Volume 5, Number 2
April 2006
Q. I see aluminum tube welds with lots of porosity both with X-ray and penetrant. Is this normal? What causes these indications to be so relevant? Is it possible to have a porosity free aluminum tube weld these days? Thanks for any advice you can return. R.M.
A. Porosity results when gas bubbles are trapped in the weld metal as it solidifies, resulting in a loss of wall thickness at that spot. A good weld, aluminum or otherwise, should not contain unacceptable amounts of porosity, and porosity-free aluminum welds are quite common provided proper welding techniques are used. These will include properly precleaned base material, adequate shielding during the welding process, etc. On pipe and tube welds, back-purging may also be necessary to prevent porosity from forming at the root of the weld before the root gap is closed.
All of these measures should be described in the welding procedure and if you are finding large amounts of porosity in your welds, you may want to review and revise the welding procedure as necessary. You might also check for applicable welding standards (ASTM, AWS, ASME, etc.) to see if they can provide guidance on this problem. TNT
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