fusion vs.?

By Lawrence (*****)

Date 03-02-2008 14:23 Edited 03-02-2008 14:26

For Defect #1
What you describe for the first defect sounds to me like the melt-thru on the back of an aluminum butt weld. Sometimes you can see a little line where the faying surfaces came together. Sometimes with poor surface prep or improper technique that line can become an inverted depression.

If you judge that discontinuity to be a lack of fusion (which it sounds like to me) it cannot be ignored.

1. You would be in compliance to reject it outright for failing visual per table 6.1 whether or not it the defect is in the base metal or out of the measured base metal thickness in the reinforcement.

2. you might consider an adaptation to your WPS to encompass rework, but this is a sticky wicket because technically rework occurs after inspection, not before (5.19) or you could try to stretch the meaning of (5.15) post weld cleaning, to cover the removal of excess melt thru, that when removed renders the coupon acceptable.

I don't like either alternative. The discontinuity you describe says there is something wrong that you would certainly not leave on a production piece eh?

Why not have them try again with better focus on surface prep and torch angle, including the root faces, no matter how thin the material. Shears out of adjustment or used for multiple purposes are known to leave ragged edges or gunk on root faces, and just a few swipes with a new file can make a huge difference on melt thru profiles.

For Defect #2...... A piece of filler rod still fused to the test coupon? is that what I'm reading?
I guess you have to decide if you are going to visually inspect the whole weld or just the poriton that is to be sectioned... If it were not lack of fusion or a rod end, but a crater crack, would you accept it just because it was at the end of the coupon and not going to be sectioned?

So my opinion...... If they were production welds I would send them back for repair... But since they are performance qualification welds I would reject and retest for the reasons above.

Al has done a lot more testing than I have.. Would like to see his opinion.

By Tommyjoking (****)

Date 03-03-2008 07:10 Edited 03-03-2008 07:50

Lawrence

Yep you read right ...its not actually a visible piece of rod...but looking at it you know exactly what it is. I bit of filler that went astray...a wart on the toe of the weld. I find it unbelievable that these guys think its ok...but I can be a cowboy myself on coupons...for some reason it always works out for me. WPS allows for NO cleanup, no brushing no nothing...it is verbotten!!!! The other is an AL butt joint and you already know what I am looking at because you have seen it plenty of times. Its not the little line on the backside its the backside pushed out .... Your right there is no way that should go either ....it probably closed up but I see no evidence that a keyhole was carried at all. Your right about prep...I might go in a bit early and see whats going on, small changes can often make big differences or make things fall into place.

THanks for the advice
Tommy

By 803056

Date 03-04-2008 14:49

I might take a different tack on the issue of the melt-through. I would defer to AWS D1.2 (assuming that is the applicable standard) and reference paragraph 4.6.2. In this case clause (8) states "Total weld thickness shall be equal to or greater than the thickness of the base metal, but the weld reinforcement shall not exceed the value listed in Figure 3.2(D) or (E)."

Any reinforcement on the root side that includes a crevise or crease isn't going to affect the static strength of the weld. Any notch can result in a crack if cyclic loading is an issue. If the applicable code is not AWS D1.2 then the appropriate criteria should be applied to the visual evaluation.

That isn't to say I would oppose Lawrence's position for elvaluating in-house welders and workmanship, but as a third party I have to apply the criteria published by the appropriate standard. If the discontinuity isn't addressed by the applicable welding standard, the third party is not in the position nor does he have the authority to make up the criteria to suit his whims.

You on the other hand, as in-house QC/QA, do have the authority to draft acceptance criteria that is at least as stringent as the applicable welding standard. You can and should address all the potential discontinuities in your in-house standards so that the welder and other inspection personnel understand what is acceptable and what is not. Your WPS should also include direction on the methods of cleaning and the extent of cleaning required if it has an influence on the quality of the welds produced. I just finished writing a procedure for a client in Canada that includes a little over a page of instruction on joint preparation, cleaning, and assembly. You are correct if you though it was a WPS for aluminum.

Best regards - Al

By Tommyjoking (****)

Date 03-05-2008 10:29

Thank you AL for replying

Its all for D17.1, the coupons were shot down anyway on a visual criteria, The guy is gonna do some more woodshedding before submitting coupons. I did a little rereading on discontinuities and the definitions and the wps. I think he will do fine, he laid some of the sickest caps I have seen in a long time today. Just some occasional hitches in the roots...he is trying to do his weakest alloy group first. I do agree with Lawrence in the fact that if there is any doubt in the visual criteria there is no point in proceeding with testing..so retest. The prep procedures are very very open ....its really up to the welder..he just has to produce the correct end result. You have a great point that a written set of guidelines should be in place....we have that in our production specs but it is not included in our testing procedures.

Thank you again
Tommy

By 803056

Date 03-05-2008 14:11

Since you are testing to AWS D17.1, the visual acceptance criteria are pretty well defined. I assume you are using Class A as the visual criteria.

Cleaning and preparation is often overlooked with disastrous results. Welders need to be taught the proper methods of preparing the joint and cleaning the joint if good results are expected. Welders do not learn by osmosis alone, they need to be taught the proper means and methods of preparing and cleaning the material for welding.

Carbon steel is very forgiving, i.e., we can weld over light rust, light paint, and other forms of contamination and still get amazingly good looking welds (mechanical properties is another story). However, nonferrous materials and high strength alloys presents a different situation that is not usually properly addressed. The common refrain I hear, "They're welders, and they're expected to know ......"

That attitude is very good for my business. It provides me with a comfortable income when they encounter problems.

Best regards - Al

By jrw159

Date 03-05-2008 14:22

Al is right on the money with joint prep. I have tested many welders who have failed due to improper interpass cleaning. Here is the kicker, on GMAW process no less. One would think that interpass cleaning is not that important when using this process but in actuality it is just as important in GMAW as any other process. There may not be an actual flux to deal with, but there is a residue that can cause complications if not brushed out. Even if it is carbon steel, prepare the joint to a bright shiny surface past the weld area and hit the joint with a wire brush between passes. Not following this practice has caused many a good welder to fail a test, myself included. I learned this from failing a groove test many years ago under the misconception that GMAW left no flux or residual contaminants.