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.

The process fluid is not a major factor in deciding whether your trim components need Stellite hard facing. The main factors are presence of solid contaminents and more importantly the pressure drop against which the trim is controlling.

The trim components of globe control valves would not usually be manufactured from Carbon Steel, but rather from Stainless Steels.

Stellite is a hard facing material that is applied as weld deposit overlay on another trim material like 316 SS.

So WCB /A105 carbon steels, would not typically undergo Stellite hard facing. Stelliting is not always applied to trim components, when applied in globe control valves it can either be applied to the seating faces of the plug and seat or the applied applied to all faces of the plug and internal faces of the seat, the decision on which depends upon the process conditions.

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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