Method of welding a component part to a plastic fuel tank

A method of welding a component part provided with a peripheral wall including an inner HC barrier layer and an outer weldable layer and defining an annular lower end surface exposing end surfaces of the inner HC barrier layer and the outer weldable layer thereof to a tank main body of a plastic fuel tank of a laminated structure including an inner layer, a HC barrier layer, a recycled material layer made of recycled material and an outer weldable layer, in that order, the method comprising the steps of:

• forming an annular upright wall in a wall of the tank main body, the annular upright wall including an inner peripheral surface defining an opening of the tank main body and an annular top surface exposing end surfaces of at least the HC barrier layer and the outer weldable layer;
• and
• welding the end surface of the weldable layer of the component part to an outer surface of the weldable layer of the tank main body surrounding the annular upright wall to form a first welded part and to the end surface of the weldable layer of the tank main body exposed at the top surface of the annular upright wall to form a second welded part while the HC barrier layers exposed at the top surface of the annular upright wall and the lower end surface of the peripheral wall of the component part, respectively, are kept substantially aligned with each other.