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Why does the acceptable criteria for bend tests not mention cluster porosity?
This is for a welder qualification. Mild steel to mild steel, 7018 rod. Passing the visual and then porosity shows up after the specimen is bent.
Did the porosity result in a crack? Was the crack large enough to fail the coupon?
No, then the porosity is not a concern.
Firstly, thank you both for answering my question. I just want to say that I find it facinating that a bend test may open up several tiny holes of porosity and pass. I would have thought there would be some kind of limitation on how many you could have for a given area on the coupon.
They do Louis; any open discontinuity measuring more than 1/8-inch is a reject or if the sum of the open defects measures more than 3/8-inch, the coupon fails.
Remember, there ain't no such thing as a perfect weld. The question is, whether the weld is "good enough."
Only other thing would be if any of pores were over 1/8", or if there were enough pores larger than 1/32" that added up past the 3/8" limit.
All indications were smaller than 1/32" so they don't count. I did sand and etch the bend on the edges and found even more porosity. So it ran throughout the weld which in my non-welding engineer opinion should fail it, but not according to D1.1. You have to remember to keep your opinions out of the decision. That's why I posted, so I could get the facts from someone more up to date and knowledgeable about D1.1 than myself. Thank you all again. Great forum, with very knowledgable helpful people.
Louis I think you are mixing inspection criteria.
Table 6.1 speaks to porosity and sizing of porosity. But table 6.1 does not apply to guided bend sample inspections.
18.104.22.168 Acceptance Criteria for Bend Tests. is what must be used when straps have been bent. "Discontinuity" is the term used for everything you might see on that "convex surface" of the bend strap. Meaning, Porosity of any size, slag inclusion, crack, anything,,, It's all a "discontinuity" and shall be measured within the criteria limits provided.
For example.... If there were some little pores before the straps were bent, but after bending they became linked by cracks, the entire length now must be measured. Or... If the bending stretched the pores and made them larger, that change in length must be measured and added up to see if compliance is done.
In essence all indications (discontinuities) count.
The edges don't count... Only the "convex surface" of the strap is to be inspected.... So the sides or the back can have cracks or porosity or anything else and it is meaningless... It took me a long time to swallow this fact I can assure you. But it is what it is.
Also... Think about this.... You can sometimes see a strap that has porosity do a bend 180 degrees and it doesn't snap, doesn't tear, and the pores don't even elongate much.... What this really says is that *sometimes* porosity is not that bad... If a weld can bend 180 degrees with it and nothing bad happens... Why do you want to fail it eh?
The standard bend diameter for steels with a YS of less than 50 ksi produces a 20% elongation on the convex surface. That is pretty good amount of stretching! If the sample doesn't exhibit any unacceptable open defects with that amount of elongation, it has to be a pretty decent weld.
I know on the visual there is porosity criteria given in D1.1 and I did not find any such criteria for the bent stap or coupon as I call them. This porosity was not visible before it was bent. There is a pretty good picture I posted of the coupon on my Instagram account, @price_welds if you want to see it. It is at the top as I just recently posted it. With reguards to the bend criteria, the way I interpret the code is that any discontinuity smaller than 1/32" is not counted towards failure. (If on the convex surface of a bent strap there are discontinuities that measure less than 1/32" a piece, but they all add up to be greater than 3/8" it passes. - Same scenario, but now the discontinuities are all at least 1/32" in size and add up to be greater than 3/8", it fails, are these two statements correct?) I want to fail the first scenario, but I don't because D1.1 does not. You guys are right that the porosity does not mean it will fail, but its appearance does not foster a lot of confidence in the weld either. I don't want to "know" that the welds holding up the bridge I'm driving over have this kind of porosity in them. Which brings me to ask, if there is criteria for the acceptable amount of porosity in a visual inspection of any weld, why is there not the same criteria applied to a bent coupon? Again as I stated before, I am not a welding engineer nor any other kind of engineer, I'm just a welder/former CWI/ welding teacher. Thanks again guys. You are helping me learn.
Well my friend, if it will help you sleep at night, D1.1 isn’t used on bridges :)
If the total of The discontinuities add up to greater than 3/8. Fail the strap... keeping in mind the note on corner cracks.
Lol, thanks Lawrence. I feel better already
D1.1 is pretty specific on the type of porosity it considers to be "harmful" to the weld. The visual criteria only addresses "piping porosity". There is no criteria for other types, so in the case of a production weld, other forms of porosity is not considered during the visual examination.
When you think about it, what is a bolt hole in a structural member? It a big pore hole that is round, extends through the thickness of the member, has sharp corners, and represents a significant loss of base metal. Granted, the loss in cross section must be factored in when doing the calculations, but really, is a small amount of porosity any more detrimental than a small drilled hole? After all, the porosity represents a small loss of cross section and is usually spherical or at least rounded.
Haha, you guys are killing me..one hole in my member is all I'm allowing...
Thanks again for the replies. I feel a lot more confident passing stuff now....
Just to address your bolded sentences:
You only add up discontinuities that are greater the 1/32" and less than 1/8", total over 3/8" it is rejected. If the discontinuities are 1/32" or less, you don't even count them nor add them.
"When welding arc spot welds, what decrease in welding current(amperage), wire feed speed or melting rate is permitted, without using another WPS?
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