anyone who is saying welding SS is difficult is just plain wrong .. I have used a $60 Ebay bough spot welder to make pipes from anything between .006 - .01 SS... After a few practice welds and getting used to the flick of the switch to get the weld just right, it was a piece of cake. Making a 2 wall straight pipe is very straight forward and easy ... The first pipe i made was a bifurcated and curved pipe for a turbine heli. The biggest challenge was getting the geometries of the pieces right so as to end up with the proper shape after bending and welding into place ...
here is an example of a spot welder that can be easily used. The tongs can be bent and formed to diferent shapes if needed so as to fit into tight spaces for unique pipes if needed.
http://cgi.ebay.com/115-V-ELECTRIC-S...QQcmdZViewItem
# 220067487969 if the link does not show ...
Voy