Flange is a part connected between shaft and shaft, which is used to connect pipe ends. Flanges are also used in the import and export of equipment, for the connection between the two equipment, such as blind flanges and threaded flanges. Flange has good comprehensive performance, so it is widely used in chemical engineering, construction, fire protection, electric power, aerospace and other basic engineering. To have a more profound understanding of the flange, notices for flange welding process and flange connection will be shown in the following.

Flange Welding Technology

1. Preparation before Welding

(1) You should check debugging equipment to ensure normal operation of equipment.

(2) You should prepare welding rod of φ4.0J402, preferably drying at 300-350 ℃ for one hour.

2. Welding Process

(1) The vertebral body and socket weld flanges are assembled together according to the requirements of the drawing, and the socket weld flange should be divided into eight equal parts on average.

(2) Because the long weld neck flange is thicker and the groove is bigger, the segmental and symmetrical welding should be adopted.

3. Weld Quality

The welding strength should be at least as high as the base metal strength. The surface of the weld should be smooth. There are no defects such as burning, blowhole, welding leak, slag inclusion and undercut and so on. The residual height is less than 2 mm.

4. Considerations

(1) J506 electrode and low current welding must be used for manual surfacing. And you should strictly follow the welding process.

(2) After each welding position, the deformation of plate flanges should be calibrated with a horizontal ruler.

(3) While welding, you should hammer the weld with air hammer to eliminate the stress.

 

Notices for Flange Connection

1. Flange connection should maintain the same axis. The center deviation of bolt hole is generally less than 5% of the hole diameter, and the bolt should be guaranteed to penetrate freely. The connecting bolts of lap joint flanges should be of the same specification. The installation direction should be the same, and the bolts should be tightened symmetrically and evenly.

2. Inclined gaskets of different thickness should not be used to compensate for the non-parallelism of flanges. Double washers should not be used. When large caliber gaskets need to be spliced, they should not be butted with flat caliber, but with oblique lap or labyrinth.

3. For the convenience of installing and disassembling slip on flanges and fastening bolts, the distance between the flange plane and the wall should not be less than 200 mm.

4. When tightening the bolt, it should be carried out in symmetrical and intersecting order to ensure that the gasket bears uniform force.

5. When encountering the following cases, bolts and nuts should be coated with molybdenum disulfide, graphite oil or graphite powder.

(1) Stainless steel, alloy steel bolts and nuts;

(2) The design temperature of the pipeline is higher than 100 ℃ or lower than 0 ℃.

(3) Open-air installations;

(4)  Atmospheric corrosion or corrosive medium.

6. The metal gaskets such as copper, aluminium and mild steel should be annealed before installation.

7. Flange connecting bolts for high or low temperature pipelines should be tightened in hot or cold state in accordance with the following provisions during trial operation:

(1) Tightening in hot or cold state should be carried out after 24 hours of working temperature.

(2) When fastening pipe bolts, the maximum internal pressure should be determined according to the design pressure. When the design pressure is less than 6MPa, the maximum internal pressure of hot tightening is 0.3MPa. When the design pressure is greater than 6MPa, the maximum internal pressure of hot tightening is 0.5MPa. Cold tightening should generally be carried out under pressure relief. Hot and cold tightening should be moderate, and safety measures should be taken.

8. Flange connections are not allowed to be buried directly. Inspection wells should be installed at the flange joints of buried pipelines. If it should be buried, anti-corrosion measures should be taken.