JIS B2220 SOH FLANGE tells you that the other meaning of the national standard flange is that the flange produced according to the size and tolerance range required by the national standard is different from the flange produced not according to the standard size, also called the second standard flange. (Some people call non-standard flanges incorrect.) Usually, some unscrupulous merchants will reduce the thickness and outer diameter of the flange to save materials, and use scrap steel or scrap steel to process flanges.

JIS B2220 SOH FLANGE tells you that usually, this national standard flange steel is a waste material with substandard chemical composition and mechanical properties. What's more, flanges are produced by private steelmaking in black steel mills. The steelmaking technology used in private steelmaking Obsolescence cannot guarantee mechanical properties and weldability.
JIS B2220 SOH FLANGE tells you that when using this kind of scrap that does not meet the standard, it may not be able to weld with the steel pipe, or the steel itself will leak water after welding with cracks and pores. Therefore, try to use national standard flanges when purchasing flanges.
JIS B2220 SOH FLANGE tells you that if you have limited funds and choose a second standard flange, you must carefully observe and measure the flange size.
The above information is the JIS B2220 SOH FLANGE manufacturer's introduction and analysis of the GB flange, hope it helps you.