Creating NPT Connections for Piping Fittings
Last Updated: May 7, 2007, By:LB
The best way to analyze NPT threaded piping fittings using FEA methods is with the pipe included in the analysis. Pressurizing the pipe transmits realistic stresses to the fitting body. Anchoring a pipe instead of the fitting produces much more realistic stresses and deflections.
Manifold block with 2 attached pipes.
Construction of the Pipes:
NPT Hole put into a block with the SolidWorks hole wizard.
Reference geometry plane created through the center of the hole.
Edges of the hole “Converted Entities” (highlighted in magenta) used as the basis of a sketch. Use a pipe chart for the wall thickness. The outside diameter of the hole matches the outside diameter of the pipe.
Part is revolved but not merged.
Repeated for the other connection, only the pipe is capped.
All inside surfaces are pressurized. The end of the green pipe is anchored. The pipes and body are bonded.
Two commonly missed areas (magenta circles) these two surfaces are hidden, but must be pressurized to balance the fully pressurized face on the end of the pipes (blue circles). When all the internal areas are properly selected, the reaction forces will be correct.
CosmosDesigner stress plot showing greatly magnified displacement of all components. The pipes are long enough because there is an area along each pipe that is straight (magenta ovals).
Hiding the pipes allows the stresses and deflections for the body to be seen.
Any attempt to anchor faces or edges on this model would alter the deformed shape and the stresses measured. This method of including the pipes is simple and realistic.
This analysis method does not include the effects of thread shear stress on the connections. This can be calculated using Machinery Handbook formulas.