Tungsten Discoloration

I am puzzled by something. I was practicing some TIG welding today, and the tungsten was becoming discolored. The strange thing is that it
was only discoloring INSIDE the gas cup. That is: the portion extending outside the cup is fine, and the discoloration starts flush with the cup, or slightly inside it and extends inward about 3/8" to 1/2".
I am using a 3/8" I.D. gas cup. The tungsten is 3/32", 1.5% Lanthanated The argon is set to 20 C.F.H. The postflow is set to about 10 seconds The tungsten is extending about 1/4" from the cup.
I was practicing on 16-18 gauge stainless steel, using about 50 amps. It seems to me that 20 C.F.H. should be plently of gas, but the welds were showing some signs of inadequate shielding. (Not badly though. Some of the welds looked fairly decent.)
Does anyone know why the tungsten would discolor only INSIDE the cup like this? Thanks much!
Matthew c.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Could it possibly be a tiny, otherwise unnoticeable water leak in the torch head? I have heard that tiny water leaks can cause the tungsten to look funny.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In article

That would be a #6

Good choice.

That is bare minimum for a standard collet body. I would up it to 25 cfh. Or switch to a gas lens collet body and go down to 12 cfh.

A bit low. Postflow is there to protect the tungsten as it cools. The time is set according to tungsten diameter. For a 3/32" tungsten I would go for 15 - 20 seconds.

That is about right. For a standard collet body 3 X tungsten diameter is standard, so 9/32" would be the limit.

Make sure there are no drafts in your shop, and up your flow to 25 cfh.

That is usually caused by contaminating the tungsten by touching it to the base metal or filler rod. The contaminants will tend to wick up the tungsten inside the cup.
Here are some quotes from my past answers to question about TIG:

A basic selection of TIG Rod should include Steel, Stainless steel, aluminum, and bronze.
Steel ER70S-2 The basic TIG filler for steel. It comes copper plated to prevent rust, but keep it in a tube or bag anyway. Sizes: 0.045", 1/16", 3/32", 1/8"
Stainless steel 308L is the standard filler for 304 SS which is the most common type. 309L is a better filler for joining any kind of stainless to steel. 316L is the best for marine work. Sizes: 0.045", 1/16", 3/32"
Aluminum 4043 is the most common aluminum filler rod. It works well for most situations, but... 5356 is stronger, better corrosion resistance and better color match for polishing or anodizing. 4047 is my favorite for welding castings, but it is kind of hard to find. Sizes: 1/16", 3/32", 1/8"
Bronze Silicon Bronze is excellent for joining other copper alloys such as copper, brass and most bronzes. It can also be used to TIG Braze Weld steel and stainless steel. TIG Braze Welding is very useful for stainless steel since it doesn't actually melt the base metal so there is no chromium oxides formed on the back face of the metal. Sizes Sizes: 0.045", 1/16", 3/32"
An advanced selection would include: Some aerospace alloys like Inconel, Hastelloy, or Haynes alloys. They are my favorite alloys for joining odd things and are extremely strong. Pure Nickel is excellent for joining cast iron.. Pure Copper is good for TIG welding copper where it will be seen. ER80S-B2 is the current top choice for TIG welding Chrome-Moly tube for planes, cars, motorcycles and bikes.
As to a vendor. The only guys I know that even list TIG rod on the Web are:
http://www.tigdepot.com
Great outfit, they carry all things TIG.
You can also mail order from Central Welding at :
http://www.centralwelding.com
Just call them and they will ship it to you.
Here is an exercise to practice when not welding.
Level 1
Take a 3/8" steel washer. Place it on a piece of white paper. Take a nice sharp pencil. Place the tip of the pencil against the paper inside the washer. Now start swirling the pencil tip around the inside of the washer to draw a circle on the paper. Keep circling the inside of the washer, while nudging the washer across the paper. Try to end up with the washer traveling in a straight line across the paper. You should end up with a long swirl pattern across the page. Keep practicing until the swirl pattern is even and in a straight line.
Level 2
Same setup, with one change. Once again slide the washer across the page while swirling the pencil tip around the inside of the washer, but now DON"T touch the paper with the pencil tip. This means being able to hold the tip of the pencil within a 1/16" of the paper without touching it and without lifting out of the washer.
Level 3
Do Level 2 while standing next to the table without any part of your arm resting on the table.
Level 4
Move to a 1/4" washer.
This exercise comes from a welding textbook from 1929, and it still works quite nicely to train your muscles for floating the torch.
Normally I do not swirl the torch while TIG welding, but this still works as an exercise to build up muscle control.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Excellent post. Thanks, Ernie!
Ernie Leimkuhler wrote:

--
John L. Weatherly
Nashville, Tennessee
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks for the excellent reply! I will try the changes you suggest.
Matthew C.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.