Every body can tell me if globe valve disc and seat are 13% chrome steel. It can be stellite or it doesn't need stellite .the service of valve for sweet gas.

Various issues being thrown about here, some needlessly so.  There are generally four primary reasons to use a stellited trim.
1) Fluid stream solids
2) Gallable materials
3) Process fluid
4) Excessive pressure drops across the trim

Fluid stream solids are an easy one, particulate matter in the fluid stream can damage trim surfaces, but thay also damage body surfaces too.  Both should be a concern even though the trim would be primary.

Gallable materials like 316 stainless steel can gall under high seat loads, stelliting one or both surfaces can make this go away or at least reduce it significantly.

Fluid stream material is a significant issue.  It was suggest that the process fluid has little impact, totally  untrue.  All other things being equal, a valve controlling nitrogen has a significanly better chance of survival that one contolling 300 deg F water.  Some materials are just naturally more abrasive.

And finally yes large pressure drops can create several different forms of cavitation type damage.  This is a very real issue and in some cases if the pressure drop is high enough using an abrasive fluid, stellite will not survive either.

After all of these issues are considered and with full application data, you can typically make a decent decision on the trim material.   I could help further if you need me too, I'd need more app data to provide a suggestion though.

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