Two-layer conveying pipe. The wear-resistant inner pipe is uniformly through-hardened to 63HRC over its entire length. The outer pipe is pressure bearing. The male-female geometry of the weld-end surfaces centers the pipe and seals it tightly. O-rings are used as sealing elements. Particularly suitable for GRP “High performance plastics” due to the tight tolerances and after additional treatments of internal surfaces. Used to merge two conveying streams.