Hi Dave,
You have asked some very pertinent questions.First of all, before you consider ordering something from U.S. Alloys, I would like to have a phone conversation with you so I can ask some questions about your application. I like to get all the facts first. Send me an e-mail if that's the way you wish to proceed. In regard to your first question, a preheat is most likely not required. If you make this repair with an oxy/fuel torch, preheat is a given. In regard to your second question, it depends on the type of silver we are talking about. Many so called silver solders actually contain no silver at all. A true silver solder ( such as my #1210fc) is up to 56% percent silver with a bond temp that would define the alloy as a brazing rod and with a tensile strength of 85,000 PSI. For example, you can immediately notice the difference between a 40% alloy and a 56% alloy when in use. The biggest question you have raised has to do with the existing deposit on the lines. If it has been soldered as an OEM part, the easiest way to effect the repair will be with a compatible material. A high content silver alloy may not be what was used. Also, a high content silver alloy would be unsuitable for repairing holes because it flows so thin that it would be impossible to keep it out of the line. That particular alloy will even flow straight up! Steve
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