12 to 1400 degree melting point. I doubt that your exhaust gets anywhere near that hot, SilverBear.
I'd need to see what solder you used to tell you what went wrong with your pipe. My guess is that it was not actually 'silver solder' which is technically called an brazing alloy, but some less expensive subsitute marketed under the name, silver solder.
There is a lot of misunderstanding regarding soldering/welding/brazing. There are terms used that does not always accurately describe the product.
The type I pictured above would not be effected by any exhaust system unless maybe you're talking about the space shuttle.