Flange joint leakage is one of the common maintenance problems in refineries and chemical plants. This paper studies the effect of external loads on the strength and leakage behavior of flanged joints. Finite element and analytical methods are compared, and the proposed method is compared with leakage data. The common “equivalent pressure” method is shown to be very conservative, and a method of evaluating external loads is recommended.
The isochronous stress–strain method for creep evaluation in pressure vessels is a very effective and efficient alternative analysis method to the rigorous time dependent numerical approach. However, the isochronous data are generated from uni-axial load-controlled constant stress state. Its constraints or limitations have not been systematically studied for general or three-dimensional state of stress and variable loading conditions. In reality, pressure components are subjected to complex and combined loading conditions that may vary during operation, resulting in general state of stress and nonconstant loads. In this study, the accuracy of the isochronous stress–strain method for general state of stress and the concept and application of differential isochronous stress–strain data for slowly time-varying loads are brought up and investigated, wherever the time-varying loads can be approximated by piecewise constant step functions. By introducing the differential curve, the isochronous method is expanded into certain nonconstant loading conditions.
The design of components or structures at elevated temperature is complex. The use of rigorous time dependent material models may not be practical for many large scale industrial problems. The use of simplified methods permits the creep analysis of components that would be impractical by rigorous time dependent models. The Isochronous Stress-Strain method is an approach that has been used extensively for the creep evaluation of elevated temperature components. The method has been used for the analysis of problems containing both primary and secondary stresses. The method has also been used to evaluate creep buckling problems. Although the method has been accepted as an alternative to a full time dependent creep analysis, the limitations and accuracy of the method have not been investigated systematically and are not fully understood. This study compares the isochronous stress-strain method with a generalized time-explicit creep model for materials in high temperature applications. Analytical solutions are developed for three basic loading configurations, including uniaxial tension, pure bending, and torsion in either load or displacement controlled conditions. Deformations, stresses, and creep strains are compared between the two different methods.
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