Full Pen Butt Welds

[SBK]

I am trying to get full pen butt welds on 50 x 1.5 stainless tube right.
I can get full penetration but am struggling with the colour.
Tube is 304 using 308 1mm rods,arc length is ok and filler kept in gas shield
throughout.
using 37 amps no pulse,1.6 lanth Tungsten,gas lense 7 cup
Have tried with gas from 5lpm upto 10lpm with no real difference.
There seems to be a very fine line between moving quick enough as not to overcook it
and getting the penetration.

Is it necessary or possible to get full pen and keep the colour to gold rather than brown/grey?

 

[Shox Dr]

What is the material and settings

 

[SBK]

soz just edited it

 

[Shox Dr]

You'll struggle without purging, esp if you are new to TIG

 

[SBK]

Yes purging with 4lpm initially then dropping down to 1lpm once tacked up.
will load some pics up probably best

 

[Shox Dr]

pictures speak a thousand words. Until Hotrodder posts a reply, for he is the information god

 

[hotrodder]

thought my ears were burning

There seems to be a very fine line between moving quick enough as not to overcook it
and getting the penetration.

That's basically what it comes down to, just a fine line to walk with regards to heat vs travel speed and (generalising) you're not gonna get the same colours as you would for a fillet without taking extra steps- better shielding (bigger cup, not cranking up the flow rate) or changing the joint set up to lower the heat input needed for full pen with root gaps or bevelling the edges both of which take longer

Heat tint colours go straws/gold, darkening through browns then mottled brown/purple through purples to blues. Then dull grey. The colour changes are due to light refraction as the oxide layer grows thicker
Greys can be avoided without resorting to huge cups/preps etc and are what people usually mean when talking about 'burnt' stainless welds. There's also a lot of utter BS written on the internetz about weld colour. Especially by car guys and expecially on American forums (sorry Americans! )...

If the part in question is gonna see high temps in service then heat tint is gonna happen anyway so weld colour isn't really a big deal unless you're selling exhausts/manifolds to people numpties that judge quality by weld colour alone. If the corrosion resistance is gonna be 'properly' tested then ALL weld colour needs removing anyway hence pickling pastes/electrochemical weld cleaning and the like which restore the chromium rich surface by eating oxides/free iron etc and leaves things as corrosion resistant as they can be. They also make the part look far more finished and professional.
For inbetween cases (not gonna oxidise from heat in use but not be properly tested either) then the weld colour can be easily removed with a stainless brush if you brush it before the weld cools down too much. Doesn't do much for corrosion resistance since you're only removing the light oxide layer but is very quick and easy and looks a lot better than heat tint imo. If the weld's being linished out then it really doesn't matter since you're removing the oxidised surface anyway

 

[SBK]

Aha that answers my question then I should have mentioned it is with regard to getting coded.

 

[SBK]

So I presume then as long as the weld has full pen with no crater defects,no undercut with a slightly raised exterior weld,the finished colour is relatively unimportant ?

 

[biffa]

Just hit it with a wire brush whilst it still hot, those colours only indicate the temperature at which the metal lost shielding, if you doing a coding as well wire brushing the weld will make flaws more visible. Personally I would be purging at a higher flow rate 1pm leaves very little room for error, those colours you've achieved are more than acceptable if you've achieved good penetration. I'm assuming your welding with the touch pointing towards the centre of the tube if you imagine the gas flow will be covering a circular area on the work piece so as your moving along you only have a small distance for the weld to cool before you loose shielding gas coverage, if you tilt the torch back this will create an elliptical area being covered increasing the area being covered and increase the time the weld has to cool before it looses shielding which should improve the colour

 

[SBK]

That sounds logical,so if your welding a 5g position your saying to have the torch inclined away from you ?

 

[doubleboost]

Is that a Boxford lathe in the back ground lol

 

[SBK]

Tis indeed a BUD not a clue how to use it though

 

[doubleboost]

Good machine I have the AUD
Practice makes perfect lol

 

[biffa]

You want it pointing in the direction of travel

 

[SBK]

Got it will give it a go.
Thanks all for the advice,beers on me