When I bought my truck it already had a Flowmaster exhaust on it. Over the years it's rusted out so I bought a new Flowmaster set to replace it. The one thing that worries me is the pipe that comes from the factory connects to a pipe in the kit that connects to the muffler. Well, since the kit is so old I think the factory pipe has rust-welded itself to the old Flowmaster pipe. So my questin is, how do I remove that Flowmaster to factory weld pipe? Do I try to grind off the Flowmaster pipe on the outside until it's thin enough I can get it off the factory pipe?

 

short answer is yes, you'll need to grind off as much weld as possible If you want to "save" as much pipe as possible. Providing the pipe is still solid enough.
But...odds are you'll have enough "movement" in the hangers and such that you can just saw it off right behind the previous weld and still get things put back together. A sawzall works well, or go old school and use a hacksaw. Attach a hose clamp around the pipe where you need to cut and use it for a guild to help keep things straight.

Most muffler shops can make up any kind of connecting pipe you need, if you need one. Just tell them the O.D. & I.D. and length, and flare one end to slip over the up stream side.

There are on line places that you can but exhaust pipe too if you don't want to involve the locals

 

Cut above it if that will leave you Enough pipe. Then get a hold of Eric at classic chambered exhaust and add a 3030 SB. I just had one put on this week. Sounds awesome.