High-pressure gas pipelines are usually designed for a specific internal pressure as the governing load parameter. Apart from the internal pressure, however, pipelines may also be subject to other significant loads. These additional loads often lead to longitudinal stresses in the pipeline. So far, the relevant German technical codes and standards do not provide a concept for assessing longitudinal and/or bending stresses.
International standards and publications dealing with additional longitudinal or bending stresses often refer to failure criteria that are either based on the concept of critical strain or critical stress, but neither of these concepts has been transposed directly into the German codes and standards.
Open Grid Europe GmbH - the largest TSO in Germany - recently started using an IMU (Inertial Measurement Unit) as part of its pipeline pigging operations, which allows detecting bending strain in the pipeline. This makes it possible to also consider longitudinal stresses in addition to the internal pipeline pressure when it comes to assessing the integrity of a pipeline.
One question that remains concerns the limiting criterion to be applied in the case of multi-axial loads. The aim of this project therefore was to propose a sufficiently conservative approach to assessing bending strain.