Guidelines for the field-based vibration assessment of pressure vessel nozzles

Abstract

Vibration analysts rely on industry guidelines and international standards for the “screening” of piping vibration datasets, i.e., to differentiate locations of high piping vibration (usually high dynamic stress) from acceptable piping vibration. Despite the abundance of piping vibration criteria, analysts continue to develop advanced screening methods to discard “false positives” at the data collection stage, i.e., measurement locations with high vibration (exceeding vibration limits) but with acceptable dynamic stress. The present work is a contribution to the growing body of advanced screening methods and aims to identify the most suitable vibration limit curves for the field-based vibration assessment of pressure vessel nozzles. This sub-category of process pipework requires special attention due to the relative flexibility of the parent pressure vessel and the relatively stiff geometry of nozzles compared to general pipework. The harmonic response problem of a cylindrical nozzle radially intersecting a thin-walled cylindrical pressure vessel and vibrating at its fundamental bending modes is solved using a three-dimensional Finite Element (FE) model. The results of the parametric FE study suggest that frequency-dependent vibration velocity criteria, such as the Energy Institute (EI) guidelines, are more suitable for assessing vibration severity on pressure vessel nozzles than constant vibration velocity criteria, such as the ISO 20816-8.