PIPE FEA USING ANSYS

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

ANSYS Classical

ANSYS Workbench

FEA procedures

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

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.

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!

FEA load cases Load cases for the FEA model:

0 Run one load case to determine the preload required from the Spring support and size the spring

1. Room temperature; all support connected except for the expansion joint; gravity load applied

2. Room temperature; all support connected including the expansion joint; gravity load applied

3. Uniform max. temperature applied on pipes; all support connected including the expansion joint; gravity load applied; bin roof thermal movements applied

FEA for pipes

“Skeleton” Line Model

Visual representation of the beam modelBeam Model

Mesh

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

FEA Results for Pipes

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

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..)