Filler tube and manufacturing process for the same

A filler tube to be welded to a fuel tank at an opening thereof, and made of thermoplastic resin;

• prior to being welded, the filler tube comprising:
• a non-bellows cylindrical base with a total thickness of from 2 to 4 mm;
• a bellows with a total thickness of from 0.5 to 3 mm;
• a flange having a total thickness of from 3.5 to 5 mm, and including an end face to be welded to the fuel tank;
• and
• a non-bellows-shaped heavy-thickness cylinder with a total thickness of from 4 to 6 mm;
• the base, the bellows and the flange including:
• an inner layer formed so as to have a thickness accounting for from 40 to 60% of the total thicknesses, and formed of high-density polyethylene (or HDPE) serving as a major constituent thereof;
• an intermediate layer arranged on an outer peripheral side of the inner layer, and exhibiting fuel-permeation resistance property;
• an outer layer arranged on an outer peripheral side of the intermediate layer, and protecting the intermediate layer;
• and
• the flange protrudes outward radially from an end of the heavy-thickness cylinder in one of sides thereof facing the fuel tank.