Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: Calculations Subarea: Original Author: Bentley Technical Support Group Comments, Questions, and Answers about DNV piping code calculations in AutoPIPE Item #1, Question: The problem is: by calculating the Von Mises stress in a separate way, the result it is different respect to the automatically calculated ASD. Why? Answer: The ASD check uses the literal equations presented in DNV-OS-F101. For each point, the combined bending moment M (comprising of in-plane and out-plan moments), and combined pipe wall force N (combined axial force at the location) are used for calculation of longitudinal stress. The hoop stress is also calculated as outlined in DNV-OS-F101. The above results are then combined to calculate the effective stress as per the equation provided. The results for the ASD check will be different from those of Von Mises tress calculation, which is calculated differently. Item #2, Question: In the AutoPIPE on line manual (help/contents/code/DNV 2012/ASD) there are references to formulas numbered as per DNV 2010, not as per 2012 edition. At the section 5-F200 of DNV 2012 a new definition of bending is presented, that is not reported in AutoPIPE manual. Answer: Online help shall be updated to reference the correct equation numbers. Item #3, Question: The AutoPIPE (automatic) calculation of the ASD is lower than the hoop stress and that is not possible! At bend flexural deformation occurs due to thermal/pressure elongation: the bending determines tensile and compressive stress at the pipe section. Together with the hoop stress, Von Mises calculation shall also consider the compressed fiber of the pipe section (as required in the of bending moment definition in section 5, F200, of DNV 2012). Answer: Still under investigation, however, it seems like there are a couple of differences between Von mises and DNV ASD check: 1. ASD check does not use stress intensification factors, whereas Von mises calculations do take in to account the SIF factors 2. It seems that AutoPIPE is not calculating the correct maximum compressive/tensile bending stress locations when calculating ASD check for DNV 2012 3. This may require some changes in the program to be corrected, Von mises category may be used as a work around as the user is currently doing Item #4, Question: Difference in values of general stress results and user Von mises results Answer: DNV code von mises equation forces program to use effective section modulus to be used for DNV, however, the general stress report does not use effective section modulus which can be attributed to the difference. Item #5, Question: The results for DNV code combinations Collapse and Prop Buck are 0.00 or very small, why? Answer: Typical reason for 0.00 or low values: 1. Be sure to check that the node points are actually located below the Water surface. View Show options "Water Surface & Sea Level" is checked on, press OK button and confirm node point is with int he blue are of all the waves specified in the model. Only those points below the water surface, will have calculated values 0.00. 2. The model units may a limitng factor, with the "DNV-OS-F101-INITIALMODEL.DAT" provided in the Example folder (C:\Bentley\AutoPIPE V8i SELECTseries\Examples), change the Tools Model options General units from SI to English and re-run the analysis report: 3. Please see the following AutoPIPE help section: Help Contents Contents Tab Reference Information Code Compliance Calculations DNV 2012 Collapse Limit (DNV - 2012) Equation 5.14, Code stress value is calculate based on Pext - Pmin, The external pressure at any point less minimum pressure defined in DNV 2012 options dialog will be reported for that combination as the calculated pressure. Confirm the following dialog settings are correct: Load Wave Tools Model Options DNV 2012 Result Options Load Buoyancy Note: Check to be sure the water level / ground elevation on the Wave, Wind, and Buoyancy dialog screens all agree. They could have different elevation values that would cause the respective load to be applied to the model incorrectly. To keep things simple, may consider using the Vertical axis location = 0.00 as the water / ground elevation and locate the piping arrangement accordingly. Thus making it easy to understand that anything above the Vertical axis (default Y) = 0.00 will be exposed to wave or wind loads accordingly. 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!
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