stainless steel tig ????

[weldingboy]

ok guys im going to tulsa welding school and im in phas 8 now and we are doing stainless steel tig on a 2'' schedele 40 pipe and im having some issues with instructors i just cant get the same anwser from them i run my root at about 110 and hot pass and fill at 125 and the cap at 140 it always turs out silver and blue and not gold so the instructor i have now is giving me lower grades than everybody else because its not gold but other instructors says silver is better than gold i need some help does anybody kno the right color thanks

[Rojodiablo]

So long as your backpurge is good, your toe is wetted in properly, and you have good puddle shape and penetration, you should not have any problems. My better welds are usually gold/ silver colored, my bad ones are blue, and my really bad ones are black......with chunks of tungsten melted into them!!!

[WHughes]

What are you planning to do after you are finished with school?

[sn0border88]

Your welds are silver and blue? Thats odd, because those are on the opposite sides of the color spectrum. I would expect to see some inbetween colors as well. Technically silver is ideal, because it means that the weld material was relativley cool when the shield gas was removed. Blue is at the high end, and though it wont be a problem on stainless if you see blue on TI welds, they fail.

However I agree with the above, color really shouldn't matter on stainless as long as the root has a good back purge. Ask them why one is better than the other, im curious to hear their answer.

[snappy101]

i would get both teachers together and get them to sort it out between them

[Drake Aldan]

Ah, for real?

from my experience at the school, the color spectrum for oxidation is silver-blue-gold-purple-grey (purple and grey being bad).

Greg, my instructor for the phase, would usually accept anything from silver to gold with some streaks of purple in it (of course, the closer to cooler the better).

If you are positive that your welds are coming out blue and you want them to turn gold (if you can't convince your instructor that it shouldn't matter), just lower your travel speed/crank amperage up/whatever and let more heat get into the weld. of course, keep in mind all the factors that come with extra heat (larger puddle, undercut, etc.) and compensate for them but if he wants gold more heat'll do it.

[pulser]

The color on and around a stainless steel TIG weld results from the hot metal reacting with the oxygen and nitrogen in the air. If the weld is shielded with inert gas while it is cooled below some threshold it will be perfectly shiny silver with no discoloration, but this is generally only possible in a chamber or automated tube weld head where oxygen is less than 50 parts per million (ppm) or 0.005%.

The amount of oxygen, the temperature of the metal, and the time it is exposed, all affect the degree of discoloration. As condition worsen the color changes from silver (no color) to gold, blue, purple, black, then sugared. Other than providing good shielding with a large nozzle and gas lens, discoloration is function of current, travel speed, and metal thickness, which all affect how fast the weld and base metal cools. A small root pass on thick metal discolors less than it would on thinner metal.

[weldingboy]

Originally Posted by WHughes

What are you planning to do after you are finished with school?

im not sure yet im still looking

[weldingboy]

i got them together and they discused it the instructor i have now hasnt been tiging stainless for long so he really didint kno so joey told him that gold was the proper color but the silver was just a little bit better so they got it worked out

[WHughes]

Thats weak. Are you paying for that kind of instruction?

[Supe]

That's also a lot of heat for 2" sch. 40 stainless...

[i4sillypwr]

Yeah that does seem kind of hot. Do you weld at light speed? Got some pics?

PS. Your instructors sound like they dont know what the hell they are talking about.

[zapster]

Unreal.

...zap!

[sn0border88]

Originally Posted by Drake Aldan

Ah, for real?

from my experience at the school, the color spectrum for oxidation is silver-blue-gold-purple-grey (purple and grey being bad).

If you are positive that your welds are coming out blue and you want them to turn gold (if you can't convince your instructor that it shouldn't matter), just lower your travel speed/crank amperage up/whatever and let more heat get into the weld. of course, keep in mind all the factors that come with extra heat (larger puddle, undercut, etc.) and compensate for them but if he wants gold more heat'll do it.

Sorry, but that's just wrong. Gold is just a shade above silver as far as the color band on stainless goes. If hes getting blue and wants gold he needs to put less heat into the material not more. Travel speed might not be the answer, as you will put less heat into the material but your also going to lose your shielding gas coverage faster meaning the material has less time to cool before exposed.

Originally Posted by zapster

Unreal.

...zap!

It is unreal that a self proclaimed TIG god like yourself has nothing helpful to add to this, only vague mocking remarks.

[weldbead]

the attached foto is ms not ss,..if the color spectrum is different for ms than ss i apologize..but what is of interest is as this weld goes from right to left, look at the heat mark..where it goes to blue the heat mark is shorter. then as it goes back to gold and silver the heat is building up higher..??

[Supe]

The color difference has more to do with travel speed. You hesitate at the start of the weld as you form the molten pool prior to adding filler, so shielding is increased in that area. Same at the end of the weld where you stop to add your last few dabs of filler and then wait for post flow.

Heat tint on the base material will almost always protrude out more near edges. In the middle, heat can dissipate 360 degrees. Towards the edges, if the heat can't dissipate laterally as pictured above, it's going to travel in the other direction. Notice how the gradual accumulation of heat is linear on the top component from right to left, since the area for the heat to dissipate remains the same (no side edges).