Ball valves get jammed in service becasue os some foreign particles between seat and ball, how we can overcome to this issue, is there any method to do in service (on-line)?
It depends on the manufacturer.  All but the least expensive flanged valves have grease-injection ports that can be used to pump a sealant into the seats that can flush away debris.  Another reason to purchase specific valves instead of letting your parts house sell you junk.
I've never seen a ball valve being jammed by foreign particles in the seat.  I don't mean to say that it can't happen.  All the cases I've seen are of the seat and/or ball being scraped/gouged by foreign particles.  The mechanism to turn the valve provides enough torque to force the particles into and through the seat material, or the ball surface in the case of metal-seats.
I have seen trunnion-type ball valves jammed by foreign particles in the bottom trunnion bearing.  They get in between the trunnion stem's surface and the bearing face and just jam in there, gouging up the trunnion stem until there is just so much stuff packed in there that it locks up.  I've seen gear operators break gear teeth, valve stems twist off, actuator seals blown, etc.

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