1. That will depend on the material the valves are made from and the material and natural elements you are preserving them from (sand, water, sea water, wind, sun, oil, gas, etc.).

2. That will depend on the material the equipment is made from and the material and natural elements you are preserving it from (sand, water, sea water, wind, sun, oil, gas, etc.).

3. A corrosion coupon is a removable strip of material, identical to the system's material (or selected specifically for the system) and placed in a suitable location within the pipeline so it experiences the same exposure as the rest of the system. The coupon is removed for inspection at a specific time in order to take measurements and estimate the total system's corrosion rate from the corrosion rate of the coupon.

What are Corrosion Coupons?

Andrew H.
www.mototribology.com