The JIS B2220 SOH FLANGE tells you that a flat welding flange is a flange that is connected to a vessel or pipe by fillet welds, It is an arbitrary flange.

The JIS B2220 SOH FLANGE tells you that when designing flat welding flanges, according to the integrity of the connection between the flange ring and the straight cylinder section, check the integral or loose flange respectively.
The JIS B2220 SOH FLANGE tells you that flange rings are available with or without a neck. 
The JIS B2220 SOH FLANGE tells you that compared with the butt welding flange with the neck, the flat welding flange has a simple structure and saves materials, but the rigidity and sealing performance are not as good as that of the butt welding flange with the neck. 
The JIS B2220 SOH FLANGE tells you that flat welding flanges are widely used in the connection of medium and low-pressure vessels and pipelines.
The above information is the JIS B2220 SOH FLANGE manufacturer's introduction and analysis of the characteristics of the flange, hope it helps you.