Cylinder-cylinder Intersection Research Articles

Stress concentration factor based design curves for cylinder-cylinder connections in pressure vessels

The results of the parametric analysis of the cylinder-cylinder intersections in pressure vessels, performed in both elastic and plastic regions, are discussed in this study. Besides, the outcomes that contribute to the development of classical solutions in the literature are addressed as design curves depending on stress concentration factors (SCF). To begin with, the maximum stresses for cylinder-cylinder connections were calculated by finite element analysis and SCF values were obtained. In these calculations, external local loads acting on the nozzle centre and internal pressure are the main variables for loading conditions. Following that, different parametric approaches and loading conditions are presented to develop design curves for cylinder/cylinder connections by changing the main geometric parameters, such as cylinder and nozzle radii, and their thicknesses. A new approach is presented using these new curves thus allowing industrial designers to calculate maximum nozzle stresses without the need to undertake a thorough finite element analysis.

Dynamic Burst Pressure Simulation of Cylinder-Cylinder Intersections

In this study, the determination of the burst pressure of a series of cylinder-cylinder intersections representing vessels of diameter D and wall thickness T, and nozzles of diameter d and wall thickness t subjected to short-term dynamic loading is investigated. Dynamic simulations via the use of the finite element method are carried out to determine the effects of dimensionless parameters d/D, D/T, and t/T, as well as pressure versus time history. The LS-DYNA (1998, LS-DYNA Theoretical Manual, Livermore Software Technology Corporation) software is employed to model and analyze various intersections for the geometric parameter ranges 0.1≤d/D<1.0, 0.1≤t/T≤3, and 50≤D/T≤250. The use of both solid and shell elements is investigated and applied in this study. A correlation equation to predict the dynamic burst pressure of cylinder-cylinder intersections is proposed based on the parametric finite element analyses. Static test data are used to verify the dynamic correlation equation by applying a relatively long pressure pulse duration.

Material strain hardening in pressure vessel design by analysis

The effect of including material strain hardening on the gross plastic deformation (GPD) load of four sample problems from the EPERC Design by Analysis manual is investigated. The models considered are two axisymmetric vessels with flat heads under pressure, a nozzle/knuckle intersection under pressure, and a cylinder-cylinder intersection under combined pressure and moment loading. The results of limit analysis, large deformation elastic-perfectly plastic analysis, and small and large deformation bilinear hardening analysis are presented. Plastic loads are calculated using the ASME twice elastic slope (TES) criterion and the plastic work curvature (PWC) criterion. It is found that the plastic pressures given by the ASME TES criterion are inconsistent with respect to the limit load. The PWC criterion is found to represent strain hardening more consistently and lead to enhanced plastic loads. Von Mises equivalent plastic strain plots show that the form and extent of plastic deformation at the limit load in a perfectly plastic analysis and at the plastic load in a strain hardening analysis are similar, indicating a common definition of GPD.

Influence of Pad Reinforcement on the Limit and Burst Pressures of a Cylinder-Cylinder Intersection

The purpose of the paper is to provide experimental results for the limit pressure of a vessel-nozzle intersection under internal pressure with and without an intermediate pad-reinforced opening d/D=0.526. Two different methods, double elastic-slope and tangent intersection, are employed to determine the experimental limit pressure. A comparison of the limit and burst pressures with and without pad reinforcement is carried out. The present test results indicate that the pad reinforcement significantly improves the limit and the bust pressures. It can thus be concluded that pad reinforcement is an effective reinforcement method.

Einsatzgrenzen von T-Stücken mit Abzweigen gleichen Durchmessers

Auf T-Stücke mit Abzweigen gleichen Durchmessers in geschweißter oder ausgehalster Ausführung wird im Rohrleitungs- und Apparatebau aus verschiedenen Gründen zurückgegriffen. Das Berechnungsinstrumentarium für die festigkeitsmäßige Auslegung liegt nur für Innendruckbelastung vor. Zusätzliche Belastungen (Kräfte, Momente) sind quasi ausgeschlossen. Dieser Zustand kann nur durch die Anwendung numerischer Methoden aufgehellt werden. Dieser Untersuchung haftet die Besonderheit an, dass das Modell nicht als Grenzfall der normalen Zylinder-Zylinder-Durchdringung gewonnen werden kann. Es müssen spezielle Modelle für die geschweißte oder ausgehalste Ausführung erstellt werden, die dann parametrisiert für verschiedene Nenngrößen genutzt werden können. Das Konstruktionselement T-Stück ist beanspruchungsmäßig ein äußerst vielfältiges Bauteil, so dass es in der folgenden Untersuchung nach methodischen Gesichtspunkten hinsichtlich Tragfähigkeit und Ermüdungsfestigkeit analysiert wird. Die Ergebnisse machen deutlich, dass das T-Stück festigkeitsmäßig ein beachtliches Potenzial aufweist, das es allerdings nachzuweisen gilt. Limitations of Tees with Branches of Equal Diameter Welded and necked-out tees are frequently used in pressure vessel and piping design. Standard calculations based on the Kellog method are merely applicable for pressure loading. Supplementary forces and moments are excluded in this case. The application of numerical methods of structural analysis is extremely helpful in this situation. However, detailed modelling of the geometry is quite complicated and standard models of the cylinder-cylinder intersection type cannot be used. Special models of the welded and necked-out design variants have to be generated and parametrized in order to be applicable for different nominal sizes. Tees as structural components have to be considered under various aspects with respect to their mechanical behaviour. The following investigation proposes methods for design under static and cyclic loading conditions based on detailed FE analyses. The results reveal a considerable potential of tees which has to be proved by analysis.

A Finite Element for the Analysis of Shell Intersections

A specialized shell-intersection finite element, which is compatible with adjoining shell elements, has been developed and has the capability of physically representing the complex three-dimensional geometry and stress state at shell intersections (Koves, 1993). The element geometry is a contoured shape that matches a wide variety of practical nozzle configurations used in ASME Code pressure vessel construction, and allows computational rigor. A closed-form theory of elasticity solution was used to compute the stress state and strain energy in the element. The concept of an energy-equivalent nodal displacement and force vector set was then developed to allow complete compatibility with adjoining shell elements and retain the analytical rigor within the element. This methodology provides a powerful and robust computation scheme that maintains the computational efficiency of shell element solutions. The shell-intersection element was then applied to the cylinder-sphere and cylinder-cylinder intersection problems.

A method of design by analysis to evaluate cylinder-cylinder intersection under internal pressure

This paper proposes a method of design by analysis to evaluate the stress intensities under internal pressure in the neighbourhood of a cylinder-cylinder intersection, especially for d D > 0·5 . Based on three-dimensional finite element results, the main procedure of this method is as follows: 1. (1) location and determination of lines for the treatment of stresses; 2. (2) initiation of the stress distribution curve and decomposition of stresses; 3. (3) evaluation of stress intensities of different stress categories. This paper gives a graphical presentation of the calculation procedure and also gives an engineering application of this method in which a satisfactory result was obtained.

A Finite Element Model to Analyze Cylinder-Cylinder Intersections

A finite element model is proposed to study the stresses in the neighborhood of a cylinder-cylinder intersection. In particular, diameter ratios greater than 0.5 are focused upon since little information is available in the ASME Boiler and Pressure Vessel Code or in the literature about the stress concentration for these geometries. The aim of the present work is to validate such a model for internal pressure loading. To accomplish this, various parametric finite element studies were conducted. The selected model is then validated by applying it to various available cylinder intersection models and comparing the results. The finite element results are further compared with a solution obtained using a shell theory.

Approximate methods of inelastic design

A simple approach to the analysis of components operating below the shakedown limit and within the creep range is described. An example of the application of the approach to the creep rupture of a cylinder-cylinder intersection is given and potential difficulties are discussed. The paper then addresses the problem of structural response beyond the shakedown limit and seeks to define those structures and loadings which will give acceptable ratchetting rates.

Some Further Comments on Limit Pressures for the Cylinder-Cylinder Intersection

Some Further Comments on Limit Pressures for the Cylinder-Cylinder Intersection

Review of Lower-Bound Limit Analysis for Pressure Vessel Intersections

On the basis of a study of several recent papers concerned with the lower-bound computation of the collapse load of pressure vessel intersections, a review is made of the satisfaction, or nonsatisfaction, of the requirements of the lower-bound theorem of limit analysis. It is shown that, whereas for rotationally symmetric structures true lower bounds have been obtained, for a nonsymmetric case such as a right cylinder-cylinder intersection it is difficult to avoid so me approximations. If attempts are to be made to develop general purpose limit analysis programs, the consequences of approximations of the type used so far must be evaluated with care if significant results are to be obtained.

On limit analysis of cylinder-cylinder intersections subjected to internal pressure

The problem of lower bound computations for tee connections under internal pressure and other loadings is examined. It is shown that the requirements of the lower bound theorem of limit analysis have not been satisfied in some recent publications. A new approach is briefly described and the difficulties inherent in the proper determination of a lower bound are discussed.

EURCYL — a computer program to generate finite element meshes for cylinder-cylinder intersections: de Windt, P. and Reynen, J. Joint Nuclear Res. Centre, Ispra Est., Italy (August 1973) 22 pp

EURCYL — a computer program to generate finite element meshes for cylinder-cylinder intersections: de Windt, P. and Reynen, J. Joint Nuclear Res. Centre, Ispra Est., Italy (August 1973) 22 pp

The calculation of thermal stresses in a cylinder-cylinder intersection by means of finite elements

The calculation of thermal stresses in a cylinder-cylinder intersection by means of finite elements

A Simple Technique for Calculating Shakedown Loads in Pressure Vessels

A fundamental examination has been made of the post-yield behaviour at discontinuities in pressure vessels with a view to determining shakedown loads. The results of this indicate that a simple graphical construction can be devised whereby such loads are easily determined with only a knowledge of the elastic stresses and a yield criterion; in particular, a ‘five line construction’ method is suggested which can be applied to a wide range of engineering stress problems. The method is exemplified by a study of shakedown loads for both flush cylinder-sphere and cylinder-cylinder intersections under internal pressure, and the implications of the results in terms of current design philosophies are discussed.