Corrosion on SS 304 welding area 5

[DixieSolar]

Dear All,

I'm developing a solar water heater which combines the collector and storage tank together, heating portable water directly. The product has been made, and tested. The problem we found after 6 months testing is pitting/crevice corrosion on the top of SS 304 tube (welding area).

My case is:
- SS 304 long tube welded on the bottom and top
- portable water in the SS tube, regular working temp. 35-210F.
- Pressure <90 psi
- Max temp. 600F when the SS tube is empty and baked under the sun.

There is very little corrosion found at the bottom or in the middle of tube. Pitting/crevice corrosion is only found at the top around welding area. The solar hot water was rarely used when testing. I suspect that the pressured steam with chlorine in portable water is causing the corrosion, and the S.S. material structure was damaged at the welding area.

My question is:
-Any coating material can be applied at the top of welding area inside the S.S. 304 tube? but it can not contaminate the portable water under high temp. and pressure.
-Any welding process or procedure can be used without destroy S.S. 304 material structure in this case?

Thank you very much for your help and advice!

Dixie Solar

 

[DixieSolar]

Thank you very much! Ed, you are very helpful!