Passing issue from control valve (Globe)

We replaced the seat of Fisher Control valve HPT Size 6 inch S/N 18591010 HPT globe valve NPS 6 Rating : CL 1500 / 3750 PSI CWP. due to passing issue.

However after six months, again passing started. As the utility is to control drum water level, there is excessive throttling in line with variation of steam generation requirement from the HRSG unit. Gradually passing has increased to level of ~130 t/h over 2 years time.

From understanding that the amount of valve movement should not adversely affect the life of the throttling portion of a control valve, but it will affect the time between packing failures. However we are not experiencing packing leakage from the valve.

Can suggest if anyone else has experienced same thing and is this related with suspected flashing/cavitation or erosion issue?
I thought maybe a steam guy would answer this, but if no one in 6 days tries, I'll offer some observations. I'm not a steam guy I've only gotten involved to some extent when someone put a DP flow meter on a steam line. Here are several steam issues I've run into or heard of.

1. Does the steam have any superheat or is the operation at assumed saturation; but in reality the steam is wet so there's condensate droplets which impact and erode the valve trim surfaces at high velocity?

2. Is there a strainer downstream and are its internals intact, or like the one I saw, has its guts, the strainer element, been removed and never replaced so there's no filtering action and the valve trim is encountering erosion from scale that passes through a non-functioning strainer?

3. A colleague encountered a steam line where the valve outlet did not increase in diameter. Apparently the increase reduces velocity and the relatively high velocity that was not reduced by an increase in downstream pipe diameter caused noise and cavitation, as I heard it. There was room for 6m of pipe downstream and installing a larger diameter solved the noise problem.

4. Have you compared your current process conditions to the design process conditions?

Was the valve originally sized for an upstream P1 of x bar which has since, over the years been increased by some factor so that DP the valve now needs to create is excessive for its trim design?

Have you approached Fisher about sizing a valve for the current process conditions to see what their sizing program comes up with, compared to what the valve is that is installed? Their sizing programs are reputed to be very good at catching cavitation and noise situations. If the process has changed over time, it might well warrant a trim change.