The Longneck flange, also known as the hubbed flange, is mainly used to connect pipe and pipe, has been widely used in the petrochemical industry, water supply and power systems and other fields. There are mainly two kinds of circular welding between high-pressure long neck butt welding flange and steel pipe, namely manual gas shielded welding and automatic swing gas shielded welding.
Some manufacturers use the inner and outer submerged arc welding ring welder to complete the circular welding between the long neck butt welding flange and steel pipe, that is, the double-side penetration welding is used for the welding parts, and there is no need for root cleaning treatment. At present, the two-side submerged arc welding with a minimum diameter of 300 mm or so can be realized.
The groove between the high-pressure long neck flange and the steel tube should be selected according to the welding process, with a certain weld gap and blunt edge reserved, so as to ensure the weld can be completely melted and prevent the root from burning through 0 ~ 2 mm can be reserved for the butt clearance and 0 ~ 2 mm can be reserved for the blunt edge. The corresponding clearance of submerged arc welding can be reserved 0 ~ 1mm, and the blunt edge should be less than 7mm.
The welding material shall ensure the strength, toughness and plasticity of the welding seam and match the performance of the base material. High-pressure flange material is generally A105 carbon steel, gas shielded welding (GMAW) er50-X wire can be used. The welding of the manufacturing unit shall be in strict accordance with the steel structure welding process standards.
Generally, Tack welding shall be no less than 3 points and shall be evenly distributed.
(1) The surface of the base material should be uniform, smooth and clean, and free from the burr, crack, oxide scale, rust, oil, water and other impurities.
(2) The thickness of the positioning weld shall not be less than 3 mm, and shall not exceed 2/3 of the height of the designed weld, the length shall not be less than 40 mm, and the spacing shall be 200 ~ 300 mm.
(1) Wind speed ≤2 m/s during gas welding.
(2) Air relative humidity ≤80%.
(3) The surface of the welding parts shall be kept dry.
(4) The welding environment should be at room temperature, that is above 0℃.
Preheating and interchannel temperature control
(1) Preheating temperature and inter-channel temperature shall be determined or tested comprehensively according to the chemical composition of steel, joint state, heat input value, the hydrogen content of deposited metal and welding method.
(2) The lowest inter-channel temperature in the welding process should be larger than the preheating temperature, and the highest inter-channel temperature is ≤230℃.
The difference between the maximum and minimum widths of the weld shall not be greater than 4.0mm within any 50 mm weld length range, and the deviation shall not be greater than 5.0mm throughout the weld length.