Pipe reduction piece made from plastic material

A pipe assembly comprising:

• at least two pipes each having an end section, a first pipe having a greater inner diameter than a second pipe;
• a plastic pipe reducer having an interior volume that accommodates fluid flow, the reducer having a first section and a second section with inner walls adjoining one another in a transitional region in a flush manner, with the inner wall of the first section delimiting a first cylindrically embodied partial volume of the interior volume, and with the inner wall of the second section delimiting a second partial volume of the interior volume, said second partial volume having a cross-section that decreases in the direction of the first partial volume, wherein the first section and the second section of the pipe reducer are essentially rotationally symmetric around the longitudinal axis of the reducer, wherein the first section of the reducer has an outer wall that defines a step, wherein a relief groove is formed in the step;
• and
• first and second connecting elements, the first connecting element having one end connected to the end section of the first pipe and the other end connected to the reducer, the second connecting element having one end connected to the end section of the second pipe and the other end connected to the reducer so as to abut the step, the connecting elements connecting the first and second pipes to the reducer, wherein the first connecting element includes heating wires therein and is integrally joined to the end section of the first pipe and to the reducer by electrofusion, and wherein the second connecting element includes heating wires therein and is integrally joined to the end section of the second and to the reducer by electrofusion.