The lower content of elements nickel and molybdenum in the alloy used to manufacture these pipes in comparison to the conventionally utilized austenitic grades with similar corrosion resistance properties, gives the alloy grade 2205 Duplex Steel Pipe a lower cost. And since Duplex grade 2205 stainless steel is about two times as strong, it results in material savings because the wall thickness requirements can then be reduced. Which would mean that less metal has been consumed during production therefore a lower cost component has been achieved. In comparison to ferritic grades, alloy grades for duplex stainless steel is much more tougher than ferritic stainless steels.
While considering alloy grade 2205 duplex stainless steel pipe for Heat Exchangers, more often than not proves to be beneficial for these applications. This is because the content of lower nickel in the alloy grade 2205 Duplex Steel Pipe means a better thermal conductivity in comparison to its austenitic equivalent grade. Therefore there is Less heat transfer surface area required to perform the same task.
You can find more information about the price of Stainless Steel grades such as the Duplex 2205 Pipe in the link given here.