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Up Topic Welding Industry / Technical Discussions / Porosity GMAW Troubshooting
- - By Lawrence (*****) Date 04-22-2015 12:35
Plain Carbon steel
.052  L56
88/12  Ar/Co2
280 Amps  27 volts  (spray transfer)
Regular old Hypertherm PAC in good condition.

Joining Flanges  CJP V groove 55 degree included angle (hand cut PAC) with CAAC backgouge and fill.
Plate thickness from 3/8-1inch.    Typical 99+ Percent first pass UT yield on a daily random regimen.

Observing porosity on root pass of V groove.

Plates hand beveled (expert worker)  Clean cuts, brushed and clean of hard slag  (no grinding).  Typically a good fat 1/4" root face (land) left on the pieces to avoid burn-thru on root passes. (Yes we have a PQR for this operation)

Plates butted together with zero root opening and the V-groove is filled (side 1), the assembly is then turned over and backgouged to sound metal.  (Note there is zero visible porosity on the root and fill passes of the V-groove (side 1)

At this point is when we observe the porosity.. (internally)  Full length of joint, from small to 3/32 pore size...  If we gouge further it is removed completely, but not much of the backing weld left.

When we grind the reinforcement off of the Root passes (side 1) there is no porosity all the way to flush with the base metal.

Control assembly of 3/8 plates butted square groove style with no bevel were welded... Side one single pass, flip assembly, gouge and backweld...  Zero defects.

Only the plasma beveled parts are showing this internal porosity.  I would say the porosity is at the fusion line of the first pass.

Grinding or Flapper wheel applied to root faces will fix the problem..... But...But...But,,,  They have been doing it with perfect success for quite some time with the root faces simply chipped and brushed...

Solving the defect is one thing... Discovering the root cause for the porosity is something altogether different...   No plant manager wants an extra step, tool, consumable added to a process that has been working with a 99+ % UT first pass yield.

GMAW equipment good
Gas supply tight

Something changed!

The compressed air is always wet,,, It would evaporate on the hot base metal after the PAC anyhow.

Could oil from the compressed air leave a residual even through a plasma column?   Nothing visible, but I'm grasping at straws.

Going to swap plasma cutting units today to see if that makes a difference.

Any thoughts, suggestions, similar war stories>???

Need some Sherlocking here friends.
Parent - By Blaster (***) Date 04-22-2015 14:19
Have you changed the gas cylinder?  Once in a great while I get a bad bottle.
Parent - - By Blaster (***) Date 04-22-2015 14:22
Also, any chance the gas solenoid in the machine is failing or partially / intermittently sticking?
Parent - By Lawrence (*****) Date 04-22-2015 14:59
Tried several power supplies, no change.

Gas is bulk mixed with brand new mixer... The other 75 or so units working fine.

Also, if it was a mix or solenoid issue, I would expect to see the porosity on the weld face at least from time to time.

Leak check of shield gas from the flow meter show good.
Parent - - By aevald (*****) Date 04-22-2015 14:47
Hello Lawrence that sounds like a frustrating one alright. Okay, so you mentioned "chipping" is this by way of a needle scaler or similar pneumatic tool? If so and if it is a front exhaust tool, there is the possibility of an introduction of oils through this process.

As to the oils from the compressor making their way through the plasma column: I would say possible, but I believe that you would see some indications of that by way of the quality of the cutting arc and also consumables deterioration.

You also mentioned brushing: would this be hand or power brushing and of course the age old question as to whether there is any possibility of contamination from the brushes? Even if these are dedicated tools is there any way that they could have been laid in or on something that could have contaminated them, or maybe not be so dedicated and have cross-contamination present?

On the ones that were butted and welded and then back-gouged and showed no indications. Were these welded with the same machines as the ones that had the indications after the plasma prepping/chipping/brushing?

This might sound a bit strange, but were any of these machines equipped with the wire-wipers? If so, has anyone used anything on these wipers to renew/treat them recently? Are the welders using nozzle dip?

I know, questions, questions, but you definitely have one here that doesn't jump out and say anything to you specifically. Be looking forward to updates and also others comments on this. Good luck and best regards, Allan
Parent - - By Lawrence (*****) Date 04-22-2015 15:48
Typically chipped with needle scaler if there is hard slag or just a hand slag hammer most of the time.  No power brush.  

Some of the cuts are so clean the scaler is not used, so I'm checking that one off.

There is stupid mig dip on the cart, but I haven't seen it used.   In our shops that have GMAWP I have banned mig dip.  "Just make a spatter free weld Johnny"  I don't think this is a factor because the square grooves are fine.  Also Mig dip porosity is usually open to the surface  :)

Yes the square grooves with no porosity are made with the same power supply and sometimes the same base metal... Thin to thick on one end and thin to thin on the other.

No on the cross-contamination.  They are moved directly from the stack to the line, literally a few steps.  (good flow layout for once)

The Bar line (shear tool) does leave a drop of oil from time to time on the stock, but that is easy to see.  The drops are not getting on the cut areas.   The blade has some oil/grease on it, but I'm not seeing residue on the cut surfaces.   This does raise the question; should shear blades be oil free?   I don't know.   I was hesitant to ask them to degrease it.

There is enough thickness to the backing welds to gouge the porosity out and not burn through.

The thing that gets me is that the day before yesterday the welds were perfect.
Parent - - By aevald (*****) Date 04-22-2015 16:06
I can see where that would be really frustrating. I guess all I can say at this point is that either it will "mysteriously" disappear as quickly as it showed up or you will determine the cause. Good luck and best regards, Allan
Parent - - By Lawrence (*****) Date 04-22-2015 16:08
It's all I can think about  ....some.........simple.........thing
Parent - By CLH1978 (**) Date 04-22-2015 16:57
Hi Lawrence. Just going to throw some thoughts at you.
          Travel speed change.
          Electrode stickout.
          Correct CFH
          Try another supply of filler material
Parent - - By kcd616 (***) Date 04-22-2015 17:11 Edited 04-22-2015 17:14
Lawrence,
I am going to do a Kent thing and post a simple stupid thing
how old is the compressor?
might be  leaking oil, into the tools and plasma
I will be wrong:red: but start at the first point
and try electric grinders and chippers to finish
sincerely,
Kent
Parent - By Lawrence (*****) Date 04-22-2015 18:41
This was a thought for me as well... I'm not sure how to test it though??????

Maybe just hold the plasma torch about 6 inches above a dry piece of steel and pull the trigger and let the compressed air flow and the pilot arc fire off... just do it a few times and see if the compressed air stains the base metal below.

Gonna go put on my hardhat and try that right now.
Parent - - By jarsanb (***) Date 04-22-2015 18:27 Edited 04-22-2015 18:41
If YOU are asking for help with GMAW then it must be something extra out of the ordinary. If it was shielding gas, cfh, electrode, solinoid or any of the constants then the porosity would be random and not isolated to this one pass or layer. So if the porosity is only in this one pass/layer then what is different for this pass? I would have to verify electrode extension and work/travle angles. Also, if your using a slip on nozzle and the welder is resting the nozzle on the bevel edge, it could be closing the space around one side of the contact tip for that pass disrupting gas coverage. Your positive it's not intermitten Inadequate Fusion along the root face, cause it sure sounds like it from what I'm reading.
Attachment: Doc1.docx (60k)
Attachment: Doc1.pdf (87k)
Parent - - By Lawrence (*****) Date 04-22-2015 18:38
My thoughts exactly!  

"So if the porosity is only in this one pass/layer then what is different for this pass? "


I keep coming back to the PAC beveling...  The process is perfect with no bevels.   

But no porosity on the top edges of the bevels... Only at the root of the first pass.

Porosity is always about contamination.... Always... 100% of the time.....   So, 

What is the contaminant?

How is it getting there?

It's just that simple...  and just that difficult.
Parent - - By pipewelder_1999 (****) Date 04-22-2015 20:34
Air from the root side may be causing the issue.

A quick "Test" may be to purge or shield the backside. The gap may be tight enough that the heated air is trying to escape from all directions.

Within the past few months I have been assisting a company with porosity on a .059" thick weld on a D17.1 item. Every quadrant exhibited porosity. The area coincided with an area where the faying surfaces were slightly separated. 

Have you tried removing the scale from or cleaning the root face and not just the bevel face ?
Parent - - By Lawrence (*****) Date 04-22-2015 21:12 Edited 04-22-2015 21:16
Root faces freshly sheared, they are on a conveyor literally 20' from the workstation  :(

Zero root opening, they are tight.   No change in processing as far as fit-up.   (that I can discover)

Bar ends are "nipped" so that no corrosion or paint get into the joint.

The faying surfaces (root faces) are often 1/4" thick.  The shallow bevel lowers distortion potential... Backweld pulls it straight.

I really appreciate the ideas all of you are bringing forward.   Thank you.

Probably the issue will disappear tomorrow and we will never know!
Parent - - By Blaster (***) Date 04-22-2015 22:16
Well, dilution with the base metal would be different.
Parent - - By Lawrence (*****) Date 04-23-2015 12:28
Ok Blaster,  dilution is something I haven't considered :)

But I still keep circling back to the square grooves that get a backing weld, flip, gouge and fill weld with no problems... The only time the welders see the porosity is with the plasma cut bevels.  

Can you say a little more about your thoughts on dilution?  

Base metal is ASTM A529 or 572 Gr 55.... Nothing special  filler is L56 so premium stuff for filler.
Parent - By aevald (*****) Date 04-23-2015 14:38
Hello again Lawrence, another shot in the dark here. I take it that you are using compressed air for the plasma gas? Are you seeing excessive deterioration of the electrode/tips in your plasmas as of late? I am asking this due to the slim possibility that the alloys associated with the plasma electrode and tip might be passing through the arc and contaminating the surface of the cut face as erosion of these components is taking place. Then as the welding is taking place these deposits may be volatizing in the arc and creating gas bubbles that won't escape while the puddle is fluid. This could be amplified by the push angle as the arc could be pushing this ahead of the puddle and possibly over-running the volatilized gases and trapping them at the root. As I said, a shot in the dark. Best regards, Allan
Parent - - By TimGary (****) Date 04-22-2015 22:31
I've found sub-suface porosity can often attributed to excess travel angle of the GMAW nozzle.
When the travel angle is 45 degrees or more, the shielding gas flow creates a venturi suction that pulls in outside air to mix in the plasma.
If all other likely suspects have been ruled out, this is often all that's left.
Try making the root pass with a 10 to 15 degree max travel angle.

On a side note, I had lunch today with Gene Crook. Great Guy. Thanks for the recommendation.

Tim
Parent - By ssbn727 (*****) Date 04-22-2015 22:59
Good point Tim... However, Larry already mentioned that nothing regarding technique or any thing else has changed prior to yesterday, and the results were no previous amount of substantial porosity compared to the current results... Which begs to question any change in welding parameters, or technique unless Larry didn't notice this which I highly doubt that he would from what he's already posted.

Respectfully,
Henry
Parent - By Lawrence (*****) Date 04-23-2015 12:34 Edited 04-23-2015 12:52
Tim,

Gun angles are really good...  About 3 months ago I got this line 90 degree goosenecks just exactly so they would have a bit more easy time keeping that 10-15 degree push... They also don't whip the gun anymore...  

We really increased random UT in this area about 4 months ago and even do some Mag particle spot checks on the gouging to make sure they hit sound metal every time.   They thought I was being a Nazi at first, then they saw there UT yield jump to 99%.  Now I'm their friend :)

I'm glad you met up with Gene,  I hold him in high regard, I'll say more in a PM.   If you haven't already, you will probably meet Heidi Brey,  She is also sharp as a tack. Please give her my best regards as well.
Parent - - By ssbn727 (*****) Date 04-22-2015 22:46 Edited 04-22-2015 23:05
Lawrence,

I think from what you have described so far leads me to be looking at 2 locations where the contamination of the metal is originating from possibly either 2 sources or just one... Process of elimination will determine if both locations or only originating from one source of the contamination - yad-yad-yada!:roll::wink::grin: The two I'm guessing are #1.) the air from the compressor tank especially if the air is as you previously mentioned  being "Wet" due to a variety of possibilities which I will come back to later with detailed questions pertaining to the compressor tank...

#2.) The other possible source may be the residual oil from the shear especially if the faces of each cut member make up both members of the root face, but at this point I would like to come back to source possibility #1. and ask the questions pertaining to the compressor,,,

First off, are you using air as part of either a mixed gas used for PAC? Because if so, there is a possibility that even if there is only a slight, or small amount of water in the tank, and the tank isn't drained daily from wherever the drain valve or plug is located which is usually the bottom of the tank... I have also seen the drain valve, or plug located to the side of the tank and above the tank bottom sometimes when I would go service a truckload of Linde, and Thermal Arc, or Hypertherm and the early Miller models of air supplied plasma cutters at the many customers back in the day when I used to service them many moons ago... Good call Kent.:grin:

Those drain valve or plug locations gave me a quick reason to doubt whoever was maintaining these systems if they were doing so properly... Duhhh??? And needless to say, a quick change of the location for the drain valve or plug to it's proper location in order to perform an also proper draining of the compressor, resulted in solving the problem of contamination along with having an in line air and oil filter located close to where the output line connected to the PAC... In other words don't just look at the obvious when diagnosing these sort of problems even though most of the time they may just be staring you in the face...:eek::grin::smile::wink::cool:  Okay, let's focus on the other possible source which is residual oil from the shear.

You wrote this: "Root faces freshly sheared, they are on a conveyor literally 20' from the workstation  :( " And then Gerald posted this: "Have you tried removing the scale from or cleaning the root face and not just the bevel face ?" Here is where I think that Gerald is on to something because if the root faces aren't at least checked for any residual contamination like the oil you mentioned previously that you discovered in an earlier post by posting this:

"The Bar line (shear tool) does leave a drop of oil from time to time on the stock, but that is easy to see.  The drops are not getting on the cut areas.   The blade has some oil/grease on it, but I'm not seeing residue on the cut surfaces.   This does raise the question; should shear blades be oil free?   I don't know.   I was hesitant to ask them to degrease it." they do usually have a little but not so much that would lead to possible contamination if the sheared faces are cleaned afterwards with a quick wipe or degreasing of some sort to make sure...

Well I looked at the 2 posts where you mention the shear blades some oil/grease on it, and then in another post before that one regarding the root faces being freshly sheared... It kinda makes me wonder about what you're describing so if you can clarify this in order to avoid any possible confusion it would be most appreciated... Now this nothing more than conjecture at the present so one needs to eliminate any and all of the possibilities as the source of contamination and these 2 locations are good place IMHO to start.:grin::smile::wink::wink::cool:

P.S. So at this point, are they grinding the faces clean or are they backgouging instead until you solve the problem?

Respectfully,
Henry
Parent - - By Lawrence (*****) Date 04-23-2015 12:49
Ok Henry,   And thanks for the thoughtful reply :)

I think you may know more about this one than I do, so please allow me to put you into my head for a minute and you can tell me if I'm all wet.... Heh.. get it .. Wet?   ...  Let's say there is wet air... Lots of wet air in the compressed line to the plasma cutter..  My thought was that even if the air were wet, that the resulting heat from the plasma column and the heating of the base metal during the cut would evaporate any moisture...   

My reasoning for the above is similar to an Oxy-fuel rig...  H20 is a byproduct of Oxy-fuel combustion right?   We see the moisture deposited on cut steel when the dew point allows it, and then the heat from the cut causes it to evaporate.  But the H20 is ALWAYS there when the torch is lit...     So I've given this idea of your some thought as well...  Do you see any holes in my reasoning? 

Now to the shear,  I would think if the shear were leaving gunk from the blade on the faying surfaces that it would show up on square groove welds and beveled joints as well, but this is not the case...  The only problems come with the plasma cut bevels.

Yes,   we are grinding the faces... But it would be preferable that grinding be a "countermeasure"   I don't want to add a process step of grinding when 3 days ago they were doing it without grinding and getting excellent results.
Parent - By welderbrent (*****) Date 04-23-2015 14:49
Because moisture will often form from the volume and temp changes in the lines regardless of the material used for compressed air lines, I used a special filter AT the plasma so I only had the short run to the gun from the machine and seldom had any issues there.  My Lincoln plasma had a factory filter that I did away with and just used the after market.  Kept enough oils and moisture away to increase consumables life and keep the cut materials cleaner. 

Consider, I live in the high country of AZ.  Our humidity is often LOW, as in teens or even single digits.  We still get moisture in lines. 

He Is In Control, Have a Great Day,  Brent
Parent - - By Blaster (***) Date 04-22-2015 23:05
Laminations can give some horrendous porosity.
Parent - By Lawrence (*****) Date 04-23-2015 12:49
No laminations, but you just gave me an idea..

More soon

Thank you sir.
Parent - - By Lawrence (*****) Date 04-23-2015 18:19 Edited 04-23-2015 18:26
Fins !

Thank you Blaster !

The first drawing I posted was slightly errant... The backweld was a single bevel and that is the key!
Parent - By Blaster (***) Date 04-23-2015 19:19
You are welcome!  Thank you for the nice explanation of what it was.
Parent - - By aevald (*****) Date 04-23-2015 21:46
I'm with Blaster, nice explanation and as I believe that you inferred: something simple once you figured it out. Best regards, Allan
Parent - By ssbn727 (*****) Date 04-23-2015 22:43
Good one Larry!:grin::twisted::lol::smile::wink::cool:

Well now this a is quite a bit different than what was originally described and posted but, now that image is available to us the reason makes perfect sense now... See what happens when this little extra bit of information that is critical in seeking the root cause to a problem is left out? yet it is unavoidable because of the rush to solve the problem at times which does at times cause temporary blindness.:eek::roll::grin::lol::smile::wink::cool:

Getting back to the shear for a moment... my guess is the space between or lack of needs to be adjusted in order to eliminate those fins... I would also double check to make sure that the capacity of the shear isn't close to it's limit and if so, then a stronger shear is needed...

With respect to the gap between the faces and any "fins" that were left on the sheared faces... If lubricant or even moisture was getting trapped previously then either would be the reason for contamination... If none were present then it would be the venturi effect as Tim and others described in previous posts... In any event, you need to find the source & type of the contamination in order to properly correct the problem, and then add a schedule of preventive maintenance and QC so that whatever you end with as the source of contamination can be consistently prevented from occurring again during production therefore ensuring QC.

Finally, like I said in my previous post, "don't just look at the obvious when diagnosing these sort of problems even though most of the time they may just be staring you in the face." this saying is definitely applicable in this situation...:grin::cool: I'm glad that you found the cause hopefully because of the reason you posted... But, I would make sure that the root cause is just the fins alone, and not the space between the shear faces... And the fins being a possible location where an external source of either moisture, or hydrocarbons or even a mix of the 2 can accumulate.

Respectfully,
Henry
Parent - By aevald (*****) Date 04-24-2015 16:55
Hello Lawrence, I would only throw one more suggestion into the mix here. Have you considered going with metal-core filler wire? My reason for the question has to do with some of the characteristics of this type of filler. I believe that it is known for it's ability to weld through contaminants without some of the issues of the other fillers.

Many moons ago one of the Lincoln reps. showed up for a welding instructors conferences that we had, it was at the time when the metal-core was first coming on the scene. During our conversation with him and his demonstration of the new product, he made mention that one of the incentives for the development of the wire was to deal with pre-cleaning on items manufactured from tube steels. The metal-core was very tolerant of welding on tube steel that had not had pre-cleaning of it's surfaces of the anti-rust inhibitors and metal working fluids that are so often prevalent on the surfaces of these products.

So I guess I am wondering if this might not deal with this sort of challenge in your case. Best regards, Allan
Parent - - By kcd616 (***) Date 04-24-2015 19:33
Lawrence,
another Kent, stupid and will be wrong post
compressor is bad
needs air dryer and filters
try running the plasma with nitrogen
and electric tools for clean up
that will tell you if it is the compressor for sure
lucky I like you
if it was Brent or Scott charge them big $$$$$$$$$$$$$$$ for this info:wink::razz:( love ya Brent and Scott:grin: and not in unmanly way:wink::cool:)
hope this helps
sincerely,
Kent
Parent - - By Lawrence (*****) Date 04-26-2015 05:51
It's fixed Kent.

Didn't cost a nickel :)
Parent - - By kcd616 (***) Date 04-26-2015 17:18
Lar,
I wanted Brent's 2 tin pennies:wink::cool::razz::lol:
sincerely,
Kent
Parent - - By welderbrent (*****) Date 04-27-2015 18:37
:lol: :wink:

Just sitting by and watching the fun.  I could use some BIG Bucks though Kent. 

This has been informative.  Many good suggestions and courses of action to find the problem.  I'm just curious to see if the source was truly discovered of if this comes back around again.  :eek:

Brent
Parent - By kcd616 (***) Date 04-29-2015 17:47
Brent,
to quote you
he is in control:cool:
use what is there
and make all we can of it
sincerely,
Kent
Parent - By bozaktwo1 (***) Date 04-22-2015 16:53
Could the gas flow in the more restricted space of the root pass cause enough turbulence to suck in some air from outside the envelope?  Or could it be sucking air from the backside?  I know this would likely be prevalent on the surface as well, but it's worth a shot looking at it.
Parent - By Jarhead1 (**) Date 04-24-2015 12:53
Lawrence -

We used to grind off all the dross from plasma cutting to bear metal, had a similar issues in the past.

http://www.thefabricator.com/article/plasmacutting/you-can-plasma-cut-it-but-can-you-weld-itr

Thank You -
- - By welderbrent (*****) Date 04-24-2015 16:13
Interesting thread to show a process of troubleshooting. 

Great pics and result.  Hopefully you do find that to be the problem and it will now go away.

Brent
Parent - - By Milton Gravitt (***) Date 04-25-2015 14:42
Lawrence when you find out the cause of the probable please posted. I would like to know what it was.

   M.G,
Parent - - By Lawrence (*****) Date 04-26-2015 05:53
I did,   Two days ago :)
Parent - - By Milton Gravitt (***) Date 04-26-2015 19:53
Thanks Lawrence for reminding me of that because like you said its being two days ago my memory is short now but I went back and read it again maybe I  can remember it when I need to.

      M. G.
Parent - - By Lawrence (*****) Date 04-26-2015 20:37
We are doing increased UT on the line Milton, and for 3 days straight. O defects.  So I'm feeling pretty sure we found the root cause .
Parent - - By ssbn727 (*****) Date 04-27-2015 18:47 Edited 04-27-2015 18:51
So what was the source of those pesky "fins" Larry? And what did you find out that confirmed what the contaminant was?

Did you find out what was the reason those fins were being produced from the shearing operations?

Respectfully,
Henry
Parent - By Lawrence (*****) Date 04-27-2015 20:14
Contamination was just the particles/dross from the plasma cuts being blasted into the fins little gaps.

The bar-line shear must cut flange plate from 10ga to over an inch thick...    The design of the shear is not one that easily accommodates adjustments.

If the shear is set-up to cut 10 gage it leaves awful cut quality on the thick stuff.

If the shear is set-up to cut very thick stuff it leaves a bad distortion on the thin ends.

Soooooooo a happy medium must be "calibrated" into the settings for thickness on the shear blades...  This is what crept off track, as is often the case with equipment that is not brand new, causing fins that were gathering particles.

In-process additional checks are in place, with the welders now understanding that when fins appear that there is a problem with the shear that needs attention... Furthermore that the fins must be ground flush prior to splicing when they are seen.

They will be doing increased UT with daily reporting for at least the next month to make sure things STAY on track.
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