Three-Level Safety Evaluation of Suspended Sections of Underwater Buried Pipelines

Abstract

The uneven riverbed, as well as the impact and erosion suspended on by water flow, make the underwater crossing pipeline vulnerable to exposure and suspension. Under the influence of water flow, the span of a suspended pipe section steadily grows, jeopardizing the integrity of pipeline operation. In order to investigate the mechanical properties and failure behavior of the suspended section of the crossing pipeline under the influence of water impact, according to the failure mechanism of the pipeline, the statics and dynamics analysis of the pipeline is carried out, and the graded safety evaluation technique of the crossing pipeline with suspended section is presented. First, a “static strength safety evaluation under static load condition” (level 1) is carried according to the mechanical features and stress state of the pipeline's suspended section. Second, the "resonance safety evaluation under dynamic load" (Level 2) is carried in accordance with the correlation between the natural vibration frequency of the suspended pipeline and the vortex emission frequency of water flow. Finally, the periodical change process of the pipeline's alternating stress is studied, the fatigue damage and fatigue life of the pipeline are solved, and the "fatigue strength safety evaluation under dynamic load condition" (level 3) is performed. Thus, a three-level safety assessment procedure for pipelines crossing the suspended section is suggested. The pipe stabilizing measures that fall short of the safety evaluation are suggested, and based on the calculation example, a specific calculation process is provided. This information serves as a theoretical guide for the safety evaluation of the suspended section of the underwater crossing pipeline.