The fragment is "probably a wastewater pipe," a police spokesman said.
Authorities had been planning to defuse the supposed bomb and clear the main train station at 8:30 am. Residents and hotel guests within a 325-metre radius of the pipe's location would also have been affected.
Bomb disposal experts were due to start work at 11 am, but investigations prior to the operation helped the team determine that the object in question was not a bomb after all.
Police said the pipe's location had not been noted in any of the ground plans of the area around the station.