The selection of welding methods for thick-walled steel pipes should be based on the material and wall thickness of the pipe. Different welding methods have different arc heat and arc force, and therefore different characteristics. For example, tungsten inert gas (TIG) welding is characterized by lower current density, stable arc combustion, and good weld formation, making it particularly suitable for thin-plate welding, but not for thick-plate welding. Plasma arc welding is characterized by high arc column temperature, high energy density, good arc straightness, and a wide range of adjustable rigidity and flexibility, and it is stable in operation, but it is more complex to operate. Submerged arc welding has the characteristics of high penetration depth and high wire deposition rate, thus greatly increasing welding speed and lowering welding costs, but the working conditions and environment are relatively poor. Therefore, different welding methods have different capabilities and different operating costs. Appropriately selecting the welding method based on the material and wall thickness of the thick-walled steel pipe is a very important task to ensure welding quality, improve productivity, and reduce costs.
Pickling thick-walled steel pipes is a method of removing oxide scale and rust from the steel surface using acid solutions. Acids used for pickling include sulfuric acid, hydrochloric acid, phosphoric acid, and mixed acids. The pickling process removes surface oxide scale, followed by lubrication treatment before further processing, such as drawing. If thick-walled steel pipes are not pickled, their surfaces may contain oxides and oil, which the phosphating solution cannot remove, resulting in lower phosphating quality. Furthermore, during the manufacturing process, thick-walled steel pipes undergo multiple processes, and even slight negligence can leave scratches on the surface, reducing the corrosion resistance of components and directly affecting their service life.
What detailed treatments are required before using thick-walled steel pipes?
1. Thick-walled steel pipe cutting: Based on the required pipeline length, the pipe should be cut using a metal saw or a toothed saw. When using water welding during cutting, appropriate protective measures should be taken for the raw material. During cutting, fire-resistant and heat-resistant baffles should be used at both ends of the cut to catch sparks and hot molten iron, protecting the original plastic layer of the raw material.
2. Thick-walled steel pipe connection: After plastic coating is applied, connect and install the pipes and fittings. During connection, place rubber gaskets between flanges and tighten bolts until a seal is achieved.
3. Thick-walled steel pipe plastic coating treatment: After grinding, use oxygen and C2H2 to heat the pipe ends externally until the internal plastic layer melts. Then, a technician will evenly apply the prepared plastic powder to the pipe ends, ensuring thorough application. For flanges, the plastic coating should extend above the waterstop line. Strict temperature control is crucial during this process. Excessive heat will cause bubbles during coating, while insufficient heat will result in incomplete melting of the plastic powder. Both of these issues will lead to plastic coating peeling after the pipes are put into use, and subsequent corrosion and damage to the thick-walled steel pipe.
4. Thick-walled steel pipe end grinding: After cutting, use an angle grinder to grind the plastic layer at the pipe ends. This is to prevent the plastic layer from melting or even burning during flange welding, which could damage the pipe. The plastic coating on the pipe opening is ground using an angle grinder.
To improve the corrosion resistance of thick-walled steel pipes and extend their service life, they require pickling and passivation surface treatment to form a protective film. Thick-walled steel pipes have high hardenability, good machinability, moderate cold deformation plasticity, and weldability. Furthermore, the steel’s toughness decreases only slightly during heat treatment, but it retains considerable strength and wear resistance, especially high toughness after water quenching. However, this steel is highly sensitive to white spots, exhibits temper brittleness and overheating sensitivity during heat treatment, and possesses high strength, hardenability, and toughness. It shows minimal deformation during quenching and high creep strength and long-term strength at high temperatures. It is used to manufacture forgings requiring higher strength than 35CrMo steel and with larger tempered cross-sections, such as large gears for locomotive traction, turbocharger drive gears, rear axles, heavily loaded connecting rods, and spring clips. It can also be used for drill pipe joints and fishing tools in oil wells below 2000m and for bending machine dies.
Post time: Mar-03-2026