Backing Rings and B31.1

Date 09-10-2005 16:22

I have been doing pipe butt-welding with the TIG process (open root) under B31.1. I am interested in using backing rings and maybe changing the process to stick weld. Other than requalifying the process, does anyone have any comments on this? I have done some experimenting and it seems that the welding time is cut in half, the welds seem flawless when disected, and the ID is perfect as opposed to kind of lumpy (tubulant flow, etc). What about fatigue strength and such? Anyone got any experience with it?

By G.S.Crisi (****)

Date 09-12-2005 14:32

A word of warning. Backing rings should not be put before a flow measuring instrument. They create a turbulence that will alter the reading.
Giovanni S. Crisi
Sao Paulo - Brazil

By Firebird (*)

Date 09-12-2005 14:52

do they tend to make more turbulance than the root pass would in an open root?

By jon20013 (*****)

Date 09-12-2005 15:17

absolutely. Don't use them is very good advice from Giovanni! On the qualification question; there wouldn't be a new qualification required under ASME IX rules. Perhaps you could consider consummable inserts?

By Jim Hughes (***)

Date 09-12-2005 19:05

Mr. Firebird,
i agree with the the other two post's. But I would like to address your comment about the lumpy GTAW root. The root using this process should not be lumpy. You should be able to put a very nice root bead with the GTAW process. You will have alot more challenges with a chill-ring with concern to flow than with the GTAW process.
Good Luck
Jim

By jon20013 (*****)

Date 09-12-2005 19:23

Jim; I couldn't agree more. A "good" GTAW welder can place a GTAW root so that it is just flush and smooth on the insides or with the slightest of smooth internal reinforcement.

By Firebird (*)

Date 09-13-2005 20:21

Yes, thanks. Thank you all for the info. Does anyone happen to know how chill ring welds stack up as far as fatigue strength?

By jon20013 (*****)

Date 09-13-2005 20:47

Without doing calculations, I could probably offer a safe opinion that they are not good in that area either; potential to act as stress risers in the unfused areas.

I once thought I could really speed things up at a plant I was working. I suggested we begin using the gap-o-let spacers for socket welds, only to be informed by one with years more experience than myself (at that time) that I would be setting up a galvanic corrosion couplant when used in the carbon steel systems... at first I scoffed, only to learn that he was right! Easier and quicker doesn't always equal better!