Cavitation in ball valves

[andygo11]

Hi, we have a produced water injection line into a desanding vessel. Outside the vessel, there are two control valves for the injection line. After a year, there are some pitting and general corrosion occurred downstream of the valves and in the valves. Based on our analysis, we think the pitting is caused by cavitation due to the cyclic pressure drop when closing the valve. Also, we found that, if we used a galvanized trim valve, after a year, there is no corrosion or pitting issue inside the valve. Still the bare carbon steel pipe downstream still has the issue. My question is why the galvanized coating can help the cavitation? I did some search on line. Usually, the hard materials can be an option to prevent the cavitation.

 

[Chumpes]

hi
having an idea of the material of construction is necessary for understanding of corrosion processes. I suppose it is carbon steel...
maybe it is not strictly cavitation but erosion corrosion, that would explain galvanized coated trim become resistant but not the downstream CS piping.
I save the word "pitting" for stainless steel and other resistant alloys, and not for carbon steel...
it is a bit surprising to me to see the internals of a valve in corrosive service (water) made from non resistant material...
regards

 

[Metalero]

Most likely, the diagnosis of cavitation was incorrect.

 

[andygo11]

The contractor's report is back. They said it is MIC.

 

[Metalero]

ok, it can be ...
I do not know why, but many contractors always say that bacteria are to blame for everything.
Depending on what type of MIC, it would also affect the galvanized coating.
Anyway.