Question about autogenous welding issues in T316L/T304L

[PLCRookie]

I am looking to test some SS tubing to determine the sulfur and other elemental component levels. We are experiencing some issues with consistent penetration in our welds, and it seems to be primarily confined to a certain batch of tubing. Although I have test reports for the material stating that it is within our spec., Im sad to say that I do not trust the reports. What test method can be used on this material to determine the true contents. I would like to do some testing, but I feel like I need more info. first.

Thanks to all

 

[metengr]

Send a piece of the suspect tubing to a local metallurgical services lab for a complete chemical analysis, not a PMI, a complete chemical analysis.

 

[unclesyd]

Could you better describe your welding process and configuration of the weld?

 

[PLCRookie]

The process is Autogenous welding, fusing two sections of tubing or pipe together with no filler rod. The parts are tacked together, then placed into a positioner. Sheilding gas is introduced inside the tube or pipe to purge the backside of the material, and the tube or pipe is TIG welded in one pass, with full penetration. The welds are then polished out ID/OD. We have problems getting full penetration on some batches of material, and we have been able to repeat the problem with this material. I am currently getting a full chemical analysis on two batches, so I hope to learn something there. I am also working to eliminate any process variability such as tip to tube (arc length) variations, as our TIG torches are held manually by the welder. We have an approved WPS that has been used successfully for years, but occaisionally, we still have problems. Our products are usually custom fabricated assemblies, so mistakes are costly.

Thanks for your help.

 

[PLCRookie]

Also, the tube or pipe is in the vertical position with the TIG torch horizontal. We are using Hydrastar (5% hydrogen) sheilding gas on the welding side. The material is .035" to .120" wall thickness.

 

[stanweld]

Have you thought of using fully automatic, programmable GTAW tube welders? Welding parameters can be much more closely controlled with these systems than you described using a manually held torch and manually tack welding.

 

[PLCRookie]

You are talkig about an orbital welder. Yes, we have looked at those, but they have their limitations for our kind of work. Not to mention that they run about 30-40K.

 

[unclesyd]

When doing autogenous welding of thing wall tubes there is one
parameter that isn't to be violated. The tube end have to be
square and flat and, "No Bevel of any sort". you cannot
break the edges of the tube either on the inside or outside. Any
chamfer on either side will result in lack of penetration or incomplete fusion or concave cap. It is best not to tack weld a tube to tube weld.
We used De-Staco clamps to hold the tube while welding with the orbital welding head. We air tested right after welding and later hydrotested 100% of the tubes, even though it wasn't needed
You can beat your quoted price for orbital tube welding head as we have two and I know we didn't pay that much for either one

Also you can rent some brands of machines. The two companies below will rent or lease their equipment

http://www.arcmachines.com/products/fusion-welding

http://www.tritool.com/tube_squaring.asp

 

[EdStainless]

even small variations in S will lead to different degrees of weld fluidity and resulting penetration.
If you set weld parameters to assure full pen in low S then you will have ugly weld shape when you get higher S.

Look at orbital weld heads. The control is much better.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[PLCRookie]

I agree that I could have more control with orbital, and that my current process has limitations. I guess we will continue to observe and refine the current process while we wait for the chemical test results to come back. It may well be that we have to tolerate this issue if we decide to continue welding this way.
Thanks for your replies.

 

[unclesyd]

I don't think S is your problem as we have safe ended a couple thousand tube and I have never seen anything other than operating parameters affect the weld. We have welded self mated tubes, 304L/inconel, 316l/Hastalloy C, 316L/Al6XN. The majority of our tube welding involves 304l/304L.
I would definately try to get an Orbital Welding Head by hook or crook.

 

[PLCRookie]

Anyone out there doing this on a daily basis? If so, could you suggest a IPM for welding T316L tubing? I think that our speed (ipm) is too slow, and (according to the parameters we use) varies depending on the diameter of tube. Im thinking that the ipm should be consistent for all diameters of the same wall thickness. Again, keep in mind that I cannot change the weld current during the weld (as in orbital). I want to start at a defined ipm, and work from that point.

 

[stanweld]

Have you thought of welding in the 1G rotated position? Small postioners are available. The torch can be set for optimum volts/amps without a welder holding it. Travel speed can be set exactly.

 

[PLCRookie]

Stan,

Yes I have. We actually weld in that position (infrequently) for longer parts, so I have a spare positioner I will use for testing these new parameters. I am trying to find a device(torch holder)that has a wheel that rests (or rolls) on the tubing as the part turns,allowing us to set the tungsten distance, and not have to worry about concentricity issues that we have with the chuck and various fixtures that we use to hold different shapes of parts. So far, I have only found one that looks like it will work, but Im having trouble getting info. on it. That device will only work in the vertical orientation, but I think that is the way to go to eliminate the variation of arc length we currently have.

 

[unclesyd]

Go to your favorite welding consumables store and checkout a torch roller guide. There is a nice metal wheel in this set.

Before orbital welding came along we built a welding lathe, actually two 3 jaw chucks with both rotating off a common shaft. The torch was mounted between two parallel bars with a hinge on one end. We had an adjustment screw on the bars to set the standoff distance. We mounted the torch on the side of the tube away from the operator to where he had clear view of the arc.

 

[PLCRookie]

What are the possible issues with quenching the material in water after welding? We typically dip the parts in a bucket of water after welding (yes, still hot). Im told that this is to stop " carbide precipitation", however, I don't really know enough about metallurgy to say any different. I can't help but think this is not a good thing.
Any facts to confirm or deny this?

Thanks again for your help.