Pressure Vessel Materials

Do you mean to use different material in the same vessel???

Did you consider that the material selection might be something that is determined by the process parameters? Corrosion might be an issue.

Yes, but it helps if the materials are not too far different, such as in unlike p-groups.

First define shell and head. If you define the shell as the main body of the vessel and the head as one of the end sections, then the answer is clear: why would you want to? If by shell you mean a jacket around the vessel to accommodate heating or cooling via steam or chilled water, then you would be limited by how well the materials would adhere in a weld, and the longevity of the bond, taking into account the differences in thermal expansion of the two materials.

Have you checked the ASME code?

Have you checked the ASME code?
Ouch! Seen that coming!

Yes, but weldablity must be considered. Just do the math. I would not suggest something like A36 but more like A516-70. For the slight increase in cost the assembly is cheaper as thinner gage can be used.

Never mix paper and plastic.

Yes, provided the weldability compatibility. Note that the shell is usually ROLLED steel, and heads are normally FORGED. Check ASME Section II-Materials.

The process materials might be the determining factor, together with temperature and pressure. A snare drum, for example, fits the description though the process material is only air at ambient conditions. So the nature of the process is the determining factor.

Consult a Process Engineer locally.