We have one order from my client to supply ON/OFF valve from size 4 up to 24 inch. Application is highly sour (H2S and CO2 and water and also a little CL). Material that costumer is ordered is A186 F6a for ball and also request for fully stellited of ball.  I asked with some ball valve manufacture for fully stelliting of ball but they didn't accept and do stelitting only contact area (areas contact between ball and seat ring). They don't consider high corrosive media that cause SCC on ball. My questions are as follow:
1-    What are manufacturer's limitation for apply stellite overlay on ball?
2-    Is there another method instead of stelliting that cover corrosion and erosion concerns?
Please note that fluid is produce in well and these valve are used in wellhead facilities. Also rating of these valve are 1500#
I ask for specialist on this subject to help me to able correct decision.

The valve body (and bonnet if it is top entry) and stem are pressure retaining and require to be supplied per NACE.
The ball is not pressure retaining and not strictly required to conform to NACE.  Of course if it is closed for long periods the face of the ball will be under pressure and this part is stellited.
It makes sense to stellite the area in contact with the seats but not all of the ball.
I don't remember any reference to Stellite in NACE MR0175 ISO 15156.
Maybe some corrosion expert can help.

the issue is not due to the service.
The real problem of applying stellite on the ball is that it gests exfoliated after a while.
For this type of application on ball valves Tungstens carbide coating, applied with HVOF method, is technically better.
But if the service is really highly corrosive, then they should change the ball material to SDSS or Inconel.
Moreover if the service is that corrosive, what about the body material?
You should forsee a welding overaly in Inconel on the static and dynamic areas at least.

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