Corrosion of SO2 absorption tubes (at high temperatures)

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Hello, everyone! My factory has a salt production process; in the absorption stage, the SO2 generated is drawn out by fans, cooled in a cooling tank, and then reacted with sodium bicarbonate. The biggest problem now is that heat exchange with external water takes place in the cooling tank through four 250mm pipes that wind back and forth. At first, the 250 model used carbon steel material, 12mm thick. It’s been in use for over half a year. Due to immature manufacturing processes, the process was halted many times back and forth; it is suspected that SO2 combines with water after condensation to form acid, which corrodes the pipes. In May of this year, it was replaced with 316L material (6mm thick), and production was also halted a few times in between. It becomes corrosive in September. In the past two days, it corroded through again. I’d like to gather some ideas – could you advise me on what materials can maintain their corrosion resistance at high temperatures of 800~900°? Thank you!