operation, but the operation is more complex; Submerged arc welding has the characteristics of large penetration depth and high wire deposition rate, so the welding speed can be greatly improved and the welding cost is low. However, the working conditions and environment are relatively poor. It can be seen that different welding methods have different capabilities and operating costs. Choosing a reasonable welding method based on the material and wall thickness of thick walled steel pipes is a very important task to ensure welding quality, improve productivity, and reduce costs.
The acid pickling of thick walled steel pipes is a method of removing oxide scale and rust on the surface of the steel using an acid solution, known as acid pickling. Acid pickling includes sulfuric acid, hydrochloric acid, phosphoric acid, and mixed acid. The acid pickling process involves removing surface oxide scale, undergoing lubrication treatment (carbon steel phosphorus saponification, stainless steel butter lime, copper aluminum pipe oil coating), and using the old process copper plating, followed by deep drawing processing. If thick walled steel pipes are not pickled, there may be oxides and oil stains on the surface, and the nuclear energy of the phosphating solution cannot remove them, resulting in a decrease in phosphating quality. Moreover, in the manufacturing process of thick walled steel pipes, after multiple processes, if not paid attention, the surface of the thick walled steel pipe will appear scars, reducing the corrosion resistance of the parts and directly affecting the performance of the product. 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 or toothless saws are used to cut the pipes. When using water welding during 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 block sparks and hot iron during cutting and 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. During the connection process, add rubber pads between the flanges and tighten the bolts to a sealed state.
3. Thick walled steel pipe coating treatment: After polishing, heat the nozzle with oxygen and C2H2 outside the pipe until the inner plastic layer melts. Then, skilled workers evenly apply the prepared plastic powder to the nozzle, paying attention to the corresponding coating being in place. The plastic coating of the flange should be applied above the water stop line. During 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, plastic powder will not completely melt during the plastic coating process. In the above situations, plastic will be produced after the pipeline is put into use. Layer by layer peeling phenomenon, thick walled steel pipes are corroded and damaged in the later stage of the pipeline.
4. Grinding of thick walled steel pipe nozzles: After cutting, use an angle grinder to polish the plastic layer of the nozzle. The purpose is to prevent the plastic layer from melting or even burning during flange welding, which can damage the pipeline. Grind the plastic layer of the nozzle with an angle grinder.
In order to improve the anti-corrosion ability of thick walled steel pipes and extend the service life of products, it is necessary to perform acid pickling and passivation surface treatment on the 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 significantly during heat treatment, but it has relatively high strength and wear resistance, especially during water quenching. High toughness; However, the steel is highly sensitive to white spots, has temper brittleness tendency and overheating sensitivity during heat treatment, and has high strength and hardenability
