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Lawrence,
I understand that not everything is required to be manufactured to a code or standard, and to be quite honest there is more than I would have ever imagined that is not.
Also it is not just your region that has these growing pains. Some regions may be a little more acustomed and used to it. You almost can not sell a gumball machine to a customer without some referance to code if there is any welding to be done now days.
Please permit me to ask another question.
Is there an increment referanced for the removal of the substances listed in 4.11.1?
John
Hey John,
I don't see any incramental measure for oxide removal... However there is substantial text (too much to type) devoted to plasma cut edges and cut quality. (4.11.3 and 4.11.4)
lawrence,
Thank you for taking the time to enlighten me.
From the information given it would appear that removal of the coating from "The weld area" is indeed a code requirement.
However, as you have stated, code is not always required by customers.
As always, I take great satisfaction in reading your reply's and comments.
Best regards,
John
The problem I have with this is that I am not completely convinced that it does work. Yes it may work for this particular application, but what about an application that may see more severe stresses. That is why I'ld like to hear someone come out and say that they have successfully and consistently qualified procedures welding this way. I am not saying that it cannot work, I would just like to see more testing that proves it is a sound method.
I'm with you!
Would very much like to talk to somebody with first hand experience with running PQR's on welding annodized Alum with GTAW and zero surface prep.
This makes three of us.
While this is not my "field" so to speak, I am always interested in welding on "coated" material of any kind.
John
The July/07 issue of the welding journal has an article in the research supplement about GTAW on 5083 anodized aluminum. A quote from the abstract "...weld bead dimensions, notably penetration and bead width, increase with the percentage of electrode positive polarity during the unbalanced square wave AC welding of Al alloys with the GTAW process. This is in direct contradiction of conventional assumptions about the role of EP and EN contributions to surface cleaning and fusion behavior during AC welding." They did various autogenous BOP welds with varying amount of anodizing thickness. "When up to 70% EP waveforms are used, thicker surface oxides enhance penetration and (to a lesser extent) weld width, but restrict sputtered width{ the etching at the toes}. Thick oxides produced by anodizing are more difficult to disrupt. This resilience restricts the area of arc impingement and increases the energy density forming the weld pool at a given arc power." In their conclusions they state "Oxidized surface layers enhance fusion volume and penetration." Nowhere in the article do they mention anything about weld strength, but this certainly makes you wonder.....
There was a session at the welding Expo about 10 years ago from a Canadian Professor that provided evidence that penetration was deeper with EP balenced AC GTA welds.... It flew in the face of common assumptions but he had plenty of hard data and PQR material to back the claim...
If there is more oxide removed it makes some sense that this would allow for more arc energy to go deeper into the pool... Less energy reflecting off of oxides I suppose.
I have always remenbered that session and it is one of the reasons I don't particularly favor the high bias toward EN that the manufacturers of inverters often suggest is superior.. My favored practice is to use as much EP as possible without distorting my electrode tip, and to use frequency control (when available) when it is necessary to reduce profile sizes in fillets.
There are many other factors to consider also. I don't think blanket statments redily apply here. Penetration profiles with a specific balence setting may be different in a fillet than it would be with a bead on plate... The wide puddle profile that is excellent for a surfacing weld or a saddle, might tend to bridge across a tight fillet.
Bias toward EP also effects electrode size, tip prep and ability to weld out of position.
For the benifit of those who havn't seen a tuna tower up close, the weld fillets are rather large for the thickness of the tube. I suspect the reason is that the weld may have some poriosity and oxide inclusions, but there is enough sound deposit that strength is not an issue.
I figured this was you Spencer.
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