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Up Topic Welding Industry / Technical Discussions / Need some Input on these Inconel 600 Orbital welds
- - By Kix (****) Date 07-25-2016 17:43 Edited 07-25-2016 17:46
So here is my issue. Pics below. Notice the difference between the clean no oxidation orbital welds and the welds with oxidation. Processes, procedure and weld program were all identical. Only differences were the time of year welded and the lot number of the material welded. Clean no oxidation welds were welded in march low temps and low humidity. Oxidized welds were welded in July of this year. Very hot and humid 100 deg temps and high humidity with high dew points. Thoughts on the root cause of oxidation. A key note is that this is also happening on the inside of the purged tube.

Some small details of the operation.

.051 wall .500" dia Inconel 600 tube.
GTAW orbital welded using a cobra tig 150.
Heavy wire brush for surface prep inside the tube and out with an acetone wipe down before welding.
Using High purity 100% argon 99.9999 pure for head purge and I.D. tube purge.

No oxidation tie in


No Oxidation weld


Oxidation weld toes and HAZ 1


Oxidation weld toes and HAZ 2


Oxidation weld toes


Oxidation tie in
Parent - - By TimGary (****) Date 07-25-2016 20:42
Had a similar issue on orbital welds for high purity SS a while back.
The root cause wound up being gas contamination.

1. carbon steel screw pipe is bad manifold material for high purity systems as any leak, no matter how small, allows both gas to escape and air to come in.
2. any time the gas pressure is shut off and air/moisture is allowed into the system, oxidation inside the manifold causes issues later on.
3. typical green gas hose is actually permeable and allows contaminating air to get in.

So, your gas is only as pure as the lines that carry it. Any leak along the way adds to problems.

The attached photo shows how to tell how much oxygen is in the shielding gas through reading oxidation color as a gage.

Tim
Parent - - By Kix (****) Date 07-26-2016 11:32
We trouble shot for leaks and didn't find any. We're using those poly plastic looking hoses that cam with the machine to purge and run into the back of the machine. The same bottle of gas was used in March as was in July to run all of the welds you see. We just swapped out tanks on Monday and went to a higher purity and still are getting the same results. I'm baffled..
Parent - - By TimGary (****) Date 07-26-2016 12:25
Ok, so if there is positively no chance of leaks or contamination upstream of the orbital weld head, then the problem has to be in the head.
The discoloration/oxidation is positively a result of oxygen in the shielding, so it has to be getting in from somewhere. You said it's inside as well as outside? Same gas bottle I presume?
I thought that 99.99% pure gas could only come from liquid?
Could the oxy, (somewhere between 70 and 200 ppm as per the picture I posted) be coming from the purge process? Is the discoloration worse on the inside that the outside?
Have you changed anything in the cleaning process?
Is there some type of gap in the orbital head housing?
The point is that outside air humidity can only be a culprit if it is allowed into the weld area.
These are probly all things you've checked already, just spouting off ideas to try and help you figure out what to re check.
When you find the problem source, I bet it will be one of those forehead slapping moments....

Lawrence!!? Are you still here? Or completely fed up with AWS BS...?

Tim
Parent - By Trackergd (**) Date 07-26-2016 14:41
Torn or cut O-ring?  I have run into that before.

Also with the plastic hoses, if they are push to connect fittings rather than compression, I would be testing them.
Parent - - By Kix474 (*) Date 07-27-2016 13:47
Nothing is the cleaning process or anything about the process has changed. With the dewpoint being as high as it is lately and with the acetone wipe before welding, could the tube be chilled with the acetone to dewpoint temp where it starts to form a small skin of moisture on the tube? Thoughts on that? We've checked for leaks everywhere except inside the head also. Yes, same gas bottle and continues to do it with the new gas bottle we just put on.

Does anyone know what the calc is for parts per million when your 02 meter only reads in percentage and down to .1%

Thanks,

Ray C.
Parent - - By electrode (***) Date 07-27-2016 14:00 Edited 08-28-2016 14:44
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Parent - By Trackergd (**) Date 07-27-2016 17:53
Electrode, those are some great points about the hose.   We had an issue a couple of years back with the popular push-to-connect hose fittings, where you force the hose into the fitting and then pull back to lock it.  We had leaks like mad.  Had three issues at once a) contamination in the fitting from the manufacturers machining process b) hose was not seating up against the O-ring inside the fitting and c) hose durometer.   The hose was too hard for the gripping teeth inside the fitting and our folks were not cutting it off square so it was not sitting up against the seal O-ring properly.

Different material hoses have different permeability to gasses and humidity.  The hoses may have been selected based on a weld criteria (gasses etc) other than what they are currently being used for.   Or as the OP noted, the humidity has changed and perhaps is now making it's way into the hoses when the gas pressure is off.

Lastly there is the potential of compatibility of the hose material with the gasses being used and the environment (fumes from welding, heat etc) that is causing degradation of the hose material or the seals contained in the fittings.

I would rule out the hoses and fittings  100% first, then move to the head assembly.
Parent - - By TimGary (****) Date 07-27-2016 17:09
Well, I'm at a loss for any further guidance...
Your moisture theory sounds plausible, testable.
Wish I could be of more help...

Tim
Parent - By Trackergd (**) Date 07-27-2016 17:56
Yes, very testable.

Run the process in an area that has an efficient cooling and less that 50% RH (dehumidifier) and see if the issue goes away.
Parent - By Trackergd (**) Date 07-27-2016 18:00
Can you run an analysis on the tubing when things were OK and the tubing you are using now?  Is it the same batch and/or same supplier?

I know our purchasing department loves to change suppliers and not tell us....usually with less than stellar results.
Parent - - By Lawrence (*****) Date 07-27-2016 16:22
I'm still around... I just must admit that this is over my head.

I would still look at physical things first.

Perhaps the condition of the head, trailing shield, any screens that diffuse the shield/trail gas is different on the later runs vs the early ones.

Different movement in ambient air?   The weld faces all look the same, the color is happening in the HAZ and well beyond...  Maybe even BEYOND any argon coverage at all?

Now if the color is beyond the gas coverage... Purity of gas or leaks or shields mean zero... Then it's the metal itself or something on the surface that is causing those pesky chromium carbides to present them selves and make you feel BLUE :)

Kix is the Man...  I sit at his feet on this stuff anyhow... But I'll spitball a little to keep the conversation going.
Parent - - By Kix474 (*) Date 07-28-2016 11:40
Thanks for the confidence Lawrence! :wink:  So to answer a few more questions that came up above. The only variables that changed between the tubes were the time of year they were welded and the lot number of the material. My next steps are to located some material from the same lot number of the clean welds and analyze the results. I'm also going to check the connections going into the back of the machine again. I really don't like these fittings because they are a push in past a lip and click style connection with a little check valve in them. The further the connection is pushed into the back of the machine, the more gas is allowed to flow through the check valve. Once it clips back on the lip it always ends up depressed the same amount flowing the same amount of gas. This very well could be an inconsistent seat on the inside of the machine. It's MK Products cheapest model. I'll try to take some picks of the connectors and the hose for you all.

Kix
Parent - - By Kix474 (*) Date 07-28-2016 14:42
So I did some more testing this morning. I increased my head pre-purge from 60 seconds to 3+ minutes and was able to reproduce my sweet clean March welds. Problem is, my procedure only allows me to pre-purge the head for 30 to 60 seconds. Changing the procedure would be about a 3 month approval process for the program I'm working on. So now what is the reason why I was able to purge the 02 out of the head in 40 seconds in March and now I had to go to 60 seconds to get the oxidized welds you see in the picture in July. Now to get back to the sweet clean looking welds I had in March I have to pre-purge the head for 3+ minutes. What the hey folks? ha ha Is the gravitational pull of the moon and the temperature of the earth at 800 feet above see level expanding my head parts to the point where they aren't venting 02 as fast as when they were cold and had bigger gaps maybe? I'm pulling at straws here and I'm pulling my hair out. I'm now working on getting our welding distributor to bring out a rental head and run some samples with it to see if I can get back into my 30 to 60 second window. Until then, thoughts on what might be going on?

Kix
Parent - - By TimGary (****) Date 07-28-2016 15:33
Could the problem be with the internal purge, meaning that a longer head purge is needed to help push the oxy out of the internal area?
Leaky purge dam seal causing venturi suction?
Just guessing...

Tim
Parent - - By Kix474 (*) Date 07-28-2016 15:54
The weld joint prep is a square groove with 0 gap. They are butted up tight. The faces of the tubes are machined so there is a perfect fit. Internal purge doe not leak into head purge area and vise versa. Good thought though.

Kix
Parent - - By Trackergd (**) Date 07-29-2016 10:16
What are you sealing the open ends of the tube with?   I dimly remember something back from my Kidde Fire days when we had expanding plugs with o-ring seals.  Not sure what you are using.
Parent - - By Kix (****) Date 08-01-2016 19:26
One end of the tube is threaded so we use a threaded fitting with a purge hose attached to it and the vent end of the tube has a rubber plug in it with a 3/32" hole bored through it.
Parent - - By Trackergd (**) Date 08-02-2016 10:13
I'm probably telling you something you already know, but you might want to take a look at what you are sealing the threads with.  While messy, PFTE paste is way better than the PFTE tape or no sealant at all.  Would also take a look at how good the seal is between the hose and plug as well as the seal between the plug and the tube.

I had to perform hydro-testing of welded components for fire equipment a few years back and ended up using expanding plugs in the ID.  Some are mechanical and some are air pressure operated.  All are available with a pass through fitting for gas or air pressure.  The only thing that can be problematic with this approach is if the tube has an internal longitudinal welded seam.   They are also available that seal on the OD of the tube.  They are designed for production use and have replaceable sealing components.

Careful inspection of rubber seals each use is key as they do wear, tear and cut.

Just so I cover all the bases, I assume by now you have looked at the mill reports on the tubing you are using now and before and found them in spec, so I was wondering if there is a difference in humidity between where the tubing is being stored and where it is being welded.  Thinking about condensation inside the tube, even from something weird like morning dew, overnight to daytime temps, outside storage to inside welding etc...

Hope some of this rambling helps!  :grin:
Parent - - By Kix (****) Date 08-02-2016 14:05
Thanks for the help. I am going to monitor this very closely in the fall when environmental levels drop again. Although, what environmental variables are playing an effect when purging the orbital head out for 2 minutes longer fixes the entire problem?
Parent - By Trackergd (**) Date 08-02-2016 14:31
The two minutes longer is excluding/purging the offending substance.   The question is what is the actual offending substance and why is there less of it in the fall.   My Wild A@@ Guess is humidity.
Parent - By Trackergd (**) Date 08-02-2016 14:40
I had to go dig a bit... 

Argon has approximately the same solubility in water as oxygen, and is 2.5 times more soluble in water than nitrogen

Argon is miscible, so the more water vapor there is, the more it will absorb.
Parent - - By Lawrence (*****) Date 08-02-2016 15:14
It's not a totally unheard of scenario to have moisture migrate up into a GTAW torch.

The titanium tubing shop for Boeing in Everett back in the late 90's used to run a 2 CFH purge in all their manual torches 24/7 as a precautionary process control measure just for that reason.

But I'm still a little skeptical that is your root cause, because it looks to me that some of that coloration may be in a zone that maybe never saw argon coverage.
Parent - - By Trackergd (**) Date 08-03-2016 10:37
I think we probably have hit the two potential major culprits.  Humidity and leakage in the hoses/fittings.   It could be something else.

The only thing I can think of that would be different between winter and summer is humidity.  Of course that may just be coincidence.

I really hope Kix gets it fixed before they lock the door so we have another mystery solved to put in our notebooks for future reference.
Parent - - By Kix (****) Date 08-04-2016 18:12
We just sent the head in today for an overhaul ( new O-rings, solenoid and 2 way valve replacement) Should have the torch head back Monday morning. I like the solubility factor of argon theory. Makes sense that their is much more moisture in the head when the doors are shut that the argon can absorb once it starts flowing into the head, and therefore taking longer for the absorbed moisture to exit before arc initiation. Thanks again fellas for brainstorming this.

Kix
Parent - - By Lawrence (*****) Date 08-04-2016 18:56 Edited 08-04-2016 19:02
Nope, Nope, Nope

Gaskets and O-rings and seals and fittings and gas purifiers will not solve this... I bet.

Lets say moisture did creep up into the head...  Why is the weld face consistent in every image, old or new?   

Wouldn't the weld face itself take on color if "moisture" were the culprit...??

Also,,,  Water does not oxidize a weld or on stainless... Oxygen does...   If this 'mystery moisture' were simply transferring in the shield gas cloud, it would not disassociate and release 02 that would give color...  UNLESS it transferred across the arc, in which case we would see contamination/oxidation on the weld face... But we don't

Only seeing color at the toes and beyond...  The culprit lies there... Something is happening in that zone (maybe gas coverage) but not moisture.

It's something else
Parent - - By Trackergd (**) Date 08-05-2016 11:01
What else would be different between summer and winter?

I am betting that if Kix ran the same process in an air conditioned room with less than 50% humidity, the weld would appear as it did during the cooler weather, but I have lost many a bet before... :wink:

I guess we will see when the head gets back and we get a much anticipated "Kix Update"  :grin:
Parent - - By Kix (****) Date 08-11-2016 19:12
Well, the power source and the orbital head checked out fine. We even bypassed the machine to eliminate connections and solenoids. I still had to go over 3 minutes to get a clean weld. Looks like I'm going to have to wait till the fall or winter to see if I can replicate my March welds and then chalk this whole issue up to environmental conditions.  3 of 48 welds came back with rejectable porosity while in testing we had 100% of 24 welds come back water clear. :-( No bueno..
Parent - By Trackergd (**) Date 08-12-2016 15:03
Is there any possible way to weld a couple of pieces in a temperature and humidity controlled room?  Someones office?  The QC Department Inspection Lab? :twisted:

You would have your answer now, not in the fall.
Up Topic Welding Industry / Technical Discussions / Need some Input on these Inconel 600 Orbital welds

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