Papers by Keyword: Critical Pressure

Abstract: In the straight-seam tubes, the appearance of defects in the area of the welding seam welded under the flux layer and the seam geometry are closely related to the technology and metallurgy of welding process. Possible defects are the pores, incisions, slag inclusions and cracks. The pores can appear in different shapes, with different distribution and in different amounts during the solidification of welding seam. When molten metal solidifies, the gas bubbles can come to the surface or remain inside the metal. The incisions may occur due to the fact that the juncture is not completely filled. Such incisions, passing most often along the edge of welding seam, are explained by the discrepancy between the amount of metal deposited per unit of time and the volume of the juncture. The occurrence of the slag inclusions is determined by the metallurgical reactions between the slag and the drop, separating from the end of the electrode, as well as the bath of molten metal. The cracks differ depending on the size, the nature of location and the causes. There are the macro-cracks and micro-cracks, the hot and cold cracks. In this paper the critical in-tube pressure, at which the destruction of tube occurs at the partial faulty fusion of the tube’s welding seam, is obtained. The results can be used in the diagnosis of the causes of the destruction of the steel large-diameter tubes of the main gas-oil tube-lines.

Abstract: The stability of submerged functionally graded (FG) cylindrical shell under hydrostatic pressure is examined in this paper. Based on the Flügges shell theory, the coupled frequency of submerged FG cylindrical shell is obtained, using wave propagation method and Newton method. Then the critical pressure of FG cylindrical shells is given by applying linear fitting method. Results are compared to known solutions, where these solutions exist. The effects of constituent materials, volume fraction, boundary condition and dimensions on the critical pressures of submerged FG cylindrical shell are illustrated by examples.

Abstract: Stability is the key of designing thin-walled external-pressure Vessels. Nonlinear buckling analysis using finite element method has been carried out on a processor unit of an autonomous underwater vehicle to study the stability of the processor unit considering the screw tightening. Effects of the cylinder thickness on the critical pressure are discussed. Results show that the buckling wave number is 4 in the circumferential direction, and the critical pressure decreases with decreasing the cylinder thickness exponentially, which is in good agreement with the theoretical calculation.

Abstract: Serious problems arise when the magnetic fluid seal technology is needed to use in assemblies working in water or other liquid environment. Some efforts have been up to time made to design hybrid, two stage sealing structures with shields or mechanical seals used as protection measures to the magnetic fluid seal. Anyway, earlier or later there is always problem with direct contact between magnetic fluid and the environmental liquid. In the paper are presented results of experiments carried out with one stage rotating magnetic fluid seal operating in an direct contact with utility water. The special test procedures have been elaborated and practically used, with the aim to define main characteristics of magnetic fluid seals and to simplify experiments. These characteristics were: critical pressure, critical motion velocity and working life of the seal. Four grades of commercial, silicon based magnetic fluids of hydrophobic properties were tested in a single stage sealing system. The results of tests are presented in the form of tables and diagrams. It is concluded that hydrophobic commercial magnetic fluids could be efficiently used in rotating shaft seals however within limited and rather low range of motion velocity.

Abstract: Densely arranged underground steel tube system (DAUSTS) is a new kind of structure which can be usually used in constructing spacious underground structures such as metro stations. During the construction, the steel tube is horizontally forced into soil by jacks through a vertical well. The tube may generate local buckling phenomena under the compression force if the parameter of the tube and soil meet the buckling condition. In the paper, the soil perturbation mode and the deformation of the tube before local buckling are both analyzed, considering the possibly concerned buckling failure modes in practical engineering, the confine effect of the soil and interaction between the tubes. A nonlinear buckling analysis on tube-wall of the steel tube located in the most unfavorable place is developed by the arc-length method of the finite element method (FEM), considering the effect of the large deformation. The results of the numerical simulation matches very well to the real application and the key results of the analysis can be used as an estimation principle for the stability of the tube.

Abstract: The elastoplastic instability of the symmetrical double-arc ring-stiffened cylindrical shell was analyzed. The critical pressure was obtained for small deflection elastoplastic buckling of the cylindrical shell under hydrostatic pressure. The critical pressure for large deflection buckling of the cylindrical shell with initial geometric imperfections was determined under hydrostatic pressure by using nonlinear large deformation theory. The effects of hoop equivalent wave number, initial geometric imperfection and the central angle of circular arc on buckling mode and critical pressure of double-arc ring-stiffened cylindrical shell were analyzed. The results showed that the hoop equivalent wave number of arc cylindrical shell had an main effect on the critical pressure of the structure, designed equivalent hoop wave number of double-arc cylindrical shell should not be approach to the hoop wave number corresponding to minimum critical pressure, and the central angle of circular arc had less effect on critical pressure of the structure.