High pressure stages of rotating machinery often produce high-frequency vibrations that cause failures in machinery components, pipes and their connections. Such failures happen even when the machinery operates well within design parameters. Predominant pressure patterns generated by rotating machinery are higher-order three-dimensional acoustic oscillations. In most cases, the piping/component failures result from high cycle events. In these events, a pipe shell is forced into unsteady sine wave deflections, producing deformation forces that initiate cracks, directly or indirectly, in the stress concentration areas. These are most dangerous in pipe welds, particularly in small bore attachment welds. For this reason, rapid detection and estimation of high cycle stresses associated with vibrations is highly desirable. For many years, researchers have studied and developed relationships for estimating maximum stress levels and predicting the service life of piping and machinery components. These studies have been carried out mainly in laboratory set-ups with components of limited size and, limited excitation strengths. In addition, the components were tested in a classical manner, i.e. their vibratory responses were related to their natural frequencies and non-resonant excitations were rarely considered. This work attempts to offer a simplified approach to correlate measured dynamic strain-stress with pipe wall vibrations for large diameter piping (NPS 36, wt = 19.7 mm) excited by a 27 MW centrifugal compressor. Diffused bending wave field and multimode excitation of the pipe shell constricted by factual boundary conditions are used. Particular attention is paid to the value distribution of the ratio (stress/strain to pipe wall velocity) in the straight pipe and in the areas of threadolet connections.

This content is only available via PDF.
You do not currently have access to this content.