As the energy carrier of the future, hydrogen will make a decisive contribution to sustainable large-scale energy supply, with transportation based on long-distance transmission gas pipeline grids. Previous investigations of the general material compatibility show that the currently applied low-alloyed pipe steels are generally suitable for hydrogen pipelines under normal service conditions. Indeed, this cannot be directly transferred to the case of repair welding. For technical and economic reasons, welding work will typically be carried out on "in-service" hydrogen pipelines during operation under continuous pressure and gas flow. In that connection, concepts like the so-called "hot tapping" and "stoppling" are well established in the natural gas (NG) grids and crude oil transportation. In the case of the hot tapping, a pressurized pipeline is drilled by flanging a sealed, pressure-tight system consisting of a shut-off valve and drilling device. To do this, so-called sleeves (made from preformed cylindric half-shells) must be welded by longitudinal seams and then welded to the product-transporting pipeline with girth welds. Preheating temperatures of approx. 100 °C must be maintained for the majority of manual metal arc (MMA) welding and 250 °C for the interpass temperature in case of multi-pass welding. Special focus is placed on thin-walled pipelines, as the austenitizing temperature on the inside of the pipeline is exceeded when welding the girth welds. As a result, a significantly higher hydrogen absorption into the pipeline steel is assumed, with the possible degradation of the mechanical properties or crack formation. Due to the long welding and cooling time, the pipeline steel is  exposed to temperatures of the mentioned 250 °C sometimes for hours. In addition to classic "embrittlement", so-called high-temperature hydrogen attack may therefore also need to be considered. This study provides an insight into the transferability of established concepts from the NG grid technology for repair welding. The possibilities and limitations of current test concepts and their further development are shown. This includes the necessisity for the development for suitable component tests under realistic pressurized operating conditions of a pipeline.