3 way valve seizing in service

[SteveSP58]

I am working at a power plant in Nigeria.
I need assistance diagnosing the reason for repeated failures of a three way valve Size 60mm and Class 300.

The plug to stem anti-rotation pin is shearing and the valve stem thread to plug is becoming damaged. Eventually the valve stem is pulling out losing control of the valve. The valve is reported as vibrating prior to failure. This has happened 4 times in a very short time period. The most recent failure the plug to cage has seized completely after replacing all internal parts.
We operate 3 boilers with the same feed water and have had this issue only on one boiler?
Can any one make any suggestions or help?

Cheers

Steve

 

[gerhardl]

Hello StevenSP58,

Is there anything at all different between the three systems?

Will cross-changing valves with one of the OK boilers then damage the changed valve, and the repaired damaged be OK

One thought is that if the feeding water has a common pipeline for all boilers and is then split, the piping arrangement could be split in such a way that the pipeline/valve giving problems has a different feeding amount and/or pressure than the two others.

 

[Compositepro]

I can only guess that the valve is not being repaired correctly so the same problem keeps recurring. Try replacing the whole valve with a new one.

 

[georgeverghese]

In my experience, which ties up with O/G industry experience also, 3way valves in heavy duty service are not reliable - better to go for 2 separate control valves and split range the feed control signals as required.