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Up Topic Welding Industry / General Welding Discussion / Sub Arc Porosity Issue
- - By sgtrivas405 Date 08-18-2017 15:33
We've been having porosity issues with our Sub Arc welds for about a month now. we've ground out both web and flanges, changed out flux several times, pre heated metal, changed out wire. Still having porosity issues, any suggestions?
Attachment: WP_20170726_09_54_37_Pro1.jpg (82k)
Parent - - By jwright650 (*****) Date 08-18-2017 15:59
Has the flux been dried? I know you said you changed it, but is it dry. Dry enough not to cause porosity.
Fit up tight, no gaps for air to be introduced in from the other side of the web?
Parent - By sgtrivas405 Date 08-18-2017 16:28 Edited 08-18-2017 16:38
we keep the flux in oven at 300°, bumped it up to 350°. fit up is as tight as can be as well.
Parent - - By Lawrence (*****) Date 08-18-2017 17:35 Edited 08-18-2017 17:43
Edgar,

Are you cutting your webs with a water table plasma?

Those large examples of piping porosity on a Pull-thru (Conrac) weld most often come from an actual wet edge.  Cutting table fluid will make indications like the ones in your pic.

When the flux is over used (cycled so many times the flux is like powder instead of sand) the indications are usually very fine and centerline.

Summertime, sometimes the pace is increased eh?   Maybe the beams are getting to the pull-thru a little quicker than usual?   Maybe it's more humid so things are not drying as quickly?
Parent - - By jwright650 (*****) Date 08-18-2017 18:13
L,
He mentions heating the steel....so, I'm thinking the steel is dry.
Plasma cut edges (any dross that is left) are porosity makers too, but he says they have ground the web and flanges.
Parent - - By sgtrivas405 Date 08-18-2017 18:30
That is correct John, temp sticks and torches. Ground out nice and clean.
Parent - - By Lawrence (*****) Date 08-18-2017 19:18 Edited 08-18-2017 19:21
Ok,,

'
Preheat...  I know there is no perspective, but the pic looks like a 3/16" or 1/4" fillet...  Why are you preheating?

Is the porosity on one head or both?

What is your weld size call out?

What is the travel speed of the welds in question?   They look convex, which is a little unusual for that operation.
Parent - By jwright650 (*****) Date 08-18-2017 20:11
If I were to guess, I think the preheat was to ward off moisture due to the porosity problems...kind of a last ditch effort to find the issue.
Parent - - By jwright650 (*****) Date 08-18-2017 20:17
Did this issue just start happening or has the SAW track setup changed somehow? Voltage higher? so that the travel speed is faster?

Sometimes with FCAW excessive voltage to increase travel speeds have caused issues like this to suddenly arise. I had guys talking too much during the day and then try to catch up near quitting time. They left one of the FCAW machines setup when they left for the day and I found the voltage way out of the procedure. It just so happens that was the machine that I had been fighting porosity and also worm tracks on.
Parent - By sgtrivas405 Date 08-18-2017 20:34
reviewed WPS and played with the ±% on amps, volts, and travel speed. Almost quitting time. When we figure out a solution I will post on here, thanks for your support.
- - By 803056 (*****) Date 08-19-2017 14:03
They probably didn't use enough preheat to drive the moisture out of the steel! Just kidding. but if they are preheating the steel, there may be condensation wicking up in to the joint and not evaporating before the welding head reaches that location.

I've seen this before where the contractor attached the preheating torch to the welding tractor just ahead of the welding head. The correction was to use two torches separated by about three feet. The first torch (about five feet in front of the welding head) bought up the temperature, but it was insufficient to evaporate the condensation that collected on the "cold" plate. The second torch placed about 3 feet in front of the welding head bought the temperature up to the final preheat temperature and allowed that extra few seconds to evaporate the condensate. "Poof" no more porosity.

If no preheat is involved, i would consider the amount of fines in the flux, especially if the unfused flux is recycled. This is a problem with bonded fluxes more so than with fused fluxes. From the photograph, I suspect you are using bonded (active) flux for the single pass welds over mill scale.

Al
Parent - - By Lawrence (*****) Date 08-19-2017 18:22
I'm trying to get my brain around a preheat setup on not one but two web/flange joints, running SAW simultaneously @ 70+ inches per minute.
Parent - - By 803056 (*****) Date 08-19-2017 18:42
Piece of cake.

Al
Parent - - By Lawrence (*****) Date 08-21-2017 01:02 Edited 08-21-2017 01:10
Your kidding right ?

Where ya gonna put those torches?
Parent - By 803056 (*****) Date 08-21-2017 03:28
Don't need no stinking preheat in Texas!

Al
Parent - - By sgtrivas405 Date 08-21-2017 15:02
We posted a guy with a torch on the back side to preheat a 10 ft section on 25 ft piece. we don't heat every single piece going through our PTW Lawrence. It was just to see if maybe it was the moisture in the material. We've been having this issue for about a month now and so has another steel company down the road from our location.
Parent - By Lawrence (*****) Date 08-22-2017 02:43
It's a super interesting problem!

Especially from hundreds of miles away :)

Is the porosity on both sides?   Just the datum side?   Just the transition side?

I feel your pain.... or at least have literally felt it!

That process is more like a TARDIS than a welding machine eh?
Parent - By Tyrone (***) Date 08-23-2017 11:11
Hey Edgar,
What is the steel type and country of origin?
Up Topic Welding Industry / General Welding Discussion / Sub Arc Porosity Issue

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