The process fluid is not a major factor in deciding whether your trim components need Stellite hard facing.Bellows Seal ValvesThe main factors are presence of solid contaminents and more importantly the pressure drop against which the trim is controlling.Check ValvesAccording to the definition of valve trim in codeAPI, disc itself does not have to be 13Cr nor stellite. The disc surface only is included in trim.If valve body/bonnet material is carbon steel, your proposal " A105 disc having stellite surface" is of course possible unless Client specification requires 13Cr disc. Normally for small bore  valves the Vendor provide us the 13cr%+stellited(hard facing) , but as the size increases the vendor cant afford to give 13%Cr and stellite disc   he will either provide 13%CR plated with the WCB material  or WCB + stellited upon requirementfor your Info the stelliting wouldnt be complete for the disc , the part which seats with the seat surface are generally stellited.The trim components of globe control valves would not usually be manufactured from Carbon Steel, but rather from Stainless Steels. Plug ValvesStellite 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. Safety ValvesStelliting 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, Safety Relief Valvesthe decision on which depends upon the process conditions. Selection Between Ball and Globe Valve

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