Thank's guy's! Yes, js55, hardness is off paramount importantance which is why we have a very high preheat, followed by mandatory bake-out (which, reduces a few of my worries) and then, naturally the PWHT. All-in-all, the specs are written ultra conservative but I've no idea's why this alloy was selected as the optimal for this service either and yes, the -36C is considered our design ambient, not the service temperature. I spoke with Bill some months back and he really simplified things for me, I'm just second guessing some of my own thoughts! I appreciate any further input.