Safety assessment method for exposed crossing pipelines caused by river scouring

Flood scouring the river bed where the directional drilling crossing pipeline is located may lead to pipeline exposure above the riverbed, as well as pipeline suspension and failure. The failure mechanism of pipeline during the whole process from initial exposure to fatigue failure under the action of hydrodynamic force was studied and the safety assessment method of the exposed pipeline due to scouring was proposed through the lateral stability, strength failure and suspended span fatigue analysis. In addition, safety assessment was performed for two actual pipelines with the solution was developed. The results indicate that the pipeline in Example 1 is in safe state for the maximum equivalent stress of the exposed pipeline is 176 MPa, which is less than the minimum yield strength of the pipeline, and there is no suspension. However, the pipeline in Example 2 cannot operate any more for the scouring time of flood on the pipeline exceeds its fatigue life during exposure. Thus, the research results provide theoretical support and basis for the safety assessment and the development of the replacement scheme of scoured pipelines.