How to Prevent Corrosion of Tank Vents

[smarts]

We need to replace vent on large tank used for chlorination and storage. About 6 months ago, we installed vent made of bare SS304 and it already shows significant corrosion (rust and pitting). We want to avoid paint finishes. We are considering SS316L, AL6XN, or Aluminum. How should we decide? A 12-month field test is not OK. Thanks in advance

 

[semo]

Is PVC an option? With a couple pvc 90's you can make a downturn and screen the end.