Flat welding flange is also called lap welding flange. The connection between the flat welding flange and the pipe is to insert the pipe into the inner hole of the flange to an appropriate position, and then lap welding.

According to the internal pressure calculation, the strength of the flat welding flange is about two-thirds of the corresponding butt-welded flange, and the fatigue life is about one-third of the butt-welded flange. Therefore, flat welding flanges are only suitable for pipeline systems with relatively low pressure levels and no serious pressure fluctuations, vibrations and swells.

Flat welding flanges can be subdivided into two types: neck flat welding and plate flat welding.