Tungsten electrode extension

Date 03-12-2009 13:23

We have a customer that requires us to weld a single bevel,multi-pass GTAW weld in a place that is very difficult to access. Sometimes carbon steel, sometimes stainless. It is on a flange with about a 2 1/2" diameter and a wall thickness from say 1/2" to 3/4". There simply is no way to get a torch into this area at the proper angle and with what I feel is a proper electrode extension of about 5/8" max. You can get it with an extension of about 1 to 1 1/8" extension. We have done cut ups on this joint that have had lack of fusion, crater cracks and some porosity. I feel these problems are stemming from the excessive electrode extension.Trying to get them to let us use another process, like FCAW. What is your opinion on max. electrode extension?

By Kix

Date 03-12-2009 14:14

Depends on if you can get the coverage you need with how far you want to stick it out. I have some cups that I use where I can stick my tungsten out an inch an still get good coverage. Don't know if the cup I use would fit where you need to go though. If you can change the process and have good results, then I'd do that. If you can't get a tig torch in at the prope angle the I'd say you might have a problem with FCAW and getting coverage with that as well unless you plan to use self shielding FCAW. Here's a couple pics of the cups I use.

http://i11.photobucket.com/albums/a189/vdubin474/Gaslenses003.jpg
http://i11.photobucket.com/albums/a189/vdubin474/Gaslenses004.jpg
http://i11.photobucket.com/albums/a189/vdubin474/Gaslenses007.jpg
http://i11.photobucket.com/albums/a189/vdubin474/Gaslenses010.jpg

By jsdwelder (***)

Date 03-12-2009 15:16

Do you think the crater cracks could be caused by the electrode extension or are they usually operator error?

By Kix

Date 03-12-2009 15:35

Are you finding the crater cracks more in the stainless or the carbon steel. You have to really be doing something wrong to be getting crater cracks in carbon. The operator coming out and off of the puddle to quick will usually give you porosity or a butt hole, but not cracks. Are you seeing the cracks coming out of the hole (butt hole) in the crater? If the bead looks good, then I'd say your operator is coming off the crater to fast and tungsten stickout is not your issue. He needs to come off the amps gradually at the end of the bead and let the post flow gas keep the molten puddle covered till it has completely solidified. Issues you will have with to much stickout are, bad gas coverage which will show up in the form of turbulence which will give you porosity in the puddle throughout the bead. Stainless will have a really black nasty color to it when you have improper shielding.

By js55

Date 03-12-2009 16:18 Edited 03-12-2009 16:22

As a specific answer to your question of W extension, no. There is no inherent W extension cause of weld discontinuities, though as Kix relates there are periferal difficulties that must be controlled that can cause discontinuities, like gas coverage.
I used to even bend my W for small SS olets with the cup completely off. The purge made it possible. Removing the cup allowed greater access to the ID and better visibility, bending the W allowed a direct angle on the root of the olet.
Of course the W didn't last very long.