How to achieve optimum weld quality on stainless tube
Posted by Brandon Arnot on January 19, 2021
Achieving quality welds on stainless tube
Whether welding waste outlets in an abattoir, or welding class 100 pharmaceutical tube in a cleanroom, quality is always a number 1 priority.
Several factors can be challenging to any tube welder, including:
Access. Tight access around tube can prevent repeatable and quality welds. Awkward positions and poor ability to see the weld can lead to problems, even for the most skilled operators.
Wind and air turbulence. TIG welding tube outdoors can prove to be very difficult. The argon gas shielding the weld pool can easily be disturbed, leading to common problems such as porosity and tungsten inclusions to the weld.
Fatigue. Welding tubes, especially in position, is hard on the body. Constantly changing position to get the best desired results can quickly wear out operators, causing mental and physical fatigue. As a result, quality can be impacted.
Cleanliness. Tube cleanliness is an often-overlooked challenge that tube welders face. A small amount of contaminant on the surface of tube ready to be welded can lead to far reaching effects.
To minimise the possibility of quality issues whilst tube welding, here are some simple tips.
Use quality tube. Always inspect the quality of tube upon receiving. Is it as per the specs? Any discolouration inside? Sample welds are OK on this tube?
Quality cuts. Tube needs to be cut square. Use either an orbital tube cutting machine and where possible, face tube with a tube squaring machine. This drastically improves both fit-up and weld quality.
Clean before tacking. Ensure all burrs are finely filed off, and any impurities are removed from the tube. Spraying acetone on the surface inside and out and wiping off with a lint free rag will minimise any residue on the surface
Good fit-up is king. Your weld will only be as good as your fit-up. Use tacking clamps to ensure you have tight fit-up and good alignment. Use a tacking mode on your welder, or just do small surface tacks. The best tacks do not penetrate through the tube. The most common problems arise from tacks that have penetrated through the material and remain after welding.
Purge correctly. Use dedicated purge bungs and monitor your purge pressure through the tube. Always check that there is no oxygen left inside the tube, using a purge monitor.
Ensure adequate gas shielding. Make sure your argon gas through the TIG torch adequately covers the weld pool. Wherever possible, use an enclosed orbital welding machine if having to weld outside.
Inspect welds upon completion. Use a borescope to check your weld once finished. It’s what’s inside that counts!
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