Parametric Study on the Vibration of Small-Bore Piping Branch Connections

Abstract

In vibration service, small-bore piping connections, especially unsupported cantilever configurations, are associated with a high level of concern as potential fatigue crack initiation locations. Various international guidelines and procedures address the assessment of piping vibration in general and of small-bore connections in particular. In this work, a review of these guidelines as applied to a specific class of small-bore connection was performed by means of a finite element parametric study on a large number of branch connections. The small-bore configuration evaluated in this work is an unsupported cantilever connection made using an integrally reinforced forged branch fitting with butt-welded joints. At the end of the branch is a flanged connection with either a blind flange only, or a single or double valve with a blind flange. For the parametric study a random distribution of run pipe diameter and thickness and branch pipe diameter, thickness, and length was used to evaluate a few thousand different small-bore configurations. Modal analysis was used to determine the relationship between stress and velocity at two critical locations: the weld between the branch fitting and header and the weld between the branch pipe and branch fitting. Results of the parametric study were processed and compared to the evaluation criteria of a number of established and upcoming guidelines and standards.