A novel investigation into the application of non-destructive evaluation for vibration assessment and analysis of in-service pipes

Flow induced vibrations that are close to resonance frequencies are a major problem in all oil and gas processing industries, so all piping systems require regular condition monitoring and inspection to assess changes in their dynamic characteristics and structural integrity in order to prevent catastrophic failures. One of the main causes of pipe failure is weak support causing low frequency high amplitude flow-induced vibration. This causes wear and tear, especially near joints due to their dissimilar stiffness resulting in fatigue failure of joints caused by vibration-induced high cyclic stress. Other contributing factors in pipe failure are poor or inadequate design, poor workmanship during installation or maintenance and inadequate or weak and flexible support. These pipes are usually required to work non-stop for 24 hours a day 7 days a week for weeks, months or years at a time. Regular monitoring and in-service dynamic analysis should ensure continuous and safe operation. A novel method of non-destructive testing and evaluation of these pipes, while in service, is proposed in this paper. This technique will enable early detection and identification of the root causes of any impending failure due to excess vibration as a result of cyclic force induced by the flow. The method pinpoints the location of the impending failure prior to condition-based maintenance procedures. The technique relies on the combined application of Operating Deflection Shapes (ODS) analysis and computational mechanics utilizing Finite Element Analysis (FEA), i.e. linear elastic stress analysis. Any structural modification to the pipes and their supports can then be applied virtually and their effects on the system can be analysed. The effect on vibration levels is assessed and verified. The effect of any change in the forces corresponding to changes in the Differential Pressure (DP) at constant flow rate through the pipes can then be estimated. It was concluded that maintaining the differential pressure above some “critical” threshold ensures the pipe operates under the allowable dynamic stress for a theoretically “indefinite” life cycle

Doorway States in the Gamma Decay-out of the Yrast Superdeformed Band in 59Cu

The decay-out process of the yrast superdeformed band in Cu-59 has been investigated. The firm determination of spin, parity, excitation energy, and configuration of the states involved in this process constitutes a unique situation for a detailed understanding of the decay-out mechanism. A theoretical model is introduced that includes a residual interaction and tunneling matrix element between bands, calculated in the configuration-dependent cranked Nilsson-Strutinsky model. This interaction causes the decay to occur via a small number of observed doorway states

Conservation of the K-quantum number in warm nuclei

The selection rules on the K-quantum number in rapidly rotating warm nuclei are investigated analyzing quasi-continuum spectra feeding into low-K and high-K bands in Er-163. The data are compared to simulated spectra obtained using the band mixing model predictions including the residual interaction and a term representing the effect of the Kquanturn number on the rotational energy. K-selection rules are found to be obeyed by the decay along excited unresolved rotational bands of heat energy up to around 1.2 MeV and angular momentum 30h <= I <= 40h. In contrast, the results corresponding to higher heat energy of 1.2 to 2.5 MeV indicate that the selection rules are only partially satisfied

Conservation of the K-quantum number in warm nuclei

he selection rules on the K-quantum number in rapidly rotating warm nuclei are investigated analyzing quasi-continuum spectra feeding into low-K and high-K bands in 163Er. The data are compared to simulated spectra obtained using the band mixing model predictions including the residual interaction and a term representing the effect of the K-quantum number on the rotational energy. K-selection rules are found to be obeyed by the decay along excited unresolved rotational bands of heat energy up to around 1.2 MeV and angular momentum 30Planck's over 2piless-than-or-equals, slantIless-than-or-equals, slant40Planck's over 2pi. In contrast, the results corresponding to higher heat energy of 1.2 to 2.5 MeV indicate that the selection rules are only partially satisfied

Compound and rotational damping in warm deformed rare-earth nuclei

The \u3b3 decay in the quasicontinuum from selected configurations of the rotational nucleus 163Er has been measured with the EUROBALL array. A new analysis technique has allowed for the first time to directly measure the compound and rotational damping widths \u393\u3bc and \u393rot. Values of \u393\u3bc 4820\u2009\u2009keV and \u393rot 48200\u2009\u2009keV are obtained in the spin region I 4830\u201340\u210f\ufe00, in good agreement with microscopic cranked shell model calculations. A dependence of \u393\u3bc and \u393rot on the K-quantum number of the nuclear states is also presented

Warm rotating nuclei: damping mechanisms and the order-to-chaos transition

The $\gamma$ decay in the quasi-continuum is used as a probe of nuclear structure properties in thermally excited nuclei. The experimental analysis is performed on high-statistics EUROBALL data on $^{163}$Er, and the results are compared to band mixing calculations for this nucleus. Two topics are investigated. First, a direct experimental measurement of the rotational and compound damping width ($\Gamma_{rot}$ and $\Gamma_{\Mu}$) is given. From a line-shape analysis of $\Gamma-\Gamma$ coincidence spectra values of 200 and 20 keV are obtained for $\Gamma_{rot}$ and $\Gamma_{\Mu}$, respectively, in the spin region I $\approx$ 30–40$\hbar$, in good agreement with theory. Secondly, the validity of the selection rules associated with the $K$-quantum number are investigated as a function of the internal energy $U$ above yrast. $K$-selection rules are found to be obeyed in the decay along discrete unresolved rotational bands up to U$\approx$1.2 MeV, while in the interval U$\approx$1.2–2.5 MeV, where the order-to-chaos transition is expected to take place, selection rules are found to be only partially valid

Damping mechanisms and order-to-chaos transition in the warm rotating Er-163 nucleus

The gamma decay in the quasicontinuum is used to study the order-to-chaos transition in the thermally excited Er-163 nucleus. The experimental analysis is performed on high-statistics EUROBALL data, focusing on the spin region I approximate to(20-40)h, and internal excitation energy up of approximate to 2.5 MeV. The results are compared to cranked shell model calculations for this nucleus, taking into account the dependence on the K quantum number. Two main topics are investigated. First, the validity of the selection rules associated with the K quantum number are studied as a function of the internal energy U above yrast. K-selection rules are found to be obeyed in the decay along discrete unresolved rotational bands up to U approximate to 1.2 MeV, whereas in the interval U approximate to 1.2-2.5 MeV, where the order-to-chaos transition is expected to take place, selection rules are found to be only partially valid. Second, the line-shape analysis of gamma-gamma coincidence spectra provides a direct experimental measurement of the rotational and compound damping widths (Gamma(rot) and Gamma(mu)), yielding values of 200 and 20 keV, respectively, in good agreement with theory