Integrity of pressurized components with localized corrosion under internal pressure and transient thermal loading

This paper is devoted to the modelling and analysis of the problem of the safety and residual lifetime of pressurized components (e.g. pressure vessels, apparatus, pipelines) with zones of local corrosion damage. Corrosion damage is the most common form of structural material degradation in service conditions, in particular, in the chemical and gas, and oil industries. Attention is paid to nonstationary regimes of the component operation, e.g., start‐stop regimes. It is shown that the critical parameters calculated taking into account the nonstationary loading can be lower compared with ones determined for the stationary regimes, e.g., on the basis of the ASME Code B31G.     

Linear and nonlinear parametric instability behavior of cylindrical sandwich panels subjected to various mechanical edge loadings

Linear and nonlinear dynamic instability behavior of cylindrical sandwich panels subjected to combined static and dynamic nonuniform in-plane loadings is studied in this article. The core compressibility effects are considered in the model by assuming fourth and fifth order expansions for the transverse and tangential displacement of the core. The exact stress distributions within the panel are determined by panel prebuckling analysis for the applied parabolic and partial edge loadings. Galerkin's method is used to reduce the governing partial differential equations of the shell panel into a set of nonlinear ordinary differential equations. Dropping the nonlinear term, dynamic instability regions are obtained by solving the Mathieu-type differential equation by the method of Fourier series. The characteristics feature of the stable and unstable regions are investigated by linear and nonlinear time history responses and phase plots of the shell panel in those regions using Newmark's time integration. Incremental harmonic balance (IHB) method is used to study the nonlinear frequency amplitude responses of the cylindrical sandwich panels.     

Techniques for the investigation of the ratchetting behaviour of piping components under internal pressure and simulated seismic loading

The ratchetting behaviour of piping components under internal pressure and simulated seismic loading has been investigated using special fixtures and a standard laboratory universal testing machine fitted with a fatigue module. Experimental arrangements are presented for testing plain pipes with or without thinned sections, elbows and tee branch junctions under in-plane dynamic bending; similar fixtures and arrangements could be used for reducers and flanged connections and other types of loadings. Input accelerations up to 5g have been achieved and the results demonstrate that a great deal can be learnt about piping component behaviour from such simple arrangements and without resorting to sophisticated or expensive experimental techniques. The necessary instrumentation and algorithms for the analysis of results are described. Some sample results are included and discussed in terms of overall piping component behaviour. Two recommendations are suggested to more realistically simulate typical earthquake input spectra.     

Formulation and characterization of alprazolam-loaded nanoliposomes: screening of process variables and optimizing characteristics using RSM

This research study aimed to develop a novel sustained release formulation of alprazolam that can also be used for transdermal delivery. This was carried out, for the first time, through encapsulation of alprazolam in nanoliposomes using ethanol injection. In order to obtain the best formulation, four process variables, including the solvent/nonsolvent volume ratio, phospholipid concentration, alprazolam concentration, and cholesterol content were considered as key factors. Response surface methodology (RSM) and a central composite design (CCD) model were used to investigate the effect of these factors on vesicle size (VS) and encapsulation efficiency (EE) as the major properties of nanoliposomes. Experimental data were statistically analyzed, and two significant quadratic models were developed to test the VS and EE responses. The findings indicate that alprazolam and phospholipid concentrations have a significant effect on the mean VS. However, EE was significantly affected by both the alprazolam and phospholipid concentrations and the cholesterol content. The optimized formulation for preparation of alprazolam-loaded nanoliposomes with appropriate VS and EE was suggested. Small unilamellar vesicles (SUVs), ranging in size from 50 to 100?nm were clearly observed in the transmission electron microscopy (TEM) images, which is appropriate for transdermal delivery of alprazolam. The study of the prepared nanoliposomes over 28 days at 4?°C confirmed the stability of the formulations containing cholesterol. The results of an in vitro release study of alprazolam-loaded nanoliposomes in phosphate buffered saline (PBS), pH 7.4 for 24?h at 37?°C using dialysis, indicated the sustained release of alprazolam due to encapsulation.