The invention relates to a plastic corrugated pipe having a smooth inner wall and a corrugated outer wall, which corrugated pipe comprises a plurality of annular corrugation profiles, which are arranged adjacent to one another and are each symmetrical with respect to a centre plane that extends perpendicular to the centre axis of the pipe, each corrugation profile having a cylindrical wall part which is concentric with the centre axis of the pipe, and a wall part which is substantially arcuate in axial section and which extends from the cylindrical wall part, in such a manner that the cylindrical wall part and the arcuate wall part delimit an annular cavity, the inner surface of the cylindrical wall parts which adjoin one another forming the smooth inner wall of the pipe, and the outer surface of the arcuate wall parts which adjoin one another forming the corrugated outer wall.

A corrugated pipe of this type is known from WO 02/081957. In the known corrugated pipe, the arcuate wall part is formed by two straight wall parts which extend radially outwards from the cylindrical wall part, and a curved wall part which connects the two straight wall parts .

It is an object of the invention to provide an improved corrugated pipe.

This object is achieved by a plastic corrugated pipe of the type described in the preamble of claim 1, characterized in that the profile height of the corrugation profile is 6.0-8.5% of the internal diameter of the pipe, the pitch of the corrugation profile is 15-23% of the internal diameter of the pipe, and the width of the corrugation profile is 77-82% of the pitch.

In the corrugated pipe according to the invention, the corrugation profile is relatively low and wide compared to known corrugated pipes. This results in an expedient shape with the pipe on the one hand being sufficiently resistant to radial deformation without the pipe buckling, while on the other hand having a sufficient radial stiffness.

Preferably, the arcuate wall part has two straight wall parts which extend outwards from the cylindrical wall part, approximately perpendicular to the centre axis of the pipe, and a wall part in the form of a gable roof, which connects the two straight wall parts.

It is preferable for the straight wall parts to extend at an angle of 91-100° with respect to the centre axis of the pipe. In one specific embodiment, the straight wall parts extend at an angle of between 94-100° with respect to the centre axis of the pipe.

The roof-shaped wall part advantageously comprises two limbs which form an obtuse angle with one another.

The limbs of the roof-shaped wall part are advantageously at an angle of 7-15° with respect to the centre axis of the pipe, which prevents the roof-shaped wall part from buckling in the event of radial deformation of the pipe.

In a further expedient embodiment, a rounded corner with an inner radius which amounts to at least 0.5 times the wall thickness of the arcuate wall part is arranged at the transition between the straight wall parts and the limbs of the roof-shaped wall part, which improves the impact strength of the pipe.

The invention will be explained in more detail in the following description with reference to the drawing, in which: Fig. 1 shows a side view of a corrugated pipe part according to the invention, and Fig. 2 shows a cross section through a corrugation profile of a corrugated pipe according to the invention.

Fig. 1 shows a corrugated pipe part 1 which is formed by a plurality of annular corrugation profiles 2 which adjoin one another and are arranged behind one another and concentrically with the centre axis 3 of the pipe part 1. The pipe part 1 is preferably made from PP copolymers, but may also be made from other plastic material, such as for example PE or PVC.

Fig. 2 shows a cross section through a single annular corrugation profile 2. Reference numeral 3 once again denotes the centre axis. To simplify the illustration, only one half of the profile is shown. The pipe part 1 has an internal diameter which is denoted by ID in Fig. 2. It should be noted that the arrow denoted by ID in Fig. 2 represents only half the internal diameter, on account of the half illustration that has been selected. The pipe 1 may have an internal diameter ID of 200-800mm.

The annular corrugation profile 2 is symmetrical with respect to a centre plane, which is denoted by reference numeral 4 and extends perpendicular to the centre axis 3 of the pipe part 1. The corrugation profile 2 has a cylindrical wall part 5 which is concentric with the centre axis 3 of the pipe part 1. The cylindrical wall part 5 has a wall thickness E1 which is 0.60-0.90%, and preferably 0.60-0.80%, of the internal diameter ID of the pipe part 1, with a wall thickness E1 of approximately 0.65% of the internal diameter ID of the pipe part 1 being particularly preferred.

Furthermore, the profile 2 has a wall part 6 which is substantially arcuate, as seen in axial section, and extends from the cylindrical wall part 5. The wall thickness of in particular the said arcuate wall part of the pipe depends to a large extent on the radial stiffness required, in which context the materials properties (for example the modulus of elasticity) obviously also have an influence. For a pipe with a stiffness class 516, measured in accordance with ISO 9969:1994, the wall thickness of the arcuate wall part is approximately 0.60% of the internal diameter. For a stiffness class S8, it is approximately 0.65%, and for stiffness class S4 approximately 0.70%.

The cylindrical wall part 5 and the arcuate wall part 6 delimit an annular cavity 7, which is concentric with the centre axis 3. The inner surface 5a of the cylindrical wall parts 5 which adjoin one another form the smooth inner wall of the pipe. The .outer surface 6a of the arcuate wall parts 6 which adjoin one another form the corrugated outer wall ot the pipe, as can also De seen m .tig. i.

The corrugation profile 2 has a profile height H which is approximately 6.0-8.5% of the internal diameter ID of the pipe 1. The corrugation profile 2 has a pitch P which is approximately 15-23% of the internal diameter ID of the pipe 1. Furthermore, the corrugation profile 2 has a width W which is approximately 77-82% of the pitch P. In a corrugated pipe 1 with a corrugation profile 2 of this type, the corrugation profile 2 is relatively low and wide compared to known corrugated pipes. This results in an expedient shape, with the pipe on the one hand being sufficiently resistant to radial deformation without the pipe buckling, while on the other hand also having a sufficient radial stiffness.

Another advantage of the pipe having the said profile height H, pitch P and width W is that the impact strength is improved by the relatively wide corrugation profiles. Yet another advantage is the improved resistance to local deformation. On account of the relatively wide corrugations 2 and narrow spaces between them, the risk of stones and the like pressing against the relatively thin and vulnerable inner wall, i.e. the cylindrical wall parts 5, and causing damage there as a result of punctiform loads, during or after laying of the pipe, is low.

If pipe parts 1 of the type described are connected to one another by means of a pipe sleeve, a rubber ring is arranged in the valley between two profiles 2 in the vicinity of each pipe part end, in order to obtain a good closure and seal. In the corrugated pipe 1 according to the invention, it is advantageous for the distance between the profiles 2 to be relatively short, with the result that only narrow rubber rings are required to connect pipe parts 1. This saves material and is therefore less expensive.

The arcuate wall part 6 preferably has two straight wall parts 61, which extend outwards from the cylindrical wall part 5 approximately perpendicular, preferably at an angle α of 94-100°, with respect to the centre axis 3 of the pipe 1. Furthermore, the arcuate wall part 6 comprises a wall part 62 in the form of a gable roof, which connects the two straight wall parts 61. The gable-roof-shaped wall part 62 comprises two limbs 62a which form an obtuse angle with one another and are at an angle β, which is preferably approximately 7-15°, with respect to the centre axis of the pipe.

The transition between the straight wall parts 61 and the limbs 62a of the roof-shaped wall part 62 is preferably provided with a rounded corner with an inner radius R2 which is at least 0.5 times the wall thickness ET.

A corrugated pipe according to the invention can be produced by means of techniques which are known per se. The cylindrical inner pipe comprising the cylindrical wall parts 5 is produced by extrusion. The corrugated outer pipe comprising the arcuate wall parts 6 is produced, for example, by extruding a pipe, then heating a pipe part to a softening point of the pipe material. Then, the pipe part is surrounded by one or more die blocks with recesses in order to form the corrugations. A differential pressure is applied in the pipe part between the inside and the outside, so that the pipe wall is pressed into the recesses in the die blocks. Then, the corrugated outer pipe and the inner pipe can be fitted concentrically into one another at a temperature which is such that the inner pipe and outer pipe are bonded to one another.