Welding technology of high neck flange
Neck flange, also known as long neck flange and high neck flange, is a disc shaped part, which is mainly used to connect pipes. It has been widely used in petrochemical, urban water supply and power systems. In recent years, with the planning and construction of ultra-high voltage transmission line projects in the State Grid, the demand for ultra-high voltage steel tube towers has increased dramatically.
As a new form of flange connection for steel tube tower, high neck flange has been proved to be advanced and reliable. It plays a vital role in improving the production capacity and product quality of steel tube tower.
There are two main methods for early circumferential welding of ultra-high pressure high neck butt welding flange and steel pipe: manual gas shielded welding and full automatic swing gas shielded welding.
Based on the above two welding methods, Gebie ultra-high pressure steel pipe tower manufacturer independently developed a special machine for internal and external submerged arc welding to realize the circumferential welding of high neck butt welding flange and steel pipe according to the welding process characteristics. This process uses submerged arc welding to conduct double-sided penetration welding on the workpiece, and no back gouging is required during the welding process, which maximizes the welding efficiency on the premise of ensuring the welding quality.
With the continuous production of high neck butt welding flange, the welding method and welding technology are also constantly improving. According to the specifications and dimensions of the actual workpiece, manual gas shielded welding, full automatic swing gas shielded welding or submerged arc welding and other welding schemes can be reasonably selected.
1. Tack welding
Tack welding must be performed by welders with corresponding qualification certificates. The base metal surface and both sides near the weld shall be uniform and smooth, and free of burrs, cracks, oxide skin, rust, grease, water and other impurities.
The thickness of positioned welding seam shall not be less than 3mm, and shall not exceed 2/3 of the design weld height. The length shall not be less than 40mm, the spacing shall be 200-300mm, and shall be evenly distributed.
2. Welding environment
The wind speed during gas shielded welding is less than 2m/s; Relative air humidity ≤ 80%; The surface of weldment shall be kept dry.
3. Preheating and interpass temperature control
Preheating temperature and interpass temperature shall be determined according to comprehensive factors, such as chemical composition of steel, constraint state of joint, heat input, hydrogen content of deposited metal and welding method.
4. During welding, the minimum interpass temperature shall be ≥ preheating temperature, and the maximum interpass temperature shall be ≤ 230 ℃.
At present, the production technology of high neck forged flange has gradually matured and the overall quality is good. The total qualification rate of welds is 98%, and each key quality can meet the technical requirements of steel tube tower production, but the process needs to be further solidified.