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Finite Elements Analysis

In order to evaluate the static stress values into the body structure and the internal parts of the valve under design, upset and operating conditions, several calculations are performed at REMOSA, paying particular attention to:

• stress conditions in the valve body, especially in those parts affected by geometrical discontinuities - abrupt shape variations, connections between conical/cylindrical shells and plate shells and similar points;
• stress conditions in the body parts involved by dissimilar weldings, different thickness and differential thermal expansion coefficients;
• evaluation of strain and stress states in the internal parts under design and upset conditions;
• evaluation of the design clearance between the internal parts under the design and upset conditions.

The following ASME Codes are applied:

• ASME Section VIII Division 2 - Appendix 4 - Mandatory design based on stress analysis - for the interpretation of the obtained results;
• ASME Section VIII Division 2 - Appendix 5 - Mandatory design based on fatigue analysis - for the fatigue analysis in peak stress areas.

FEA analysis has been performed using two different software packages: FEMAP for pre-processing and post-processing operations and NE/Nastran as FEA Solver.

Produced by EDS-SDRC, FEMAP is a finite element modeling and post-processing system which is used for exporting the input file to the Solver and reading the results from the Solver, providing powerful tools for visualizing and reporting.

NE-Nastran is a Nastran (NASA Structural Analysis System) native Solver enhanced by Noran Engineering, Inc.

NE-Nastran applications include almost every type of structure and construction. Structural and modeling elements are provided for the specific representation of the more common types of structural building blocks including rods, beams, shear panels, plates, shells of revolution and solids.

A set of specific pre-processors and post-processors has been developed by REMOSA to obtain the combination of stress values required by ASME Codes.

The elements commonly used to build a valve model are "plate/shell" elements, in order to obtain the stress values and their combinations as required by ASME Codes.

The models represent the steel structure of the valve only, without any refractory lining component. This is in accordance with the rules that do not consider the refractory lining as capable of providing any resistance. The software used to perform the calculation can automatically evaluate the weight of the structure by its geometry and description.

The refractory lining weight is taken into account changing the mass density of the materials with calculated equivalent mass densities for each material employed in the model. These equivalent mass densities are able to restore the real weight of the valve for the geometrical model, to obtain a correct evaluation of stresses due to gravity.

The real position of the valve during its service is taken into account by decomposition of the gravity force along the local coordinate system of the valve.

The geometry of the model represents the middle surface of the valve body, bonnet and internal ducts. The geometrical dimensions are directly derived by construction drawings while the thickness of the parts is inserted during the pre-processing of the data in order to prepare the data file used by the numerical processor.

For the stress analysis of internal parts, elements type "brick" are used as a rule, because of the ratio between the main dimensions of these elements. Using these models, the stresses are commonly evaluated using the Von Mises formulation.

back to part 1 - Design to part 3 - Thermal Analysis

Copyright © REMOSA spa 1998-2003 Last updated on July 1, 2003