Advanced Methods for Vibration Reduction at a Piping

Safe operation, availability and lifetime assessment of piping are of utmost concern for plant operators. This paper presents the first results of the European research project IRIS (Integrated European Industrial Risk Reduction System) [1]. One important IRIS goal is to identify risk reduction methods to avoid high cycle fatigue at a large vertical pipe system. The piping system is supported by a tall structure fixed at the base. As a result, the steel building stiffness decreases with height. Furthermore large piping-elbow forces act at the top of the building, which lead to large vibration amplitudes. Since both piping system and supporting structure exhibited these large vibration amplitudes, dampers or shock absorbers placed between them would prove ineffective. Therefore, special vibration absorbers were developed for such piping systems. The paper presents the design process, starting with an extensive system investigation up to the passive multi-axial vibration absorber design parameters. The aim was to establish a good basis for the risk reduction of vibration induced emergency conditions by use of vibration absorbers. This included: • Laboratory tests with a mock-up pipe system, where the first design ideas for new passive vibration absorbers were investigated. • Vibration measurements were carried-out to investigate the current state of the vibration behavior. • The piping system was inspected; strain gauges were used to identify stress concentrations at welds and other notches due to ovalization. • Finite element calculations were performed, first as a combined beam and shell model for the pipe without the support structure. • A detailed model for the combined steel construction and pipe system was created. • Modal-updating was done to fit the calculated model to the experimental modal analysis data. • Load simulations were created to describe the mass flow excitation. • Harmonic frequency analysis was performed. • On the basis of these calculations design parameters for the passive vibration absorber were determined. Finally, a solution for the design of the two passive vibration absorbers will be presented.