pipe extrusion line According to one aspect of the present invention, a roll assembly for guiding a pipe in a pipe extrusion line for producing pipes of different diameter, includes a bracket, a roll supported by the bracket, and an adjustment device for automatically positioning the roll in vertical direction in dependence on a weight load upon the roll. The present invention resolves prior art problems by so constructing a roll as to adjust its vertical position in dependence on the weight load acting on the roll. Hereby, the invention is based on the recognition that pipes of greater diameter normally have a greater weight per meter. Thus, when the roll is loaded by a pipe of greater weight, and thus normally also of greater diameter, the roll moves further downwards than would be the case, when the weight load on the roll is smaller as a result of a smaller pipe and thus of smaller weight. The roll is rotatably mounted on an axle which is supported indirectly or directly by an elastic element that forms the adjustment device. A plurality of materials and devices known per se may be used as elastic element, such as, e.g., rubber-like elements. Currently preferred is the use of a spring, in particular a spiral spring, as elastic element, for movably supporting the axle so as to allow the roll to move downwards as a load on the roll increases. Suitably, the spiral spring has a spring hardness which is suited to a weight per meter range of the pipe which range correlates with the dimension range. The rolls may also be constructed in such a way as to laterally support also the smallest pipes to be produced. Such pipes are preferably arranged in the area of the vacuum tank. The subsequent spray baths may use roll geometries which are configured in the form of a double-V-block so that the pipe is guided also in this case always on both rear sides. According to another aspect of the present invention, a pipe extrusion line for producing pipes with different diameter includes an extruder for plasticizing a starting material to produce a melt strand, an adjustable calibration device sizing the melt strand to shape for forming a molten tube, a cooling device for cooling the tube, and a roll assembly for guiding the tube during advance through the calibration device and the cooling device, wherein the roll assembly includes a plurality of rolls arranged behind one another in a travel direction and constructed to have at least two different roll geometries, and an adjustment device for automatically positioning the rolls in vertical direction in dependence on a diameter of a pipe being produced. By providing rolls of varying roll geometries, different support functions can be realized and varying support lines can be provided, for example a support of the pipe in the bottom area and various side areas. For example, one of the rolls may have a first roll geometry to conform to a maximum radius of a pipe being produced, and another one of the rolls may have a second geometry for lateral support of a smallest pipe to be produced. Pipe extrusion lines are generally known. The production of plastic pipes involves initial melting of a plastic starting material in an extruder and discharge via a pipe die. The exiting thermoplastic molten tube from the pipe die is cooled under shape constraint and calibrated. Calibration is of great importance as far as pipe dimensions and tensions in the pipe wall are concerned. Plastic pipes are calibrated predominantly on the outside, whereby a vacuum calibration device is typically employed. The still soft molten tube is drawn shortly after discharge from the die through a calibrator which is mounted in the vacuum tank. This calibrator can be configured as sleeve-type calibrator or disk-type calibrator depending on the thermoplastic material. In and following the calibration path, the extruded pipes must be cooled down to such a degree as to be sufficiently stable in shape for subsequent loads (for example take-off device, winder). Cooling of the pipes may hereby be carried out in tanks with water baths or spray nozzles. According to one aspect of the present invention, a roll assembly for guiding a pipe in a pipe extrusion line manufacturer for producing pipes of different diameter, includes a bracket, a roll supported by the bracket, and an adjustment device for automatically positioning the roll in vertical direction in dependence on a weight load upon the roll.