A preheating arrangement for a welding device having an upper tool mounted to an upper support and a lower tool mounted to a lower support, wherein the upper and the lower support are movable relative to each other between an initial position and a welding position, and the preheating arrangement comprises: a. a preheating device defining a first plane by means of a first centerline extending along a first axis X and a second centerline extending along a second axis Y being perpendicular to the first axis X and b the preheating device has a first side with a first preheating structure and an opposite second side with a second preheating structure, wherein c. the first preheating structure is asymmetric with respect to the first and/or the second centerline so that the respective axis is an axis of asymmetry, and d. the second preheating structure corresponds to the first preheating structure and is oriented like the first preheating structure such that, when viewed along a third axis Z perpendicular to the first plane, the first and the second preheating structure are arranged one above the other, characterized in that e. the preheating arrangement comprises further a first rotating means for rotating the preheating device between a first position and a second position such that the preheating structures (14, 18) in the first position have a first orientation and in the second position a second orientation e1. in which they are rotated around the axis of asymmetry by 180° compared to the first orientation or e2. in which they are rotated by an angle α in the range of 0° < α < 360°, preferably 90° ≤ α ≤ 270° and particularly preferred α = 180° around the third axis Z compared to the first orientation. a. a preheating device defining a first plane by means of a first centerline extending along a first axis X and a second centerline extending along a second axis Y being perpendicular to the first axis X and b the preheating device has a first side with a first preheating structure and an opposite second side with a second preheating structure, wherein c. the first preheating structure is asymmetric with respect to the first and/or the second centerline so that the respective axis is an axis of asymmetry, and d. the second preheating structure corresponds to the first preheating structure and is oriented like the first preheating structure such that, when viewed along a third axis Z perpendicular to the first plane, the first and the second preheating structure are arranged one above the other, characterized in that e. the preheating arrangement comprises further a first rotating means for rotating the preheating device between a first position and a second position such that the preheating structures (14, 18) in the first position have a first orientation and in the second position a second orientation e1. in which they are rotated around the axis of asymmetry by 180° compared to the first orientation or e2. in which they are rotated by an angle α in the range of 0° < α < 360°, preferably 90° ≤ α ≤ 270° and particularly preferred α = 180° around the third axis Z compared to the first orientation. e1. in which they are rotated around the axis of asymmetry by 180° compared to the first orientation or e2. in which they are rotated by an angle α in the range of 0° < α < 360°, preferably 90° ≤ α ≤ 270° and particularly preferred α = 180° around the third axis Z compared to the first orientation.