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Welding Talk – Gas Purging

Have you been trying pipe welding with stainless steel for the first time and noticed unwanted discolouring due to oxygen contamination inside your weld? Or maybe you’ve welded a vehicle exhaust and seen the same effect. Perhaps gas purging could have helped the quality of your weld. Read on to learn more…

When you need to protect two sides of a weld from oxygen contamination, gas purging often holds the key. Of course, there’s the gas purging you might face as a hobby welder or small commercial welding operation, then there’s the gas purging you find in high-end welding, way up in the welding stratosphere above where we – maybe you too – work. At that level, we’re into super-specialised techniques such as argon-bath welding. It’s the work, with stainless steel, titanium and exotics such as Inconel, using specialised argon-helium mixes and strictly-certified welding processes, that takes place at the high-end of advanced aerospace and F1 engineering. Interesting though it is, we’re looking at something much more mundane – but equally important for welders like us.

Gas purging for pro and amateur TIG welders

What we’re focusing on this week is basic argon gas purging as it affects DIY welders or smaller professional welding shops. Maybe, as our lead-in suggests, you’ve had a cracked weld on a piece of architectural metalwork, or a ‘crunchy’ gas-flow-inhibiting weld inside a stainless motorcycle exhaust. Theoretically, though we don’t recommend it, you could MIG weld stainless steel. More likely, however, you’ll be TIG welding. In our experience, most of the specialist-metal welding that benefits from gas purging is being done with the TIG process.

Why gas purging is important?

Before we get into the in's and out's of gas purging, we must say that weld contamination, maybe in the form of ‘sooty’ welds, is never down to the welding machine itself. Instead, experience shows that gas contamination, interaction with non-purged air and other causes are usually responsible. Often, particularly where front and back of a weld are equally exposed to atmosphere, or where the inside of tubular fabrications contain the back of a weld, gas purging makes a huge difference to weld quality. Fortunately, it’s not as hard as you might imagine…

As usual, set-up matters…

So you’ve decided that your welding job will benefit from gas purging. What next? First, as ever, all the usual advice about planning, machine and material set-up, choosing the right process, ensuring a large enough gas pocket, and using the right consumables, applies.

Displace contaminating oxygen

You’ll have worked out that material at the back or inside of a weld will be exposed to potential oxygen contamination. To get around this, you (perhaps helped by a colleague) need to displace the air – not just around the weld pool, but on the back of the weld.

You do this with a second flow of pure argon, ideally created with a second gas hose leading from your regulator. And because you may need to vary the primary (front of weld) and secondary (back of weld) gas flow, we recommend fitting dual argon flow meters downstream of a double-outlet gas valve Y piece (or ‘Y-splitter’). Of course, the splitter itself is downstream from the gas regulator.

Why we recommend two flow meters

Why would you need to vary the two gas flows? What if you’re temporarily sealing the inside of a pipe during welding? First, you’ll displace oxygen with a higher gas flow before temporarily sealing the end of the tube. Then you’ll turn the gas down to maintain purging. Similarly, you might want one gas setting at your electrode tip, while your assistant follows along the back of the weld with the secondary argon jet. Trust us, though it might be tempting to put a single flow meter upstream of your Y-splitter, it’s not recommended.

Let’s talk gas purging

The specific welding task and the metals you’re working with will decide the settings you use. All the usual guidance sources apply – including talking with our experienced team.

So there you have it; in the time it takes to enjoy a coffee, the basics of gas purging as it applies to so many pro- and amateur welders. As with welding in general, the principles are simple but mastery demands good information, technique, the right welding equipment and plenty of practice.

Call us for advice

With decades’ experience in welding, there’s not much our team hasn’t seen. Naturally, that includes gas purging and accessories such as hoses, gas regulators and flow meters.

If you’ve run into unwanted oxygen contamination while welding materials such as stainless steel – or you want to avoid problems – gas purging may help. As usual, the R-Tech team is a great source of unbiased advice on this or any other aspect of welding.

Send us an email or call us for a chat!

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