Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: Modeling Subarea: Original Author: Bentley Technical Support Group Attention: Please see the following AutoPIPE help section: Help Contents Contents Tab Modeling Approaches Modeling Approaches This help has been provided in order to give users ideas for modeling typical piping arrangements. The steps shown in each example should not be taken as the only method available to create models. In addition, the intent of the examples is to present ways to create adequate models of specific piping components for analytical purposes. Anchors Bends Cuts Flexible Joints Frames Hangers Nozzles Pipes Reducers Rotating Equipment Supports Tees Valves Vessels Comments, Questions, and Answers: Item #1 For flexible joints, how to apply define coeffcient of thermal expansion, and where it is defined? Answer: The flexible joint will have an effect on the thermal movement of the pipe based on the stiffness specified on the flexiable joint dialog screen. In addtion, translation of theremal movement can be accomplished by adding a axial restraint across the flexible joint. Anotherwords, a flexible joint itself does not undergo any thermal expansion/contraction i.e. no thermal properties are applied to the joint itself. As seen in the online help: Flexible joints are modeled as a one-point lumped spring expanded into a two-point spring element. Item #2: Where can I input the material of the flexible joint? Answer: AutoPIPE lets the user define the stiffness terms of the flexible joint directly so no material property definition is needed. Therefore the following 4 statements are true for Flexible Joints: A. No thermal expansion is applied to the joint B. No material property is applied to the joint. C. Code stress color plot does not apply to flex joints. D. Hoop stress or other code calculations does not seem to be calculated for flexible joint. Item #3: Wh en modeling the Tied-belows example using Tie/Link supports. The tie/links allow the pipe to move father appart than the length of the tie/link. Answer: Correct a tie/link support does not maintain arc swing length. However, they do maintain the distance between tie rod ends where the main control function is to maintain the flanges parallel. No program including Caesar will arc tie rods and even if it does would be insignificant change in the expansion joint behavior. Item #4: Can you send me an example model of a bellows than what is available in the online help: Answer: yes, see the following: http://communities.bentley.com/products/pipe_stress_analysis/m/pipe_stress_analysis_gallery/260260.aspx Item #5: How do I model Flex / Braided hose: Answer: Flex hoses are typically so flexible that it is like a break in the pipe with no transfer of force or moment therefore a simple axial bellows with low stiffnesses in all degrees of freedom. Unless the the manufacturer can provide some stiffness values. Suggest using 1 or mulitple flexible joints back to back with tie rods as required. If no stiffness is given, I would recommend using a zero stiffness for the flexible joint, but due to possible instability, you would need to provide a small non-zero value, e.g. 1 lb/in. I would also recommend that you set the pressure area to zero. You may be able to check for bending radius if you calculate an equivalent angle. Frame elements may be used, but flexible joints are easier in this case. For frame you would need to enter non-standard section properties instead of stiffness. Note: remember that AutoPIPE cannot handle large deformation and forces/moments are based on original un-deformed geometry. Item #6: When modeling a flexible hose, what is the most realistic way to model the curved flex hose. Using 1 flex joint, 2 flex joints or many flex joints? Answer: Keep in mind what a flexible hose is doing, as mentioned above "it is like a break in the pipe with no transfer of force or moments". Therefore you can model it using a single flexible joint or using multiple flexible joints where both approaches would use very low Axial, Bending, and Shear stiffness values. Assuming the stiffness values used are very low, then both modeling approaches would be valid. The only major difference between them would be the CG location of the hose. Depending on the hose size, it may need to be considered. Thus giving a slight edge to using multiple flexible joints when modeling a hose (assuming you know the exact path of the flexible hose during operating load cases). Note: 1. When inserting a flexible joint be aware of the stiffness directions and how that affects the connected pipe. Example, using a single flexible joint, axial stiffness is acting along the line of the connected points. Using low values as mentioned above, should not affect the results very much. However, if for what ever reasons axial stiffnesses are higher, it could affect how the connect pipe moves during load case combinations. 2. If modeling multiple flexible joints back to back. Consider adding a short bend pipe between the joints to reduce the occurence of warnings (i.e. W726-8: Kink in straight run ...). Item #7: On the flexible joint dialog screen, "Pressure thrust area" From the online help: This is the effective cross section area, usually based on the mean diameter of the convolutions of the expansion joint. It is multiplied by the internal pressure to obtain the axial thrust due to internal pressure. This thrust is used if a rigorous pressure extension analysis is requested." If I understand this text correctly, this thrust means a force that has to be applied to the pipe at both ends of the expansion joint due to the pressure in the pipe. The direction of this force is axial and away from expansion joint. Please confirm my understanding. Also, how do perform a "rigorous pressure extension analysis" in AutoPIPE Answer: Correct - a force is applied in each direction. Please see the following AutoPIPE help section: Help Contents Search Tab enter "rigorous pressure" (include the quotes), press List Topics button, double click on the " Include Axial, Pcase in Sustained" topic from the list provided to see more information on this option. See Also Bentley AutoPIPE External Links Bentley Technical Support KnowledgeBase Bentley LEARN Server Comments or Corrections? Bentley's Technical Support Group requests that you please submit any comments you have on this Wiki article to the "Comments" area below. THANK YOU! Include Axial, Pcase in Sustained
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