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Up Topic Welding Industry / Inspection & Qualification / double groove
- - By doyenofcastle (**) Date 09-28-2008 14:49
when we make back gouge and grinding for the other side of double groove :
how you know you reach to the sound metal and all weld bead is ready for welding
if  you see linear indication how to use etch to tell you  whether it is a grinding mark or this edge of the root face
Parent - - By aevald (*****) Date 09-28-2008 17:02
Hello doyenofcastle, I believe you could possibly use mag/particle testing or dye/penetrant testing to show if you have gotten to sound metal before proceeding to do the weld-out. These would probably be two of the easiest and possibly the most economical ways to approach your question. If you are speaking of how to use the dye/penetrant, it is a two-part process, first you spray on the dye, then you spray on the developer. If you have any bleed through of the dye, those spots will be where there are indications for cracks, holes, or other weld defects. My $.02. Best regards, aevald
Parent - - By jrw159 (*****) Date 09-29-2008 14:25
Aevald,
  Very good suggestions. However, liquid penetrant testing is a three part process. The area must be thoroughly cleaned prior to the application of the dye. The cleaning step is more important than many give it credit for, as if the area is not cleaned properly, false indications can result. FWIW

jrw159
Parent - By aevald (*****) Date 09-29-2008 14:49
Hello John, as everyone has responded with various points of logic, not necessarily a simple answer and everyone has valid reasoning for their stance. Type of service would likely also influence the degree of use and justification for how far to take the inspection aspects of ruling out discontinuities. I appreciate your additional information on PT as I over-simplified it. Hope the original question has been answered to the poster's satisfaction. As usual, I have learned and I'm sure that others have too. Best regards, Allan
Parent - - By js55 (*****) Date 09-29-2008 12:51
I think the simple asnwer is, you can see it. You can actually see the line being 'eaten' up so to speak as you move the gouging rod along the weld. If you then grind to clean metal (as most codes require) you should easily be able to visually determine if you have ground far enough. The only time I would use additional NDE would be if I suspected cracking.
If you're doing a lot of this you don't want to to spend so much time with MT/PT.
Parent - By CWI555 (*****) Date 09-29-2008 13:42
Finding LOF or cracking at the root is not so easy to visually determine. Especially at the inherent viewing angles of a backgouge (depending on depth of preperation).
Parent - - By ctacker (****) Date 09-29-2008 13:52
Quite a few of our welds require MT of a backgouge. you'd be surprised how much gets missed!
Parent - - By pipewelder_1999 (****) Date 09-29-2008 14:30
On a cleanly backgounged joint that has not yet been ground visual inspection can work pretty well however because the quality of gouging that I have seen often varies a great deal, MT or PT is nice. I like PT because I can do more feet in a given amount of time and there is a better visual indication for the welder.

The variable is the quality of the gouge. Its my experience that when I carbon arc gouge a weld from the back side, when its viisually clean, it passes MT/PT.

One thing that causes problems is not the IP being removed but non fusion along bevel faces. I have seen the two lines widen and grow farther apart as you gouged deeper. These are sometimes easily missed when back gouging.

Gerald
Parent - - By ctacker (****) Date 09-29-2008 14:52

>The variable is the quality of the gouge. Its my experience that when I carbon arc gouge a weld from the back side, when its viisually clean, it passes MT/PT.


your right, more times than not they would pass, But it also depends on what your backgouging. When your going into a 4"-8"groove 2" wide acting like a contortionist 15-20 feet in the air then sometimes its hard to see as your gouging. if you cut a straight line thats easy to see, you shouldn't have a problem, but its not 100% you always get everything out!

Regards, Carl
Parent - - By pipewelder_1999 (****) Date 09-29-2008 15:06
I do agree a large area of gouging is better inspected by some process that covers a large area with consistant results. VT is not one of those for sure.

I just dont want anyone to thing that Arc gouging in and of itself "Masks" anything. In my opinion it will reveal indications that are not visible when grinding alone.
Parent - By kipman (***) Date 09-30-2008 12:42
I fully agree with Gerald on this.  The only thing I would add is that when working with non-ferrous materials some are a bit softer and like to smear when grinding (Monel comes to mind) and in my experience it is often difficult to determine if you've got a good backgouge with only VT.
Mankenberg
Parent - - By Mikeqc1 (****) Date 09-29-2008 14:11
Mt would do just fine an indication open to the surface  would be a sharp well defined particle build up near the center and  a subsurface indication would be a broad fuzzy indication , Pt would also work but may not pick up some areas that smearing may have occurred.
Grinding marks IMO are usually curled like this (  in other words they follow the spin of the grinding wheel .If you have a linear indication that curles and holds very little Dye you could lightly grind again and reapply the PT if it disappears your ok if not then it may need more evaluation.
The root in either method should jump right out at you.
We use both methods PT and MT and you'll find a lot more using these then just doing a visual.
MDK
Parent - - By js55 (*****) Date 09-29-2008 17:17
I think we're confusing the question here. The question was, "how do you know when you reached sound metal?"
You don't need MT/PT for that.
I would submit that if you've found due concern for using MT/PT on backgouges you might wanna consider the more effective means of questioning the abilities of your welders and gougers.
And if you have cracking and fusion problems you might wanna consider not waiting for a backgouge to do NDE. I would submit UT would be a better resource.
And before we disparage VT too much, let's keep in mind that almost the entirety of D1.1 is based upon VT.
Parent - - By ctacker (****) Date 09-29-2008 17:31

>I would submit that if you've found due concern for using MT/PT on backgouges you might wanna consider the more effective means of questioning the abilities of your welders and gougers.


Maybe we should change the job specs to say "If a qualified welder and gouger arcs a root, no further testing is needed. :)
we test joints that the job specs call for, every now and then a welder will ask for a MT of a root for his and the company's own good!
when you fill a 8" double groove, backgouging the root, you want to be damn sure the root is sound before filling it up and finding out through UT that your root is bad!
Parent - - By js55 (*****) Date 09-29-2008 18:24
Wouldn't you wanna make sure the whole damn thing is sound before filling it up further. Not just the root? Or is grinding (or gouging) down 3 1/2" acceptable though 4" isn't?  :)
Can't the same logic justify progressive mags? Is LOF above the root better? And if I were to advocate progressive mags, would you then tell me I was too conservative? Or are you performing progressive mags? Is everybody?
I don't think we're in as much disagreement as it may appear. Its a good discussion.
Parent - By ctacker (****) Date 09-30-2008 04:55
If the specs call for progressive , then we would do it.
The root is the most problematic part of a weld (IMO). If you don't get backgouge to sound metal, you could have a crack propagate through the whole weld, especially on AR plate.
Could be the engineers know a welder qualifies by a test plate, but there is nothing in the code about having to qualify Carbon arc. so could be they want that to be extra insurance of hitting sound metal.

you do have a good point, but when specs call for one thing, and you need a paper trail, you gotta do what you gotta do!
Parent - - By Mikeqc1 (****) Date 09-29-2008 17:54 Edited 09-29-2008 18:10
i always do a visual before any Mt or PT tests and sometimes i see the dicontinuity and sometimes i dont, but With an MT or PT test I will see indications that i didnot see on just a visual.
I have questioned mt on deep grooves and the strength of the magnetic field at the root.
MDK
Parent - - By 3.2 Inspector (***) Date 09-29-2008 18:21
Great and correct reply IMO

3.2
Parent - - By hogan (****) Date 09-29-2008 18:48
As far as AWS is concerned, MT and PT are only visual enhancements. To aid in the detection of discontinuities open to the surface.
Parent - - By 3.2 Inspector (***) Date 09-29-2008 18:58
Yes.
May I ask why you mention that in this context?

3.2
Parent - - By hogan (****) Date 09-29-2008 19:33
no
Parent - - By 3.2 Inspector (***) Date 09-29-2008 19:39
ok, I wont
Parent - - By hogan (****) Date 09-29-2008 20:02
thank you
Parent - - By mountainman (***) Date 09-29-2008 21:33
lol
Parent - - By Joey (***) Date 09-30-2008 14:01
No objection on "use mag/particle testing or dye/penetrant testing to show if you have gotten to sound metal before proceeding to do the weld-out"

however, will you allow your welder during performance qualification test to use MT/PT when he is being qualfied on test plate with back grinding and welding?

Best regards
Joey
Parent - - By js55 (*****) Date 09-30-2008 14:23
I'm still reading arguments that justify looking for discontinuities such as cracks or LOF. But I've heard no argument that justifies thinking in terms of difficulty in determining good sound metal. Essentially, if its shinin, its good sound metal. The carburized layer is the problem when backgouging with air arc, oxidized layer with plasma. If its shinin the carburized/oxidized layer is gone. If you have concerns for cracking or fusion or whatever, thats certainly valid. And would justify additional NDE. But it is not a concern for good sound metal when considering the context of the requirement for grinding backgouges. Lets not confuse the issue here.
Parent - - By hogan (****) Date 09-30-2008 14:53
js55,
There have been many times when I was performing MT of a back gouge, when no lack of fusion (lof) was visible. Yet when the MT is performed the lof is there. This is more common when the metal is shinny. Like if a back gouge was cleaned out with a die grinder. You can have a instance when, after back gouge, and cleaning with a die grinder the excavation is clean but there is still tight lof. It can not be seen with the naked eye but is evident with MT.
Parent - - By aevald (*****) Date 09-30-2008 18:52
Hello hogan, one of the nice things with grinding a lot of the time, is that the grinder dust acts simlar to MT. In many instances I have ground out cracks and the residual magnetism contained in the part itself along with the grinding dust, will leave nice indications of remaining cracks. Not quite as technically correct as using the "real" equipment for this sort of testing but a decent indicator in many cases anyway. Just figured that I would throw that into the mix here....for what it's worth. Best regards, Allan
Parent - - By mountainman (***) Date 09-30-2008 19:24
Allan, i too have encountered that.

JJ
Parent - - By Mikeqc1 (****) Date 09-30-2008 19:26
i THINK THATS HOW THE METHOD WAS DISCOVERED.
Parent - By kipman (***) Date 09-30-2008 22:33
It was discovered in a similar way.  Carl Betz, a machinist.  He noticed fine machining particles sticking to cracks on tool steel that he was machining.  He figured it all out and started Magnaflux way back when.  Smart guy, saw an opportunity and grabbed it by the short & curlies.
Mankenberg
Up Topic Welding Industry / Inspection & Qualification / double groove

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