I would assume the PiP is required for some purpose.
If the annulus fills with water, that purpose has now been breached and hence the pipe has essentially failed and will need to be withdrawn from service / repaired / replaced, otherwise why have the Pipe in pipe in the first place?
As such the requirement for CP of the internal pipe is ludicrous and serves no purpose. Point out these salient facts to the DOT. Of curse if your pipie can actually survive and continue in operation after such an event then you're in trouble.
In any event CP only works when there is a current circuit. I there is no water there is no circuit and no corrosion.
You could always just clamp on a few anodes and pretend that the inner pipe is in open sea, but I guess it is bare pipe and the anode size would be huge.
Unfortunately Pipe in Pipe ( a drawing would be good to see exactly what you mean) is not covered in any design code or document and therefore needs some adjustment of standard design thinking. Clearly this is currently beyond whoever at the DOT is coming up with that, but you need to engage them and point out the error of their ways.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
