PIPE FEA USING ANSYS

1. PIPE FEA USING ANSYS

2. FEA and ANSYS • Finite Element Analysis (FEA) • A numerical technique used for finding approximate solution of physical problems • Only through the use of modern day computers, FEA becomes effective and practical • ANSYS • The FEA software widely used in the industry, one of Hatch’s main FEA software. • Two interfaces: classical and Workbench share the core solvers • Workbench is easy to use, best suited for 3D modeling • Classical is more powerful, gives the user more flexibilities

3. ANSYS Classical

4. ANSYS Workbench

5. FEA procedures

6. Pipe System To Be Analyzed • Long, large diameter, thin walled steel pipes • Lined with refractory and insulations • There is no other external loads except for self weight • The pipes will see thermal growth at start up • The roof of the bins may also move due to thermal expansion at start up

7. FEA decisions • 3D SOLID elements? – the model is too big! • 2D SHELL elements? – possible, but still fairly expensive (in term of computing time and model set up time) • 1D BEAM elements – quick and easy, accurate results for reaction forces and moments, which may be used in hand calculations for welds and guidance for support selections. • Detailed 3D / 2D sub models for Y-pipe section and diverters may be analyzed using the 1D BEAM model results.

8. FEA load cases • The load steps the feed pipes may see: • Erect • Connect pipes to the bins • Start up, temperature going up (max. 200 C) • Production cycles A good understanding of each load step is essential for the success of the analysis!

9. FEA load cases • Load cases for the FEA model: • Run one load case to determine the preload required from the Spring support and size the spring • Room temperature; all support connected except for the expansion joint; gravity load applied • Room temperature; all support connected including the expansion joint; gravity load applied • Uniform max. temperature applied on pipes; all support connected including the expansion joint; gravity load applied; bin roof thermal movements applied

10. FEA for pipes Mesh Visual representation of the beam model “Skeleton” Line Model Beam Model

11. FEA for pipes • Element type • PIPE16 (pipes and flanges): specialized BEAM element • COMBIN14 (expansion joints & spring supports): Spring elements • LINK 10 (cable support, if applicable): tension only link elements • Real constants • Each element is defined by Element Type and a set of real constant values • For example, “PIPE16 and Real constant set 2” tell ANSYS these elements behave like a circular hollow beam, OD=0.4064m, Wall thickness=0.0095m,… • Material properties • Mild steel • Increase the density for the pipes to match the density of pipe+refractory+insulation

12. FEA Results for Pipes

13. FEA Results for Pipes • Displacement in all six degree of freedoms at any node • Reaction forces and moments at any node • Various stress results (bending stress, axial stress, shear stress, von-mises stress, principle stress…) for all elements • Physical properties of the model (volume, mass, moment of inertia…) based on the model geometry

14. Interpreting FEA results • The underline theory for the BEAM model is the same as we use in hand calculations. • The same limitation of BEAM theory applies both in FEA and hand calculations. • Anything weren’t included in this BEAM model from the beginning are not in the results (diverter, Y pipe..)