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Based on basic equations of steady-state creep of spherically symmetric problems, a simple and efficient iterative method is proposed in this paper to determine creep deformations and stresses in thick-walled spherical vessels with varying creep properties subjected to internal pressure. The convergence of the proposed iterative method and the influences of varying and constant material properties on stresses and equivalent strain rate are discussed. How different material parameters involved in Norton's law affect radial and circumferential stresses together with the equivalent strain rate in thick-walled spherical vessels under internal pressure is investigated. [ABSTRACT FROM AUTHOR]

The concept of leak-before-break (LBB) is often used in safety cases for pressure systems, particularly, in the nuclear industry. An important factor in making a LBB case is in the prediction of the leak rate of fluid through a crack. This paper presents a summary of a program of work, which had the aim of improving guidance on leak rate evaluation for the LBB procedures in the R6 defect assessment methodology. Methods of calculating leak rates have been reviewed, and this has led to a crack morphology model being proposed, which represents single-phase isothermal compressible flow through a crack. In the crack morphology model, the flow is assumed by default to be fully rough turbulent, and the effective roughness to vary between a local roughness value for narrow cracks and a global value (i.e., the overall crack contours)for wide cracks. The effect of pressure drops due to changes in the flow direction at crack turns has also been included. Calculations using the model show that the friction factor relation due to Spence et al. (1991, "Leakage Flow Through Small Cracks--Report of Second Stage of Experimental Work," unpublished) gives .better agreement with measured flow rates than that due to Button et al. (1978, "Gas Flow Through Cracks," ASME J. Fluids Eng., 100, pp. 453-458), which tends to overestimate the flow rate for the examples studied. The inclusion of an inertial pressure term arising from changes in overall flow direction appears to be justified. [ABSTRACT FROM AUTHOR]

Assessment of the local thin area should be undertaken for both tension and compression bending. In this paper, simplified reference stresses for a flaw in a cylinder are proposed. By using these results, a newly developed p-M (internal pressure ratio and external bending moment ratio) diagram which can evaluate the collapse condition for pressure equipment such as vessels, piping, and storage tanks with a local thin area simultaneously subjected to internal pressure p and external bending moment M due to earthquake, etc., is proposed. The p-M line is verified by comparison with the finite element analysis results and the numerous results of experiment for a cylinder with a volumetric flaw obtained through the reference literatures. It was clarified that the differences in collapse limit between the p-M line and DNV guideline under both internal pressure and compression moment became evident where the outer diameter/wall thickness of a cylinder is large and the yield ratio of the material is small. [ABSTRACT FROM AUTHOR]