What is the difference between vacuum butt welding flanges and vacuum flat welding flanges?

Vacuum butt welding flanges are welded together with the same diameter and wall thickness as the pipe to be welded at the interface end.
Flat welding flange is a concave groove machined at the interface slightly larger than the outer diameter of the pipe, and the pipe is welded inside.
The welding performance of butt welding is relatively good, and the corrosion is relatively small.
Flat welding and butt welding are welding methods used when connecting flanges and pipelines. When welding flat welding flanges, only single-sided welding is required without welding the inner port of the pipeline and flange connection. Welding installation of butt welding flanges requires double-sided welding of the flange.
So flat welding flanges are generally used for low and medium pressure pipelines, while butt welding flanges are used for connecting medium and high pressure pipelines. The flanges for butt welding are generally at least PN2.5MPa, and butt welding is used to reduce stress concentration. Generally, butt welding flanges are mostly neck flanges, also known as nipple flanges. So the installation cost, labor cost, and auxiliary material cost of welding flanges are higher because there is an additional process.
Not all butt welding flanges require double-sided welding both inside and outside, and there are no special requirements. Generally, only one layer is welded on the outside. Have you ever seen a 1/2 "butt welding flange? Flat welding is easier to weld because the pipe and flange are well aligned and the pipe will not tilt.