Do flow sensors with metal components survive ok?

[Mike B22]

For example the Corrente flow sensor impeller pictured below. The shaft and the circlip holding the magnet in place are metal and the tip looks like some kind of ceramic although it may just be the reflection making it look that way.
Normally these things are out of sight so you wouldn't notice corrosion unless you took the thing apart for maintenance.

 

[laverda]

It really depends on what kind of metal they are. Even stainless steel will corode depending on the alloy used. Titanium is really the only thing really suitable in the long run. If they were titanium I would ecpect the manufacturer to say so.

 

[Mike B22]

I was surprised when PRS told me that the Corrente flow sensor uses 304 stainless steel. I was expecting it be be 316L at least.
304 grade isn't designed for constant salt water immersion. Even 316L grade is only recommended if the water is guaranteed to be oxygen rich so the protective oxide film is preserved.

I went searching for flow sensors that are specifically salt tolerant, but there is a lack of technical information about the materials used. It seems that vendors are just repackaging the fresh water variety for use in salt water conditions without considering the life expectancy. Inexpensive pond pumps often use ceramic bearings presumably because they don't corrode.

 

[laverda]

Ceramic bearings do not corrode and they have very good wear properties as well as low friction.