Pipe Stress Analysis using Ansys APDL Command Method
Sample 3d Model Considered
Piping Line Diagram
Piping Inputs • • • • • • • • • •
Unit System: British (Inch) Piping Analysis Standard: ANSI B31.1 Young Modulus: 30e6 Thermal Expansion: 8e-6 Density: 0.283 Pipe Dimension: 8 inch standard Drag= 0.2 psi in –Z direction at any height (Y) Temperature= 200 deg. Internal Pressure: 1000 psi Spring stiffness: 1e4
Explanation of The piping Diagram As can be seen from the figure the piping diagram shows a bend supported with spring hangers, a metered bend and a T Connector finally leading to two branches. Student need to know what is a metered bend and its significance
What can Ansys Do…… • Creates a line model of a piping network using straight pipe (PIPE16) and curved pipe (PIPE18) elements. Node and element geometry is defined in terms of incremental run lengths and bend radii, rather than in terms of absolute coordinates. • Automatically calculates tangency points for bends. • Relates standard piping designations (such as nominal diameter and schedule) to geometric values. • Assigns pipe specifications to element real constants. • Calculates and assigns flexibility and stress intensification factors based on the pressures and the temperatures specified in the pipe module before the creation of the piping elements as appropriate for each element type. The flexibility factors will not be changed automatically if the pipe pressures or temperatures are subsequently revised. • Determines drag pressure loads from a pressure vs. height relationship
Boundary Conditions Restrains fixed arresting the 6DOF at 3 places- This can be places which runs to the equipment as well- in such cases we might have reaction forces in some DOF hence this point to be considered. You have provisions to assign all type of pipe supports like hangers which cpould be assigned in addition to all pipe connections. You can apply temperature and operating pressure as loads which are infact the loading for any piping flexibility. In addition insulation, corr allowance etc are further options
Procedure • /FILNAM,SAMPLE • /TITLE,SAMPLE PIPING INPUT • /UNITS,BIN ! A reminder that consistent units are British inches ! • /PREP7 ! • Define material properties for pipe elements MP,EX,1,30e6 MP,ALPX,1,8e-6 MP,DENS,1,.283 PUNIT,1 ! • Units will be read as ft+in+fraction and converted to ! decimal inches • PSPEC,1,8,STD ! 8-inch standard pipe • POPT,B31.1 ! Piping analysis standard: ANSI B31.1 • PTEMP,200 ! Temperature = 200 deg
Procedure Contd….. • PPRES,1000 ! Internal pressure = 1000 psi • PDRAG,,,-.2 ! Drag = 0.2 psi in -Z direction at any height (Y) • BRANCH,1,0+12,0+12 ! Start first pipe run at (12",12",0") • RUN,,7+4 ! Run 7'-4" in +Y direction • RUN,9+5+1/2 ! Run 9'-5 1/2" in +X direction • RUN,,,-8+4 ! Run 8'-4" in -Z direction • RUN,,8+4 ! Run 8'-4" in +Y direction • /PNUM,NODE,1 • /VIEW,1,1,2,3
Procedure Contd….. • • • • • • •
EPLOT ! Identify node number at which 2nd run starts BRANCH,4 ! Start second pipe run at node 4 RUN,6+2+1/2 ! Run 6'-2 1/2" in +X direction TEE,4,WT ! Insert a tee at node 4 /PNUM,DEFA /PNUM,ELEM,1 EPLOT ! Identify element numbers for bend and miter inserts • BEND,1,2,SR ! Insert a "short-radius" bend between elements 1 and 2 • MITER,2,3,LR,2 ! Insert a two-piece miter between elements 2 and 3 /PNUM,DEFA
Procedure Contd….. • /PNUM,NODE,1 ! Zoom in on miter bend to identify nodes for spring hangers • /ZOOM, 1, 242.93 , 206.62 , -39.059 , 26.866 • PSPRNG,14,TRAN,1e4,,0+12 ! Insert Y-direction spring at node 14 • PSPRNG,16,TRAN,1e4,,0+12 ! Insert Y-direction spring at node 16 ! List and display interpreted input data • /AUTO • /PNUM,DEFA • EPLOT • NLIST • ELIST • SFELIST • BFELIST
E List Command Results • Element List, PIPE16 and PIPE18 elements were used (Infer the table)
Node List Command
Load Listing- Pressure
Load Listing- Temperature
Post Processing- Displacement • Displacement
Displacement Contd….
Look into the maxm nodal diplacement value( check the local/global direction) if this exceeds the limit alter the length, bend radius etc and recheck it
Post Processing- Stress Intensity Factors(SIF)
SIF Contd….. SIF Is very important in piping design and flexibility analysis. The SIF has to go along with ASME 31.1. The analysis shows a SIF Value of 3.465 @ Element 11 which correspond to node 14 and 15. Identify this and compare with code compliance, this might be a bend, a T or some thing else. Please read ASME SIF 31.1 Along…….
Post Processing- Bending Stress
Bending Stress Contd…….. This has to be compared with 31.1 for code compliance. For this we will have to go for code compliance on each element.
