API and ANSI Flanges

[KevinNZ]

Why do API flanges have higher pressure ratings than the same dimensioned ANSI flanges?

At first look this seems to because the API flanges are higher because the material used is stronger. But when I look at design procedures for flanges it is the bolting the determines the pressure holding ability of the flange and the flange thickness is designed to take the forces from the bolts/studs.

So given than API and ANSI flanges have the same bolting why are the API flanges rated higher?

What have I missed?

 

[codeeng]

What API standard are you referring to?

 

[KevinNZ]

API 6A

 

[unclesyd]

Here is an excellent site that has some information on the API and ANSI relationship. The online tools have some very good on makeup and identification of API flanges.
Checkout out “A Brief History” in their “Webtools”

http://www.woodcousa.com/flange_history.htm

http://www.woodcousa.com/index2.html