The national standard flange is a universal part; the outer diameter, screw hole, and thickness of various specifications of the flange are fixed. Moreover, the national standard flange considers safety factors, so the size and thickness include a relatively large safety margin.
The implementation standards for standard flanges are as follows:
GB series (GB/T9119-2010 National Standard)
JB series (Mechanical Department Standard)
HG series (HG20592 Chemical Industry Standard)
ASME B16.5 (US Standard)
BS4504 (British Standard)
DIN (German Standard)
JIS (Japanese Standard)
CBM (Ship Label)
The size of the national standard flange is exactly the same across different national standards.
Stainless steel non-standard flanges are generally created by enterprises or individuals to save materials or use local materials. Typically, stainless steel non-standard flanges are designed to be smaller and a bit thinner than national standard flanges to save materials. The sealing surface form can also be changed, such as using an O-ring seal. Equipment manufacturers can design the size of the flange according to actual usage needs. General stainless steel non-standard flanges come with drawings that indicate the flange material, inner and outer diameter, center line, number of holes, hole size, thickness, and chamfering, all processed to meet specific requirements.
National standard flanges can be bought on the market, whereas stainless steel non-standard flanges must be designed and processed individually.
Stainless steel non-standard flanges are used in limited situations. For example, if an equipment cylinder flange operates at a working pressure of only 0.3MPA, it might not be necessary to use a 0.6MPA national standard flange. In this case, you could design a smaller and thinner stainless steel non-standard flange. However, you must consider whether the cost of design and processing is less than the cost savings from using less material.
General non-standard flanges come with drawings indicating the flange material, inner and outer diameter, center line, number of holes, hole size, thickness, and chamfering, processed to specific requirements.