About the industrial steel Flange Classification, Assembly, and Connection

First, What is a Flange?

A flange, also called a flange plate or flange, is a disc-shaped metal body with several holes around its perimeter for connecting other components. It is widely used in various mechanical equipment and steel pipe connections. Flanges are connecting parts between shafts, used for connecting steel pipe ends; they are also used on equipment inlets and outlets for connecting two pieces of equipment, such as speed reducer flanges.

Second, Flange Assembly

1. Before assembling a flange, the flange surface, especially the sealing surface, must be cleaned.

2. When assembling a flat welded flange, the steel pipe end should be inserted into the flange's inner diameter by 2-3 mm, and then the flange should be tack welded to the steel pipe. If it is a horizontal steel pipe, the flange should be tack welded from above, and then the flange position should be checked and corrected from different directions using a 90° angle gauge, ensuring that its sealing surface is perpendicular to the centerline of the steel pipe. The second tack weld should then be correct.

3. Use a 90° angle gauge to check and correct the flange position from left to right. After passing through the third and fourth points, tack weld to complete the flange tack welding and fixing.

4. Regarding flange assembly, the bolt holes of the mounting flange should be aligned with the corresponding bolt holes of the fixing flange and parallel to the fixing flange. The deviation should not be less than 1.5% of the outer diameter of each flange and should not exceed 2mm.

5. When selecting matching flanges for equipment or valve components, attention should be paid to whether the flanges of the original equipment or valve components are consistent with the flange connection dimensions used in the steel pipe.

Third, Flange Connection

1. Flange connections should be kept on the same axis. The center deviation of the bolt holes should not exceed 5% of the hole diameter, and the bolts should be able to pass freely through the holes. The connecting bolts of the flanges should be of the same specification, installed in the same direction, and tightened symmetrically and evenly.

2. Different thicknesses of beveled washers should not be used to compensate for flange non-parallelism. Double washers should not be used. When large-diameter washers need to be spliced, they should not be butt-jointed with flat ports, but should be in the form of beveled rings or labyrinths.

3. To facilitate flange installation and disassembly, the tightening distance between the bolts and the flange face shall not be less than 200 mm.

4. When tightening bolts, symmetrical and intersecting tightening should be performed to ensure even stress on the gaskets.

5. Bolts and nuts should be coated with molybdenum disulfide, graphite oil, or graphite powder for subsequent removal: stainless steel, alloy steel bolts and nuts; steel pipes designed for temperatures below 100℃ or 0℃; outdoor installations; atmospheric corrosion or corrosive media.

6. Copper, aluminum, and mild steel gaskets should be annealed before installation.

7. Direct burial of flange connections is not permitted. Buried steel pipe flange connections should have inspection wells. If burial is necessary, corrosion protection measures should be taken.