Acoustically or Flow Induced Vibration (AIV/FIV)
ACOUSTICALLY INDUCED AND FLOW INDUCED VIBRATION: LITTLE-KNOWN FAILURE MODES NOW ADDRESSED IN AS/NZS 2885.1:2018
Introduction to the issue:
During pipeline depressurisation and repressurisation operations, high gas velocities and mass flow rates induce vibration and cyclic stressing, which can result in station piping fatigue damage and failure.
The same can occur during station pressurisation events, if the process conditions are such that high vibration levels are experienced.
A recent major gas pipeline design investigation discovered two types of vibration concerns which would manifest during both pipeline depressurisation and repressurisation operations, and to a lesser extent during facility and pig trap pressurisation operations. Until now, these forms of vibration have not been widely understood nor considered by Designers within the Australian pipeline industry. The vibration types of concern are Acoustically Induced Vibration (AIV) and Flow Induced Vibration (FIV).
Achieving a safe rectification of the design without a full shutdown of the entire pipeline system required significant data collection, analysis, simulation modelling, and extensive re-design effort. This paper will describe what was essentially a major research project, with safety and system integrity as ultimate objectives.
The discovery of AIV and FIV issues on this operating pipeline, together with knowledge gained through the design and engineering process to mitigate these forms of vibration, resulted in recommended changes to AS 2885.1-2012. These changes, led by the authors, appear in the latest release of AS/NZS 2885.1:2018, and provide guidance to pipeline Designers to avoid AIV and FIV problems.
The paper, delivered at the 2019 APGA Conference in Adelaide, explains the causes and nature of both types of piping vibration and explains why certain changes were made to AS 2885.1-2012. The changes are discussed, with concluding advice as to how these changes should be applied by pipeline Designers, and what pipeline Owners and Operators should do for their operating assets.
Keywords (for Search function): Abnormal Operations, Blowdown, Depressurisation / Repressurisation, Severe Service, Throttling, Above-ground piping, MLV Assemblies, Pipeline Assemblies, Station Piping design, Acoustic vibration, Flow-induced vibration