A Frequency-Domain Screening Methodology for Flow-Induced Vibration in Piping

A three-tiered approach is advocated to assess the level of flow-induced vibration (FIV) threat to process piping due to internal flow. The first-tier assessment is a high-level design check on the possibility of FIV. The tier-1 screening does not provide a framework for the direct estimation of vibration levels, stress, or fatigue damage. The third-tier assessment is termed a comprehensive screening and relies on computational fluid dynamics (CFD) to predict the flow-induced forcing, coupled to a structural finite element model to obtain the response of the piping (vibration levels and stresses), from which an estimate of fatigue damage at critical locations is computed. The tier-3 screening may be computationally intense (e.g., for multiphase flow) and is generally not fast to perform. This paper presents a second-tier assessment (intermediate between the tier-1 and tier-3 screenings), where the flow-induced loading is represented by power spectral density (PSD) curves, which are inputs to a structural finite element model of the piping. The structural finite element analysis (FEA) is performed in the frequency domain, implying fast turnaround time requiring short computing time. The FEA yields a prediction of vibration levels and dynamic stress, from which the sought-after estimates of fatigue damage are computed. The outcome of a tier-2 screening for vibrating piping in a metering skid is presented and the predictions compared against field measurements using accelerometer data (vibration levels) and strain gauge data (dynamic stress). A tier-2 screening is performed for a subsea water injection jumper and the results compared against those of a tier-3 screening.