We generally weld floats for level control inside of the gas tank or other liquid areas or mechanical pressure switches. Here is an example of a good weld. I could change the speed on this part all over the place and it would not change the color. This particular part is tested several times per year by an international plumbing society. It has looked psychedelic since we started making it in 1973. We have had zero returns for porosity or failure through the weld. It is made from 304L.
I weld and design with pretty much exclusively stainless steel alloys (303, 304, 316, 450, Hastelloy, etc).