When mounting a thin-walled tubular in an internal upset drillpipe and fixating it in the tool joints, it is possible to create an annular volume between the drillpipe wall and the inner liner tube. This created space can serve for various duties like placing measuring equipment like strain gauges for example, electronics and sensors as well as insulation material or telemetry and power supply lines. For the success of these applications it is absolutely necessary that the annular volume is sealed against the drilling mud that is pumped down inside the drillstring. The target of this thesis project now is to determine and investigate the tightness and integrity of the inner liner sealing assemblies within 5in, 19,5lb/ft, G105 internal-external upset drillpipes. Therefore various inner pressure testing facilities were designed, layouted and constructed in order to be able to pressurize the sealing components of the liner assembly. The main test bed is in fact a model of a drillpipe excluding the connectors and shorter in length, but having the same inner shape and diameters. Having a liner tube installed and using the proposed sealing assemblies it is possible to mount the desired equipment in the annular volume (filler material, data lines...). By pressurizing the test cell to 700bar using a hydraulic pump, leakages of the metal sealing or a failure of the liner tube itself can be detected by observing a pressure drop.