Welding

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fredrosse
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Welding

Post by fredrosse » Sat Nov 18, 2017 2:29 pm

I consider myself a rank amateur compared to many professional welders I have seen, but have had reasonable success with Stick welding (SMAW) and MIG welding (GMAW).

Now I need to do some fancy TIG welding (GTAW) of 316L stainless steel, mostly making socket welds in 1" to 2" Schedule 40S pipe.

I need to buy the machine, and now have to learn to coordinate two hands and a foot at the same time, compared to only one hand movement for MIG and Stick welding. If anyone has practical experience about the process I would appreciate input.
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Re: Welding

Post by lostintime » Sat Nov 18, 2017 8:00 pm

Ive welded the CIP (clean in place) piping, heat exchanger piping, and product piping (which requires full sanitary weld ) at the plant I work at, all in seamless 316 tubing (.040"), as well as conveyors and work platforms out of 308 1/4" stock. If your not going to ever weld aluminum than a direct current machine is all you need. Iv found the foot pedal more trouble than its worth, as long as the material thickness is constant I prefer to just set the amperage and go. The down side of this is at the end of the bead it will leave a divot. With a alittle practice you can add an extra drop of filler rod right before lifting the arc off and it fills it in. Keep the the electrode sharp (use thorium not lanthium electrodes). If you dip the electrode in the pool (and you will alot when you learning) just stop and resharpen it. A dirty electrode makes the arc erratic, and contaminates the weld. Keep a dedicated grinding wheel for sharpening the electrode or dress the stone down before sharpening. If its been used on regular steel your welds will be contaminated and rust. If you are going to weld any thin material hold the electrode vertical while you sharpen it so any scratch marks go towards and end at the point. Do not use any steel wire brushes on stainless or it will rust. (3m makes a scotchbrite style buffing wheel that works great). In thin gauge match your filler rod diameter to your material thickness, in thicker gauges I often bunch 3 or 4 rods together to get a faster fill rate. Dont be stingy with argon. Get a good dual regulator because you have to also cover the back side of the weld with argon or it will burn. For piping I tape off the ends with blue painters tape (poke a couple hole in the end opposite the side you put the argon hose in) purge it than leave just enough flow to keep the alittle flow. As far as the welder, for sch. 40 id use a large cup to be able to keep enough argon flowing over the still hot bead without it coming out to fast that it blow hard on the spot you are working. 316 sticks together pretty well so you can use the pool to pull material across a gap. When your weld penitration is full you will see two little "eyes" spinning around each other in the center of the bead, if they are not there its not going all the way through the material.
Last edited by lostintime on Sun Nov 19, 2017 12:02 am, edited 1 time in total.
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lostintime
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Re: Welding

Post by lostintime » Sat Nov 18, 2017 8:10 pm

Forgot preweld cleaning, I use denatured alcohol first followed by fast evaporating contact cleaner. After its done(edit: the weld is done) buff it, then passivation with an acid cleaner or it will rust. And I'll reiterate again, any tool that has been used on regular steel will contaminate stainless and cause it to rust. And a general rule you can use a higher grade of stainless as filler but never lower or it will rust, but if 316L was called out over standard 316, id ask what rod to use.
Last edited by lostintime on Sun Nov 19, 2017 1:36 am, edited 1 time in total.
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Re: Welding

Post by lostintime » Sat Nov 18, 2017 8:23 pm

And dont breath the dust when sharpening electrodes (radioactive),have good ventilation while you weld or the vandium fumes will give you the shakes for the next two days, and wear long sleeves or the skin above your gloves will peel.
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Re: Welding

Post by lostintime » Sun Nov 19, 2017 1:33 am

Also dont fall for the whole "walking the cup" b.s. It does work, but in reality I've found resting my pinky nuckle against the part (or a rest)so my fingers are doing the movement instead of my arm gives FAR greater control and much better results. With proper heat and material control you just have to keep slowly moving the arc along and the bead lines are a natural result. It you are trying to force the bead lines (like in walking the cup) something is wtong.
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fredrosse
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Re: Welding

Post by fredrosse » Sun Nov 19, 2017 2:55 am

Thanks very much for this info. I know I will have lots of questions when I start practicing.
The weld procedure for this work allows GTAW and SMAW, but I thought the stick welding would probably burn thru with only 0.109 wall pipe.
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Re: Welding

Post by RGSP1 » Sun Nov 19, 2017 2:41 pm

I have been only a very sporadic user of TIG welding, but for some decades. We had an ancient power supply, and used pure Tungsten tips, but it it was for small stuff anyway, and they didn't need sharpening too often. We never sent cover gas to the back of the weld, and the back did therefore go blue, but that didn't matter for us, and may not for others.

Using the TIG torch is marginally more difficult than an acetylene flame, but in the same league, and it really only needs a bit of practice, like most welding. Note that I am NOT talking about structurally critical welds, which might well require more skill than I have at least, and more checking.
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Re: Welding

Post by cyberbadger » Sun Nov 19, 2017 7:08 pm

RGSP1 wrote:Using the TIG torch is marginally more difficult than an acetylene flame, but in the same league, and it really only needs a bit of practice, like most welding. Note that I am NOT talking about structurally critical welds, which might well require more skill than I have at least, and more checking.
Several times when I have gone to a welding supply for oxygen and acetylene they have suggested that if you have oxy/acetylene welding experience it should make learning TIG welding easier.

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