Abstract

Vibration-induced problems on Heat Recovery Steam Generators (HRSGs) are observed at numerous plants. Here the focus is on vibration caused by the gas turbine exhaust gas, which can lead in some cases to significant damage and/or failures to the internal pressure parts (piping, tube modules), structures and casing. The different types of flow-induced vibration mechanisms, such as turbulent buffeting, vortex shedding, fluid-elastic instability etc. are described in some detail. Analytical techniques to evaluate the risk of their occurring and predicting their magnitude and how these can be applied to different HRSG designs are described. Strategies for assessing the impact of vibration in the field are presented, with guidance on conducting effective visual inspections and how to plan and perform in-service vibration measurements. A selection of real-life case studies from plants in the USA, Middle East and South-East Asia are used for illustration, comprising several types of vibration-induced failures, results of inspections and in-service measurements. The cases presented illustrate the importance of how the knowledge and experience of the boiler designer regarding vibration risks are key to avoiding significant economic losses to the owner/operator, given that the cost impact of repairs to the asset can be very significant. A set of recommendations is provided for improvements in HRSG designs based on these field cases.

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