Originally Posted by knipknup
Only if you don't clean it. And make sure your welding is done in a food friendly manner - no funky solder.
Welding and soldering are distinctly different processes. Welding involves melting both the substrate metal and filler metal to produce a strong, contiguous, and largely homogenous seam. Soldering is the application of an alloy with a relatively low melting point to unmelted substrate metal, so that the bond is solely on the face of the substrate and is limited to the strength of the solder (which, in some cases, can be stronger than a weld, but usually not).
You will most likely be soldering your pipe. Be sure to use a lead free solder and flux meant for drinking water systems.
Should you decide to weld your copper pipe, be sure to use a respirator and pure copper filler...and practice a lot! The welds will look cooler than soldered joints, but it probably isn't worth the time/effort/equipment/cost/etc to do it that way.
Oh yeah, and to answer your original question...copper pipe will work just fine for your rig if you keep it clean. Always run hot water through the pipes after using them to transfer beer/wort, and run a mild vinegar solution through it from time to time to clean it.