API650 flush type clean out fitting... gasket

[Heyner]

Hi!

I'm working in design of AST's according to API650. Code don't ask for a finished surface in bolting flange of flush-type clean out fitting. Anyway, that´s the way we have been doing it to ensure leakage will not appear.

I want to ask:
Does anybody know if the clean out fitting works without flange finishing and without leakage? if it does, what kind of gasket is to be used?

thanks,

Heyner.