Careful with sandblasting and welding. . .make sure that you are using a blasting media that will not introduce contaminants into the weld or make sure that there isn't any blasting media embedded in the base metal. . .your welds will end up contaminated and will be the starting point/catalyst for cracking and porosity. . .
Just out of curiosity, what happens if you dont clean DOM tubing before welding? Is it that big of a deal?