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Practical TIG Welding: Stainless Steel

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Stainless Steel


00:00 - Stainless steel is used extensively in motorsports for exhaust system manufacturing as well as a lot of smaller parts like fittings and fluid supply systems where corrosion prevention is a priority.
00:12 Stainless is a great material to weld but is more reactive than mild steel and chromoly so it's going to require more shielding gas to prevent a reaction with the atmosphere.
00:22 To prepare your material, use scotch brite to clean the surface then wipe the weld area and filler rod with acetone to remove any oils or contaminants.
00:30 Stainless steels have a low thermal conductivity and that means they require around 10% less amps than mild steel.
00:38 Heat sinks are also important to avoid warping on thin parts.
00:41 Consider clamping aluminium blocks to the back side of your parts if you're going to be running long flat welds.
00:48 When you're working with stainless steel tubing or tanks you should be sealing and purging the back side of the weld as well.
00:54 This requires argon to be fed into the lower portion of the tank or pipe to ensure that atmospheric air is completely removed prior to welding.
01:02 As a guide, you can approximate the volume of the part you're welding then add argon at around 12 litres per minute for 30 seconds per litre of capacity of the part.
01:12 The flow rate can then be reduced to 8 litres per minute for the duration of welding.
01:16 Make sure that the tube is vented in the opposite end of the purge inlet to ensure that pressure doesn't build up as the weld is completed.
01:24 Once welded, you should see a shiny smooth weld seam on the inside of the joint.
01:29 If the back of the weld has a coarse, rough, dark crater like appearance then this indicates that there's still contamination from ambient air occurring.
01:37 You can head to the purging module in the practical skills section for a more detailed look at this process.
01:43 Employing pulse settings with low frequency switching of around 1-4 Hz on stainless can really help with the weld appearance and reduce the heat applied to the part.
01:53 Stainless also benefits from a very small focused arc and it's absolutely imperative that we freshly sharpen our tungsten for stainless TIG welding.
02:02 When it comes to technique, welding stainless steel can get interesting because if the part isn't structural and your fit up is close to perfect, you may not need filler rod for the weld at all.
02:13 Fusion welding, which we've covered in detail in the practical skills section can be successfully used on stainless steel to create small intricate welds but if filler rod is to be used, try to weld in a uniform motion using your pulse controls to time the inclusion of the rod.
02:30 Keep a very close eye on the weld pool because it can burn a hole very quickly if the amperage is set too high.
02:37 A good stainless weld should be shiny with a colouring between silver, straw, through to blue purple, depending on the application.
02:44 With stainless being a reasonably reactive metal, we want to pay special attention to shielding gas coverage.
02:51 If the weld starts to look dull grey or even have a sugar like texture, this is a clear indication of inadequate gas coverage.
02:58 Sugaring often occurs on the back side of the weld if the part hasn't been purged.
03:02 It's worth mentioning that the varying colours on stainless welds indicate how much oxidising has occurred.
03:10 This affects the corrosion resistant properties of the stainless.
03:13 Anything beyond a blue colour indicates the risk of the weld rusting in extreme environments.
03:19 This might be acceptable for the application if aesthetics are more important.
03:24 These oxide colours can be removed using scotch brite which renews the corrosion properties.
03:29 In the resources section of the course, you'll find a PDF that lists baselines for all settings when working with stainless steel.

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