Engineering against multiple environments

You always start with CS.
Then you might want to add a lining / cladding / weld overlay of SS 316.
You need to know the velocity of the fluids that are involved, also if erosion is a dominant factor.

DHURJATI SEN
Kolkata, India

In places with high flow (valves and nozzles) go with very high alloys.

If you have any Cl present at that pH and temp there is no place for 300SS anywhere in the system.
The exception would be alloys like 310 in the hot end.
You need a reference for HT corrosion, with sulfidation what I would worry about first.
Start with the ASM publication by G. Lai.
And once you are below 300F I would worry about acid condensation.
If it were just S and N I wouldn't worry much, but with lots of Cl this could be severe.
For the intermediate temps CS (watching out for SSC) is a decent option.
With the stuff in your gas a lining may be needed.
For the lower temp end coatings (paints) may work very well.
For hotter areas it gets more complex.
Start by dividing the system into zones based on temp, flow conditions, and such.

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P.E. Metallurgy, consulting work welcomed

Already use a fiberglass lining alongside high temperature paint for the shell. Going to try a cementation coating for the nozzle itself just concerned that I'm overrating the nozzle external temperature and the cementation coating will just solubilize.

I'm pretty well versed in ASM. Unfortunately no one ever writes about this hell process.

Appreciate the comment!