I note that on globe and check valve the use of stellite as hard facing and corrosion resistant layer on trim parts is the best solution for many vendors.
For ball valve I see that a lot of vendor use carbon steel with Electro Nickel Plated as trim material as corrosion and hard facing layer.

Someone knows the reason of this distinction. Which is the main difference beetween this two surface treatment.
Stellite hardfacing consists of a weld overlay (so a very thick coating) of cobalt or some variation thereof whereas ENC/ENP is just a very thin coating of nickel (between 1 and 3 mils) that is applied to the ball valve ball.

It would be very expensive to provide a weld overlay on a ball valve ball and while I think there might be one or two vendors who offer weld overlays (I think Grove offers a 625 weld overlay as an option?), I've never actually seen or purchased one.

ENC/ENP coatings will be okay in many services but because they are such a thin coating, they do have a tendancy to develop scratches or other minor damage which then results in corrosion creeping back under the coating causing further damage. This usually leads to the valve weeping and allowing some product to pass when closed. You won't get 100% shutoff.

My general rule is to not accept ENC/ENP coatings for critical valves (or in sour service) but to accept them in more routine or low risk applications.  This is a personal preference and many people routinely specify them for almost all service conditions. It may have something to do with whether you have to deal with the consequences or whether you're just executing the project and handing off :)

The usual preference for ball valves, something you didn't mention, is to purchase with solid stainless steel balls. This provides good corrosion resistance and performance without the risk of scratches or other minor damage leading to more extensive problems.  Ball valves with solid stainless balls are commonly available and in fact may be the default product and less expensive product in some sizes and designs (e.g., small floating ball valves). 

Many valve companies avoid the trade names, instead prefering the generic UNS designations.  Stellite is a trade name that applies to the Deloro Stellite family of alloy materials including cobalt and nickel alloys.  Stellite alloy 6 is probably the most commonly used alloy for hard facing valves.  A dozen other Stellite cobalt alloys exist plus several stainless,  tungsten and chrome materials.  Consider more specific descriptions of the hard facing materials.

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