Stainless steel in septic tanks

[Jim Sanderson]

Hello, I am looking to use some stainless steel probes in a septic tank to indicate different water levels. i.e. bottom probe would be 0v then propes further up would be set at 12v and taken to 0V when the water level reaches them. Current draw will be very minimal 2 or 3 mA.

The big question I have is about corrosion of the Stainless steel contact probes. After reading varius threads on here it seems if a 316 grade bolt was used and the end that is to be exposed to the water is machined smooth and highly polished it should not corrode.

The other option, I don't need anything strong and I understand the higher the content of chromium the beter the resistance to corrosion. Can you generally buy rods of high chromium content SS and then machine it yourself?

Septic tanks would generally I assume be alkaline due to the large amount of water from dish washers and clothes although I need to do some ph tests to confirm this.

thanks, Jim.

 

[mgb_phys]

316 stainless is the most corrosion resistant common stainless - it's machinable and used for most offshore applications.

Do you have to have the probe powered 24x7?
You can reduce corrosion if you only turn it on occasionally.

 

[Jim Sanderson]

Do you have to have the probe powered 24x7?
You can reduce corrosion if you only turn it on occasionally.

Good point, I can program the controller to check every 5 minutes, so it will only be a pulse.

Do you think 316 would be suitable or should I go for something better?

 

[ty2nu]

Dont forget to galvonically isolate the probe body from the steel tank at the interface and from the power supply driving your microcontroller. Try MIL-HDBK-1004 for comprehensive overview.