Two-layer conveying pipe with a wear-resistant inner pipe and a pressure-bearing outer pipe. The inner pipe is uniformly through-hardened over its entire length. The wear layer has a hardness of 63 HRC. The thick-walled pipes can also be used in very short lengths in neuralgic wear points of the mast. The ESSER TWIN 700 series has been used for decades on a wide variety of construction projects worldwide.