I suppose you're talking about LINING (not exactly welding) steel with glass, like glass lined piping and vessels for chemical service. If so, your's not an easy question to answer. There are only two companies in the world that make that kind of equipment, which means that it's quite a sophisticated technology. Those companies are Pfaudler in the USA and De Dietrich in France. Of course, they won't tell you a word about how they do it. Sorry for not having been of help.
Giovanni S. Crisi
Sao Paulo - Brazil