technical

Date 06-12-2014 14:51

Hello moontan002, the short answer to your question might include a couple of items: you may see silica islands(glassy type of material) due to type of filler used and make-up of parent metal, you will also likely see a scaly gray type of surface condition covering and extending out from the root penetration or sucked-back portion of the root and on both sides of that region(oxides formed from un-protected weld metal or metal that has exceeded the reactive temperature of the metal). You could use a purge-gas backing to get rid of some of this, however in most cases this is unnecessary and cost prohibitive. You could even use Solar Flux to help limit this sort of condition, although Solar Flux is generally used on stainless steel as a less expensive way to protect the backside of a weld. Can you include more information and maybe pictures to describe your situation and why you are particularly concerned with the backside condition of the weld? Good luck and best regards, Allan

By Chris2626 (***)

Date 06-12-2014 17:51

i've gotten this as well I was taking a test that was going to be x-rayed and i had this scale on the inside on the root. I actually took a plumbers brush and cleaned it off in fear that it may mess up the x-ray. The Inspector when he looked at the root asked if i had purged it and i did NOT but it looked like it because I cleaned the sale off. I made the x-ray without a problem.
Friend told me it was good i cleaned the scale off the root because it may have not passed x-ray but not sure if that was true or not. If you are in doubt when you do your test just run a plumbers brush inside that is if it is a small 2 inch pipe clean the scale off to be sure it passes.

By Metarinka (****)

Date 06-12-2014 18:16

What you are seeing is oxides and slag from an unprotected root. it can be prevented by shielding the backside with an inert gas, using solar flux or similar, or using a backing. Alternatively it can be ground out.

A weld needs to be properly shielded on all sides during welding, open roots require shielding or you will get excessive oxides and scale build up that can affect mechanical properties.

By Superflux (****)

Date 06-12-2014 20:44 Edited 06-12-2014 20:47

The oxide scales and "glass" (silica islands) on the root side are of much lesser density than steel and will not show up on an X-ray. Since they are on the surface, these are also "invisible" to UT.
For the vast majority of low allow/mild steel work, it is an irrelevant issue. If it were, then back purge would have been required.
I recommend leaving it in place. You never know when you might, in your over zealousness of cleanliness, uncover something that some sphincter inspector could see and shoot you down on a visual.

By ssbn727 (*****)

Date 06-13-2014 05:01

Excellent explanation John!

I lost track of how many 2", 4" & 6" GTAW roots I passed over the years but I will say this,not one of them did I reach in to clean off the oxide scales & silicon islands and almost everyone of those passed RT or UT no problem... The very few that did fail did so because of other factors like slag inclusions, or a cracks, etc... And if I could count how many failures I had while qualifying with the fingers on my left hand (Southpaw), it would be less than 5...

Btw, I have a few knifemaking and blacksmithing books in .pdf and I've been meaning to get in touch with you about them... PM me your e-mail address so I can send you them.

Respectfully,
Henry

By pipewelder_1999 (****)

Date 06-13-2014 10:25

Superflux,
Excellent point and explanation. I think many often think that radiography "Picks Up something in the Weld" however its more in tune with finding areas where things are missing.

An interesting point to mention is that root oxidation is not listed as a discontinuity in many codes (which many may already know). And I do understand the situations in which it needs to be controlled. Which reinforces my belief that "Code Compliance" is not a suitable replacement for Engineering and QA/QC programs.

Have a great day
Gerald Austin

By moontan002 (*)

Date 06-16-2014 14:11

thank you for all your responses

By Stringer (***)

Date 06-18-2014 01:27

Could be my imagination but I feel the 'copperless' version of ER 70s-2 Inweld seems to produce fewer silicon islands. This is such a dumb post. I should do a simple A/B test before I post such a subjective opinion on something that is measurable.