Can the ANSI/FCI 70.2 (IEC 60534-4) control valve seat leakage classes be applied to ball valves?  Well, OK, yes I know they can, but would a supplier/manufacturer supply/manufacture to such standards?  Is there a standard specific for ball valves?

When it comes to ball valves, yes manufactures can and will specific their leakage class as III, IV, V, etc.  Some manufacturers will state they are bubble tight.  You need to read there test proceedure on how they determine bubble tight thou.

Wasn't the original leakage class standard developed for globe control valves which are unbalanced? Trying to hold a plug down on a seat ring to provide tightness as the differential get higher is tough. Do the math... This is why class five allows more leakage per more inches of diameter per psiD.

A ball valve gets tighter with more differential across it.

Doesn't the standard also only go to 8"???

I can't count the number of times I've seen a 12" butterfly valve to class six tightness...

For high performance butterfly valves with offset design refer to MSS SP-68.  Seat leakage is covered in 5.2.2 Each valve furnished for  shutoff or isolation service shall be subjected to a seat test using fluid as described in 5.1. at 1.1 times the shutoff differential pressure rating of the valve at ambient
temperature. No visible leakage through the body or the disc or past the seat shall be allowed. Test duration shall not be less than shown in Table 4. I TABLE 4. SEAT TEST DURATION - see the standard.

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