Does star-san dissolve silver solder?
I wanted a thermowell for my corny keg so I bought a Sta-Brite silver solder kit as recommended in the big silver soldering thread. I soldered a stainless-steel screw onto the end of the dip tube so that it would still fit down into the post boss on the keg.
I tested the solder by blowing into the top in with the rubber-tipped blowgun for my air compressor, putting 100PSI into the end while looking for bubbles with the soldered end in a glass of water. None.
I then filled the keg with a weak star-san solution and put the thermowell in it for about 5 hours. When I took the thermowell out of the keg and turned it upside down, water poured out! It was completely full of water, even though I had just tested it with 100PSI compressed air, and it was under no pressure in the keg...just what, 18 inches of water or something (1/2psi according to google). I was able to grab the screw that I had soldered to the end with a rag and yank it off with my bare hands.
The only thing I can think is that the star-san attacked the solder. I know that star-san uses phosphoric acid. Phosphoric acid is used as a soldering flux for soldering stainless steel. Is there something about star-san that attacks or weakens solder joins?