Steel plate flange connection involves fixing two pipes, fittings, or equipment to their respective flange discs first, then connecting the two flange discs together with a flange gasket in between and securing them with bolts, thus completing the connection. Some fittings and equipment come with a flange disc already attached, which also falls under flange connection. The welding quality of the flange to the pipe not only affects the overall alignment of the pipeline but also impacts the strength and tightness of the pipeline connection.

The flange center should be aligned with the pipe center in a straight line.

2. The sealing face of the flat welding flange should be perpendicular to the pipe center. When DN < 300mm, a deviation of 1mm is permitted; when DN > 300mm, the deviation is 2mm.

3. Flange connections should use bolts of the same specification, with consistent installation direction, meaning nuts should be on the same side. Bolts and nuts for connecting valves are generally placed on one side of the valve components. When tightening bolts, they should be done symmetrically and evenly, with moderate tightness. The length of the bolt protruding beyond the nut after tightening should not exceed 5mm or 2 to 3 turns.

4. Flange connections should be coaxial, with the center deviation of bolt holes generally not exceeding 5% of the hole diameter, and bolts should be able to pass freely. The positions of the bolt holes on the flanges at both ends of the same pipe should match, and the positions of the bolt holes on the flange on the pipe should correspond to those on the mating equipment or pipe fittings.

5. Bolt hole positions on the flange: For bolt holes on vertical pipes, the two bolt holes closest to the wall should be parallel to the wall; for bolt holes on horizontal pipes, the two bolt holes above should remain level. Additionally, the two connecting flanges should be parallel and natural, with the parallelism deviation not exceeding 2mm.