Single-layer, internally hardened pipe system for hydraulic and pneumatic conveying of slightly abrasive media. The pipes and elbows are internally hardened up to 45 HRC. The hardness decreases linearly from the inside to the outside. In addition to hardened elbows, manganese cast elbows are also used in some cases. Special tube shapes on request. In comparison, the ESSER 400 series has a service life of 2 to 3 times that of conventional steel pipes.