Forecasting Dynamic Loads in Gas Pipelines Based on Identification Methods

Abstract

Internal gas pressure is one of the main force influences that determine the stressed state of pipelines. The thickness of the walls of the pipes of the main pipelines is usually determined only on the basis of the internal pressure of the product. However, the constructive solution of the pipeline as a building structure is chosen taking into account all possible impacts for the adopted pipeline layout. Under the influence of internal pressure, annular tensile stresses arise in the tubes, which are calculated from the membrane theory of thin-walled cylindrical shells, neglecting the change in the radial stresses along the tube thickness and the initial imperfection of the cross-sectional shape. Although owing to the non-roundness of the tubes (the deviation of the cross-sectional shape from the circular one), along with the ring tensile stresses, flexural stresses also arise, but they are not taken into account in the calculations for the limiting states. This is due to the fact that within the limits of pre-starts, set for the non-roundness (the ratio of the actual diameter of the pipe to the nominal one), the destructive pressure is practically the same for pipes with different non-roundness. However, there are cases when the limiting state for a pipeline is not its destruction, but a certain level of allowed voltages. This applies to pipelines that transport gas with hydrogen sulphide content. Studies have shown that the tendency of such a pipeline to corrosion destruction becomes higher with the greater concentration and partial pressure of hydrogen sulphide and the strained state of the pipeline. To ensure reliable operation of such systems, the permissible maximum voltage is determined depending on the yield strength of the pipe metal. When determining the ring stresses from internal pressure, it is necessary to take into account the initial non-roundness of the pipeline section. The authors show the possibility of evaluating the alternating stress component in a pipe wall by fluid pressure pulse measurements. The mathematical model of the problem solved and experimental results are presented.