I need a metal that is a strong thermal conductor, resistant to acidic/caustics, and is fairly inexpensive?

I am looking into a way to cool down a production oil tank so its temperature fall in to a acceptable range in order to send it down a pipeline. I am planning on welding various cooling fins in through the side of the tank hoping it will transfer the thermal energy out of the tank and dissipate it to atmosphere. (the tank is insulated). In order to break up emulsions we must heat the oil sometimes in excess of 65 C, our max temperature for the pipeline is 40 C, i need this temperature drop to happen as fast as possible. The P.H. in the tank can range from approx. 4-11, generally a phosphoric acid and alkaline caustics. Please sight sources.