Compatibility of "Penguard Midcoat" with "Penguard HB"

Dear All,
This is regarding Jotun Paints. I am going to use "Penguard Midcoat" as intermediate coating of a paint system for a steel penstock (piping) exterior. What primer should I apply before the intermediate coating. Could I use "Penguard HB" as a primer for the system. In data sheets Jotun gives Zn rich primers for the "Penguard Midcoat". But they are not talking about other systems. How should I select a one? Could any one help me?

The environmental category is C5-I.

Thank you.
BR,