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Up Topic Welding Industry / General Welding Discussion / Aluminum Pipe Groove Welds
- - By swsweld (****) Date 03-10-2015 18:33
We'll be doing a repair on a 2" .218" WT open root 6061 Al with ER4043  wire using GTAW process in the 2G position. The groove angle is 60-70 degrees, root opening 1/8", back purge and torch gas with argon.

Any advice on best practices for tungsten type and prep, material prep and technique are welcome. I'm not an expert on Al. welding but do have some knowledge and experience although it's been a while. I've only used pure tungsten with a ball tip but I've been told better choices are available. Is acetone the best solvent? Acetone 1st then mechanically clean or grind then use acetone? What is the best finish before welding...file? Grinding and power wire brushing (SS) can, IMO, smear over and and leave contaminents that will affect the weld causing porosity. I would think a slightly larger gap and groove angle would be helpful. Is the keyhole method best for this application? Gas lens or standard lens. How much tungsten stick out? Large cup or small? 1/8" or 3/32" tungsten?

My Al. welding experience is limited to misc. metals and structural shapes, not groove welds on pipe.

The weld will be RT'd to ASME Sect. VIII also so any solid tips are appreciated.
Parent - - By aevald (*****) Date 03-10-2015 19:00 Edited 03-10-2015 21:51
Hello swsweld, you may not need the back-purge. I am saying that because the back-purge will likely not help much with fusion issues and oxides that are so common on the backside of an aluminum open-root welding scenario.

The DCEP portion of the AC current is the cleaning factor and unless there is a direct application of this current to the backside of the weld groove there will be fusion line issues and oxidation indications on the inside of the pipe.

Wire application methods on aluminum are important: you will not use a lay-wire technique because of two basic concerns: the wire blocks the cleaning action of the actual electric arc that is DCEP and the 2nd factor relates to "debris" or other undesirable contaminants that, having the rod cover over the top of, will prevent removal or dispelling of them because they are not in the direct path and contact with the DCEP component of the arc. 

As wild as this may sound, you might consider having your welders, or yourself, employ a back-hand progression and a relatively steep drag angle and keep the tungsten down deep in the groove with a viewable key-hole and feed wire in behind the tungsten just above/in front of the puddle edge. Dabbing with a near vertical rod angle and keeping the rod end in the shielding envelope as you move along. A #12 gas lens wouldn't be a bad idea either. A feather edge prep may be beneficial with this method although this also opens up the keyhole and requires more filler metal and longer weld-out time.

Whether you consider this method or not, get some pieces to practice on first. I am pretty sure that this is already going to be the approach of yours. Please keep us apprised of your progress and challenges. Good luck and best regards, Allan
Parent - - By swsweld (****) Date 03-11-2015 23:30
Allan, thank you for the helpful info. That is an interesting technique that you mentioned. One welder did a square butt and got full penetration but had lots of porosity in the RT. It also had a visible lack of fusion line on the root ID. It was easily removed with light grinding. Not sure if we'll be able to access the ID on site or not. I do wish that we'd have time to run a few with your mentioned technique but time won't allow it this late in the game.  We had lots of tungsten inclusion with the pure tungsten on a standard open butt weld and I'm not sure if it was technique, the pure tungsten or perhaps the machine as we were experiencing inconsistencies with it. I've always used pure tungsten on Al but not opposed to trying 2% thoriated or other.
Parent - - By aevald (*****) Date 03-12-2015 00:58
Hello swsweld, try using the Ceriated tungsten, we use it because it is a good all-around choice. It will also hold it's point nicely with a slight blunt and works well for aluminum, no spitting like you can run into with Thoriated tungstens. Good luck and best regards, Allan
Parent - - By swsweld (****) Date 03-26-2015 19:19
Hello Allan,
We  completed the weld last week with some difficulties. The suggested Ceriated tungsten was the better choice especially for the open root pass. It directed the arc better than the balled pure tungsten. Bridging the gap was much easier with the sharper Ceriated tungsten.  RT showed some porosity and some tungsten inclusion. The Hi-Freq arc start wasn't working henceforth the tungsten inclusion. At least that's my story and I'm sticking to it haha. And AL is very susceptible to porosity on RT's.

Fortunately, the 2" root ID was accessible from the inside of the vessel for visual inspection and minor grinding so that was a big plus.

At the end of the day, it passed RT and can be placed back in service.
One note, there was a third of the pipe that just did not weld like the rest of the pipe. That is the unknown variable when welding on materials that have been in service for decades. You just don't know until you fire up on it...

Thank you for all of your help. It was greatly appreciated.

Tim
Parent - By aevald (*****) Date 03-27-2015 04:21
Hi Tim, thank you for the update on this project. As has been the case in many repair related issues, there can easily be lost information that relates to the original fabrication, there might also be differences in how the initial welding was qualified(as in different code versions and material availabilities or suggested materials), I believe that there are always some extreme challenges when this sort of thing could be at issue.

I noticed that Al(in a following reply)asked about the particular code and a few other questions with regard to WPS's and likely WPQR's, those questions and their answers may or may not readily exist. For you, I hope that all of the "T's" have been crossed and the "I's" dotted. Glad to hear that you folks made your way through this job.

I did have one more additional comment, I believe that Lawrence would definitely reply in this same manner: Lose the pure tungsten for welding on aluminum, there are just a whole lot of other choices that are just so much better. Best regards, Allan
- - By 803056 (*****) Date 03-27-2015 02:49
Quick question; since this appears to be welded and tested in accordance with ASME (what section?), is the WPS used qualified by testing per ASME? 

If so, how was the WPS qualified if there is a question as to the alloy being welded?

Just asking to see if the mud starts to churn.

Best regards - Al
Parent - By FinishLine (*) Date 03-30-2015 12:53
I worked at a plant that had vessels built to ASME Section VIII, but because the state wasn't a "Code" state, aka national board rules were not the law, repair of these vessels was like the wild wild west. Sometimes they would use repair criteria from NBIC, sometimes they wouldn't, sometimes they would perform NDE IAW Section V, sometimes they wouldn't....really hard to figure out what to expect....I could see this being a similar scenario.
Up Topic Welding Industry / General Welding Discussion / Aluminum Pipe Groove Welds

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