ESDU 87019 draws on the available data in the literature to predict the critical velocity through the bundle for the onset of fluidelastic instability for all likely tube arrangements. The results depend on both tube natural frequency and damping; a method of calculating natural frequency is included and data for predicting damping for gases or liquids are provided. Other mechanisms causing tube vibration@ such as buffeting and wake shedding@ are considered but are less likely to cause damage. Methods of reducing the risk of the vibration at the design stage are discussed. A comprehensive worked example@ showing the detail of the calculation from a knowledge of a practical exchanger geometry@ illustrates the use of the method@ and the accuracy of the prediction is assessed.