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Porosity in dissimilar metals

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Porosity in dissimilar metals

Postby bkm659 » Tue Oct 03, 2017 4:02 pm

Unfortunately I just failed a UA41 test ( schedule 80 2"carbon steel pipe with 309ss filler, 6g). They said that I had porosity. I have a tendency to overheat because I am not as proficient at walking the cup as I would like to be. It feels like too much going on at once but I am getting better. My initial reaction was of disbelief. Porosity in a tig weld? I asked the instructor and he couldn't give me a good answer. My inclination is that I am just overheating and need more practice with my hand movements. My root is shiny, but hot pass and cap always seem to coat with oxides and are dull. Any thoughts?
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bkm659
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Re: Porosity in dissimilar metals

Postby Coldman » Tue Oct 03, 2017 4:41 pm

What are your settings?


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Re: Porosity in dissimilar metals

Postby Poland308 » Tue Oct 03, 2017 6:44 pm

Let it cool enough to touch it with a gloved hand between every pass after the hot pass.

Edit: are you wire wheeling between passes? And are you clipping the oxidized end off your filler when you start back up?
I have more questions than answers

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Re: Porosity in dissimilar metals

Postby bkm659 » Tue Oct 03, 2017 9:57 pm

I am set at 95 amps for my root. I feel like I should turn it up a little more on the hot pass and cap but I never do. I set a 3/32 gap with 1/8" filler using lay wire. Usually I will quench between passes because we are only X-ray. I definitely clip my filler every time. I may not wore wheel as much as I could.
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Re: Porosity in dissimilar metals

Postby Coldman » Tue Oct 03, 2017 10:45 pm

2" is easy to overheat. For sched 80 I would increase fill/cap passes by 10 amps and travel faster. Do you have to walk the cup for the test? If not use the method that you can travel fastest with comfort. Get motoring. For 2" I would use 3/32" wire.
You don't mention gas flow rate, make sure you have enough cover to avoid contamination. For your test crank it up if you can.
I would definitely wire wheel each pass for the test.
Quenching a test coupon is not a good idea especially if x-rayed. You will have undesirable grain growth that will show up and there is the chance you will suck in crap and water from the bucket into pores that can cause contamination on the next pass.
Quenching is only used on practice pieces to save time.
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Re: Porosity in dissimilar metals

Postby bkm659 » Wed Oct 04, 2017 7:08 am

More heat and move faster... that was the next step I think. I do not HAVE to walk the cup, it is recommended because the instructors want us to learn to weld that way because of the speed and control but they wont smack the torch out of your hand or anything lol. I use #4 for root, #6 for filler, and #8 for my weaved cap. No gas lens, just straight cups on a 17 torch set at 15-17 cfh with about 10 cfh purge. I am purging from the top though. My instructor had me set up that way to make inspection inside of the pipe easier. That may be a non issue because my root is good and shiny inside and out. I do continue the purge for the entire process also. Tonight I was planning on trying two stringers for the cap. I think that I will do one coupon freehand tonight also to see if I can control my heat input better. It was funny, the test proctor inspected my coupon and asked why it was so lumpy. I assured him that it was probably skill level! I'm not 100% comfortable walking the cup yet. I set to perfecting walking the cup a couple of months ago and I just stuck with it for the test. BTW, I usually use 3/32 309 filler for the hot pass and cap. The other thought that I had had was pulling in too much base metal to the puddle. I may be digging in a little too much on my hot pass into the carbon steel bevel. Just a thought. Thank you guys very much for your input. It really pissed me off when my instructor didn't have an answer to why I failed for porosity. I knew that I would get some help here and I appreciate it!
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