Sand level in the process fluid is 250 PPM. Fluid is sour Oil and Gas mixture.

1)Does the ball and seat require Tungsten Carbide coating?

2)What are the criteria to select Tungsten Carbide coating?

3)Are there any less expensive alternatives for TC?

4) Suppose one compares x750 or 718 material versus TC coated 316L in the above application, which is better?

A ball valve is not for throttling, therefore it should be 100% open and not really subject to sand wear on the ball exterior or seats.  Sand should be flowing through without impinging on the ball surface as it would in an open condition.  

 I didn't say they wern't special pattern balls.  Heck maybe there's a special reverse acting check valve too, but unless you buy a special pattern, balls ARE made for on/off.  OK I just guessed its a gathering system from the header [2 phase, sand, oil, gas, H2S], so I wouldn't want to use a "special" anything in/near a gathering system, where they probably don't need to be throttling something anyway, never mind with a rubber lined special pattern ball control valve.  He didn't say it was hot, but all wells are hot these days, so the rubber would probably melt too.  If I wasn't worried about all of that, I'd still have to worry about somebody just walking off with an expensive, special pattern, rubber lined, ball, control?, valve left out in a gathering system.  All in all I'd just make sure a normal, plain old, cheap, easy-to-replace-if-necessary, ball valve was either open or closed and leave it at that. IMO.

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