`Florida high-rise copper-plated stainless steel water piping failure`

Copper was expensive. When copper got even more expensive in the 1970s, Allegheny Ludlum Steel said, stainless steel is very good and we can make it thin wall and cheaper, but we have to have something that the plumber can solder to. So that's another material property in the material selection. You can't solder to titanium. It's got this protective oxide. There is no flux that will eat away the titanium oxide. So you can't solder to a titanium pipe. Stainless steel has a chromium oxide; you can solder it, but you have to use pretty aggressive chlorides which can pit the stainless steel. So they decided we'll just plate the copper — put copper plate on the outside, and now you can solder to it just like you do a copper pipe.