Analysis of Small Bore-Piping Vibration Phenomenon

This paper aims to develop a procedure for analyzing and assessing the vibration modes of small-bore piping connections. Then, the potential threat of fatigue failure can be detected earlier, and the stress monitoring, service life assessment, as well as the subsequent improvement task, can proceed smoothly. This study discusses the possible causes of the abnormalities of small-bore piping connections, the ranks of risk, and the methods of vibration measurement. We take the pipeline of a petroleum refinery as an example to illustrate the analysis procedure and then apply the finite element method to analyze the vibration modes of the abnormal small-bore piping connections investigated. From the simulation results, it is found that the guideline for the vibration-induced fatigue failure in process pipework proposed by the UK Energy Institute and EFRC (European Forum for Reciprocating Compressors) is too strict and needs to be amended appropriately. We use the finite element method to analyze the static stress distribution under the action of gravitation and the result is reasonable. In addition, the natural frequencies obtained from the vibration mode analysis of the pipelines investigated are very close to the field measurement values. The reliability of the numerical model and the analysis method is therefore confirmed. From the stress profile of the simulation results, the highest stress concentration occurs at the inner side of the bend, which is the potential location of the highest risk of fatigue failure and should therefore be monitored for the evaluation of fatigue life. From the result of harmonic response analysis, fatigue failure does not occur for the abnormal pipelines investigated. Finally, we use a reverse deduction method to find the vibration frequency and velocity corresponding to the fatigue limit stress of the pipeline. The guideline for the vibration-induced fatigue failure in process pipework proposed by the UK Energy Institute and EFRC is amended accordingly. The revised guidelines are expected to be helpful for the maintenance and repair personnel to diagnose the potential threats of fatigue failure and to proceed with subsequent prevention and improvement tasks.