Opinions? purging for GTAW roots; SA-182, F22 Mod. sour svc?

Date 02-08-2008 13:02

Hi Jon,

I'm with you on what my recommendation would be; simply because the codes don't require it. However, all of our high end clients (Petro - Chem big dogs) who have solid engineering departments that include welding engineers; require back purging. It makes things simple for us.

Charles.

By js55

Date 02-08-2008 14:52

jon,
Let me exhibit my ignorance here and ask a question.
When you say -36 are you actually talking ambient or service. You're talking ambient aren't you(Kazakhstan?)? It seems strange to me that the choice of alloy for such low temps would be an alloy that was originally designed for high temp creep service, using metallic alloy additions (W-Nb-V-similar to Grade 91) to increase creep strength while reducing carbon and minimizing cold cracking.
The problem with no purge of course would be surface oxides. And would these surface oxides contribute to accelerated corrosion under sour service? I don't know.
But (and keep in mind I'm just brain stormin here becasuse its been along time since I've dealt with these alloys) if your cookin any of this stuff your gonna have surface oxides as well. And mild carburization and sulphidation if you use flame furnaces. I would think that reducing hardness would be a greater issue than surface oxides.
EPRI did a lot of work with these alloys since they were orginally intended for power applications, you might give Bill a call. He keeps in close touch with the guys at the Charlotte office of EPRI. There are boxcars full of papers on this alloy. There should be something of purging. If you find them let me know. Once I wade my way through the stuff Henry has posted I won't have anything ro read.
Or you may google Sumitomo and Mitsubishi Heavy Industries. They did the early work on these alloys if memory serves.
The DOE website may have something too. I'll check that for you. I have that one in my favorites.

By jon20013 (*****)

Date 02-09-2008 00:05

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.