TIG welding stainless steel? Investing in three areas may help
Welding stainless steel with gas tungsten arc welding (GTAW), also known as TIG, often becomes a delicate matter.
You don’t want to add too much heat to stainless steel, which generally is a more sensitive material to work with. As a result, the heat input and heating calculations are very important.
This is where weld travel speed comes into play. The faster you can travel while TIG welding stainless, the less time you spend welding on a part, which translates to less heat absorbing into the surrounding material.
Investing in smaller and portable inverter power sources, pulsing, and even argon/hydrogen shielding gas blends can help you optimize heat input, travel speed, and weld penetration—benefiting TIG welders and shop owners alike.
Inverter Power Sources and Portability
For many, working on stainless steel means working with piping and tubing at job sites such as chicken processing plants, vodka distilleries, microbreweries, pharmaceutical facilities, and others.
Much of the work now can be done in-house, oftentimes with larger welding equipment. Ultimately, though, most applications will require you to go to the job site where large transformer machines are not convenient due to the input power requirements and mobility logistics.
“First, they are extremely heavy,” said Andrew Pfaller, segment manager for Miller Electric. “But then, if you do find power, do you have the right connections? Do you have to relink the product? That often creates issues.”
Portable inverter power sources generally weigh less than 50 lbs.—significantly less than a transformer machine. “Like the size of a lunchbox,” Pfaller said. Most of them will be 150, 160, or 200 amps because fieldwork usually can be done with 200 amps or less.
“Typically, you can, as an individual, carry an inverter machine onto a job site by yourself without using a forklift or having someone help you lift it … if you can do that with one person instead of two, that will significantly impact your productivity and profitability,” he said.
Pulsing Gives Control, Reduces Arc Lag
Along with portability, inverter technology allows for pulsing at higher frequencies. A transformer-based power source typically gets 10 to 20 pulses per second. An inverter-based power source can achieve as many as 500 pulses per second; some even can reach 5,000 pulses per second.
Pfaller said anything higher than 100 pulses per second will give you greater directional control.
“If you’re trying to do a fillet weld or an inside corner joint or a T-K-Y connection like in pipe and tube, that allows you to point the arc and weld where you intend,” he said.
“In sanitary piping and tubing—which is used a lot in the food and beverage industry and dairy production—it’s all thin-wall stainless steel with relatively low amps; you don’t have as much force in the arc from the amperage. You need to supplement that with the arc stability pulsing brings.”
Using a pulse helps reduce “arc lag,” which is when the welding arc lags behind wherever the electrode is pointed and where the puddle actually forms.
“It may be a poor way to describe it, but it is almost like being intoxicated. Your brain is thinking one thing, but your body is lagging behind with its response,” Pfaller said. “The material in those nickel alloys behaves similarly in that it has a slow response to your inputs.
“Using a pulse can cause puddle agitation, which reduces the amount of lag and puddle delay. So, what does that mean for somebody? It can mean better weld quality because now the weld is going where they want it to. They can have faster travel speeds because now they’re not waiting for that puddle to catch up.”
Pulsing reduces the weld’s heat input, which can reduce the amount of distortion. As a rule of thumb, steels shrink about 10% when they solidify, said Pfaller.
“If you have a welding joint and you’re doing a much larger welding puddle than what’s needed, that puddle shrinks, and when it solidifies it causes excess distortion,” he said. “That distortion often results in some form of rework or straightening process that wasn’t accounted for. Companies spend a lot of time fixing or straightening things after welding and before they can do subsequent operations.”
Is Argon/Hydrogen Mix Worth a Try?
Historically, TIG welders use argon as their shielding gas when working with stainless steel. However, in certain applications, like welding thin-wall tubing, some have switched to a low-percentage hydrogen blend. In this scenario, about 1% to 2% hydrogen is blended with argon.
Pfaller said he’s seen growing use of the argon/hydrogen shielding gas blend. This mixture creates more heat to change the weld penetration profile.
“People doing sanitary tubing or thin-wall tube will use a square butt joint rather than put a bevel on the pipe. They then use a hydrogen-blended shielding gas and get additional penetration to essentially eliminate that joint prep,” he said.
This blend should only be used with stainless steel alloys, he added.
Unlike helium—which faces a supply shortage at this time—hydrogen and argon supplies are not a concern given their relative abundance in the atmosphere.
Some businesses have opted to blend it on their own, Pfaller said. He cautioned shops to think this over carefully given the blend’s flammability in higher concentrations.
“Those investigating mixing it themselves need to take the necessary precautions to make sure they’re maintaining a very low percentage in the shielding gas blend,” he said. “It can create safety concerns, and precautions that need to be taken if blending it themselves versus bringing in a premixed blend from a gas supplier. That’s something their shielding gas supplier can provide some guidance and governance on.”
Long-term Operations Savings
Ultimately, making changes in these areas will reap more benefits financially than looking for savings in consumables budgets or TIG torch cup replacements, Pfaller said.
Many of the people Pfaller talks to don’t make changes because welding accounts for about 10% of their shops’ operations. If welding speed improves by 10%, that amounts to about 1% savings in total operations.
The benefits that come when switching to inverter-based power sources and pulsing include eliminating nonvalue-added work, using a more aggressive joint profile, eliminating bevels on pipes, and achieving full penetration on a square butt joint.
“That welding prep time and post-weld rework and operations are where a vast majority of a company’s time is spent,” Pfaller said.
“Utilizing things such as DC pulsing, now you can reduce or essentially eliminate some of those other welding-related operations. If you can eliminate those, now you’re not just eliminating 1%, you’re eliminating 10, 20, 30% of that company’s pre- and post-weld operations,” he said.