Hello diverdileo, you ask some doosies for questions. Once again there are a "large" number of variables that could be considered to properly answer your question. A large number of autogeneous welds are made with the GTAW process, food service and medical are prime examples. Small, smooth, autogeneous welds are often used for the cosmetic as well as non-bacterial harboring benefits. Other materials don't fair so well when they are welded autogeneously due to centerline cracking issues and others, an example might include welding 6061-T6 aluminum to itself without filler(that's the quick description, there are plenty of variables there as well). In some instances there might be certain metallurgical issues that could compromise either the corrosion resistance of particular materials or the strength, heat input from welding might be an issue. Since GTAW tends to have a higher rate of dilution than other welding processes, using it for "washing" a weld might compromise the weld by increasing this dilution. I am sure others could include a great amount of additional points, so I'll let them do so for now. Best regards, Allan

it can be used for tempering, or distortion repair via balanced heat input. As mentioned notch and cracks to hide bacteria is another common use for washing beads.  Of course it adds heat input into the metal so that should be a consideration.  It is sometimes used to hide the appearance of heat tinting which can be a big no no.

It's just an autogenous weld over a previous pass, you can use it for whatever need you have.