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Up Topic American Welding Society Services / Certifications / Removed The Backing Strip and a Little Bit More..
- - By tom cooper (**) Date 07-16-2007 15:10
This might fall into the "trivial" category, but then again maybe not - need your advice!
After welding up three welding coupons (3/8-inch plates) we sent the plates down for removal of the backing strips. In so doing, the machinist took off about .030-.035" off the entire back surface.  Does this negate my PQR? or may I just derate the thickness limitation for the WPS? 

In looking at the Transverse bend test and Tensile test speciman dimensions in AWS B4.0, it appears that some surface removal should not affect end results since the testing lab will use actual cross section dimensions for calculations.

Thoughts? Advice?

Parent - - By jon20013 (*****) Date 07-16-2007 15:59
Depends on the Code your working with I guess.  I know for ASME work it's not a problem.  I once had nearly 1/4" extra removed in a similar situation and WPS / PQR required Customer approval prior to use.  I had "derated" the thickness of the WPS voluntarily but Customers Welding Engineer (a very, very sharp guy) told me to keep my original thickness (as it was the thickness of weld deposited) and simply make a note that the thickness was reduced to facilitate undersized tensile specimens.  The PQR and WPS flew through all review cycles.  Good luck, I wouldn't think the small amount removed should pose too much difficulty but I've been known to be wrong before! ;-)
Parent - By js55 (*****) Date 07-16-2007 16:54
30 to 35 thousanths in machine world is a lot. You might wanna take that machinist out and smack him around a bit for fallin asleep. Just kiddin.
Jon is right. If ASME, it doesn't present a problem to my knowledge. Your tensiles are gonna be reduced section anyway. So, by the time you machine grips and the reduced section from your rough cuts the material you are talking about won't be there anyhow (even more so if you use rounds). Just record it in the notes so all is honest.
Parent - - By bozaktwo1 (***) Date 07-16-2007 17:00
Just one thought: So the machining operation removed part of the root?  What bends are required for your PQR?  I am only thinking of the side bends I have witnessed.  Let us know how it turns out, please!
Parent - - By tom cooper (**) Date 07-16-2007 20:06 Edited 07-16-2007 20:12
Bozak21-
That is right, part of the root was taken off.  I have to do two root bends and two face bends. As well as two tensiles.   As it turns out, we got quite a few linear indications in one of the three plates (all indications inline with the weld) and so we are going to redo this weld before we send up to heat treat and then out for Lab testing. We can't explain why the second plate came up with these indications!  MT inspection of Plates #1 and #3 were flawless.

Which brings up another question - Under ASME or even AWS rules, is surface grinding permissible to remove minor flaws during a PQR?   In other words, if grinding off an excess of material, say the .035", while removing the backer was not objectionable, why then can we not remove some surface material for the purpose of removing minor linear indications?  It is possible that taking .065"-.075" off the surface might eliminate most or all these linears that we found.   I quess it is "intent" that I am questioning.
Parent - - By js55 (*****) Date 07-16-2007 20:45
This is an interesting question and really goes to the root of a major difference between ASME and AWS. IMO, ASME takes the idea of tensiles and bends literally, I suppose is a way to put it. In other words, you are verifying mechanical viability. Strength and ductility. It is assumed that the material will be free of flaws. Flaws are implicity segregated to welder ability. In other words, if your welder is putting slag into your PQR coupon shame on you.
AWS don't see it that way and mixes in performance variables with procedure variables.
Now, IMO, its not quite as clean as either approach would emphasize, since running too low of amps could clearly cause slag no matter how good your welder is. But even though AWS has some justification, which may be related to a concern for prequal thinking, (just guessing here) I do think the ASME approach is closer to reality. Welder incompetence should not be an issue for procedure qualification.
So in your case, think aobut it, evne with bends some material is coming off. you don't want to bend a rough cut. So, IMO, its a question of how much your removing. And how deep your flaws are.
Parent - - By jon20013 (*****) Date 07-16-2007 20:47
EXTREMELY well said js55!
Parent - - By tom cooper (**) Date 07-17-2007 09:13
Agreed! thought provoking and very well stated.
A next natural question is:  Does ASME Section 9 prohibit repair of welds in the PQR phase? If the philosophy is that a PQR is a trial of the mechanical viability of the weld joint, and we observe a workmanship related flaw prior to the destructive testing (slag inclusion or minor linears, even porosity) are we allowed to repair the coupon?  I read through Section 9 last night and didn't see any language which would permit or prohibit this.  Where/how does D1.1 specifically address this question?
Parent - - By jon20013 (*****) Date 07-17-2007 11:39
Tom, in my opinion and experience, there's nothing to prohibit repairs prior to testing in fact I would expect that repairs would be accomplished in my own shop if defective conditions were noted on a coupon.  Got to remember, its not about workmanship but mechanical soundness, the weld has to be sound at the time of testing.
Parent - - By js55 (*****) Date 07-17-2007 14:00
Tom,
In addressing your question I would say that if you wrote to Section IX for an interpretation you would get an answer very similar to your own. Just my opinion. It simply doesn't address the issue. So you fall back on "Sound Engineering Judgment". This is NOT an oversight on they're part.
Too many people look at the codes as a cook book, and therefore take the approach that if it doesn't specifically discuss or allow it, it is prohibited. This is the exact opposite of code intent.
If the code is silent then you have to rely on your SEJ. And this also means that nobody has code justification for rejection as well.
And if the code is silent on an issue I can pertneer garowntee the answer will be "The code does not address that issue" or some such language. A response that even a cursory review of code interpretation will reveal as the most common response.
Parent - - By tom cooper (**) Date 07-17-2007 14:38
You know, this simple question I originally asked is causing me to take on some new points of view. Although I view the Code as more of a "law book" rather than a cook book, I do forget that it leaves room for, and often times requires, the SEJ factor.

More importantly - info, interpretations and experience shared and posted by unselfish folks as yourselves gives us other guys confidence to apply that SEJ and defend that judgement when the Code police arrive.

Thanks fella's, all very much appreciated.
VR
Tom
Parent - By js55 (*****) Date 07-17-2007 15:45
Tom,
Everybody in here has something to give, and something to learn.
Up Topic American Welding Society Services / Certifications / Removed The Backing Strip and a Little Bit More..

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