The Chlorine Institute puts out a manual that will be of some help on this. Also, is there any O2 or water in the system? Chlorine is an extreme accelerator for oxidation at high temps. I'd also check out the Haynes site. We looked at Haynes 556 alloy for a high temp chlorine/O2 environment used to regenerate dehydrogenation catalyst. They have an on line technical support that was very helpful.