One pipe welded air duct is a pipeline formed by welding two types of steel strips, galvanized and stainless steel. The welding joint is tightly sealed and can pass through water without leakage, ensuring that customers use air ducts without oil or water leakage. The service life of the air duct is more than 10 years, and it is suitable for medium and high pressure exhaust and dust removal systems and waste gas treatment systems. The air duct can be made into 2.44 meters, 3 meters, 6 meters, and 8 meters in one connection (it is recommended to use 2.44 to 3 meters in one section). Welded air ducts are widely used in factories and industrial production. Welded air duct, also known as welded pipe, is a steel pipe with a fixed length of 6m made by pressing and forming steel plates or steel strips. It has the advantages of simple production process, high production efficiency, multiple varieties and specifications, and low equipment investment, but its comprehensive strength is lower than that of seamless steel pipes.
Preparation before welding
(1) According to the thickness form of the plate, the groove processing adopts machining plasma arc cutting or carbon arc air gouging. When using carbon arc air gouging and manual arc welding to avoid damage from splashing metal, lime powder should be applied on both sides of the groove.
(2) V-shaped grooves should be used, and the welding current should be small to prevent intergranular corrosion of stainless steel.
(3) In order to meet the same performance of joints, the selection of welding materials should follow the principle of "equal composition". At the same time, it should be noted that the ferrite content in the welded joints of air ducts should not be too high to improve the joint's ability to resist thermal cracking and intergranular corrosion.
(4) Strict positioning welding is adopted, following the principles of "short and thick" and "non penetration spot welding".
Welding technical requirements
(1) Manual arc welding adopts DC reverse connection, while argon arc welding adopts DC connection.
(2) Before welding the air duct, brush off the oxide layer on the surface of the welding wire with stainless steel wire, clean it with acetone, then air dry and use it at any time.
(3) When backing welding, the thickness of the weld seam should be as thin as possible, which is conducive to good fusion with the root; When extinguishing the arc, it should be in a gentle slope shape. If there is any arc stopping shrinkage hole, it should be polished off with a polishing machine. Arc initiation and extinguishing must be carried out within the groove, and the arc crater must be filled to prevent cracking.
(4) To prevent carbide precipitation sensitization and intergranular corrosion, the interlayer temperature and post weld cooling rate should be strictly controlled, and the interlayer temperature should be controlled below 60 ℃.
(5) When welding, try to use argon arc welding handle technology as much as possible. This process can control the surface color and shape of the welding layer, and the welding effect is ideal.
Spiral welded air ducts, welds and their edges should avoid drilling. Then, after welding, the slag at the weld seam should be removed, and the metal luster should be brushed with a stainless steel wire brush or copper wire brush. Then, acid pickling paste should be used for passivation, and hot water should be used for cleaning.