So, I have an upright compressor (pictured below) that has a metal pipe leading from the motor to the tank. I had my compressor running and an air line was resting up against this tube and it has heated up the plastic enough to stink up my garage (It didn't melt it thankfully). I touched it and it burned my fingers like touching cookware. I assume it's normal operation, and I assume (But could be wrong) that that tube is how compressed air gets into the tank, but I don't understand why it's so hot. An explanation would be greatly appreciated.
Unfortunately, I couldn't find a picture of the compressor from the backside showing the tube, but this is the compressor. The tube leads from the rear of the plastic housing to the top of the tank.