Riddle

Because you just learned how to weld and you are looking for any excuse to use your welding equipment? (That is certainly the genesis of many of my woodworking projects -- a new toy demands a project. I now have a lot of ugly band saw boxes.)

Anyway -- I will guess that the pipe has something to do with how you carry the bike on your TC. Maybe an anti-wiggle fitting, so that the bike does not not vibrate while on the carrying rack, which could stress out the drawbar in your hitch receiver.