Currently, rigid conduit is installed on said cooling towers and the conduit is beginning to deteriorate. I am unable to locate any information that suggests rigid conduit is not suitable for this particular situation in order to justify a recommendation for new piping. The cooling towers are also treated with some sort of bug repellant chemical.

See NEC Article 344 - Rigid Metal Conduit. It's permitted almost everywhere.
A good coat of paint helps slow down the rust...

Rigid conduit is second only to stainless steel, which is incredibly rare, so that's about as good as it gets.

What are you trying to accomplish here? Who are you trying to convince it needs replaced?

I'm working maintenance for a production facility and was asked to go out and look at replacing some rusted out piping and disconnects. After further investigation, there were several rusted pipes and disconnects all located on and underneath these cooling towers.. I want to give a long term recommendation for redoing the pipe, but with proper justification. I would really like to find something on cooling towers that specifically points out to not use right conduit.. It's obviously not working!

Well, in my opinion this is something best left to the right person for the job, a licensed electrician.

There are some corrosive environments where galvanized conduit is not appropriate. Then aluminum or SS rigid can be used. It's specific to your particular job.
There is nothing in the electrical code about cooling towers.

I am actually a licensed electrician, I'm just looking for another opinion.. I want to suggest pulling out the rigid and going to plasti bond or stainless steel conduit and stainless steel enclosures, I just need supporting documentation. I am familiar with the NEC and what it specifies for wet locations, but I don't understand why rigid is permitted if it doesn't last and could possibly result in an unexpected outage if the conduit collapsed and shorted out the circuit. In my opinion, it needs to changed, but my opinion doesn't constitute a PO.