Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: Calculations Subarea: Original Author: Bentley Technical Support Group Comment, Questions, and Answers about ASME B31.4 code calculations in AutoPIPE Item #1: Question, We don't understand the way the expansion stress is checked according to the last revision of ASME B31.4, because we don't understand the resulting allowable stress: based on paragraph 403.3.2 of ASME B31.4 it should be as below, but it doesn't appear to be applied in AutoPIPE. Further, in AutoPIPE online manual (toolbar) the expansion stress is still the same of very old releases (it is referred to a paragraph not more available in ASME B31.,4). it will be very appreciated if You give us an explanation on how AutoPIPE calculates the allowable expansion stress for ASME B31.4 Ed. 2012. Answer: For B31.4 (2009 and higher) AutoPIPE does calculate the unrestrained expansion allowable as per clause 403.3.2 explained below for AutoPIPE: SA=f[1.25(Sc+Sh)- SL] Where: SA = Allowable expansion stress f = Fatigue factor (defined as "Range reduction factor" on Result Model Options dialog) Sc = 2/3 * Sy (Sy is the minimum yield defined on Pipe Properties dialog) Sh = 2/3 * Syt (Syt is the yield value at each temperature case, updated on pressure and temperature dialog) SL = Sustained stress for unrestrained lines Item #2: Question: For ASME B31.4, why are the fields "Use nominal thickness" and "Use nom. Thk. for Hoop" unchecked in AutoPIPE V8i 09.06.00.15? Answer: This is correct and our implementation is inconsistent with our online help as well. A new enhancement ( TFS-75309 ) has been logged to update the online help. Item #3: Question: Using AutoPIPE V8i 09.06.00.15, with ASME B31.4, on the input grid Piping Restraint tab shows, stress equation column: On Tools> Model Options> Results> : Answer: The Xtra Data option Piping Restrain is only used to control which combinations are displayed on the output report, result grid and interactive scan. AutoPIPE classifies certain equations as Restrained, and others and unrestrained and performs the calculations accordingly. When the Result Model Option "Use rest. long. code eq." option is checked, AutoPIPE then uses the exact code equation to calculate the Longitudinal stress regardless of the support configuration and actual forces. Item #4 If I follow the above information, I could set "Restrained" and don't check "Use rest. Long. Code eq." without any warnings … this seems to be illogical. Answer: The restrained / unrestrained / Equivalent / Show Both Xtra Data options are only used for controlling which code combinations shall be displayed on the output report. These options do not affect the calculations performed for the combinations. The Result Model Option "Use rest. Long. Code eq." however, decides how the longitudinal stress values are calculated for restrained code combinations like "Rest-Fun" and "Rest-Env". If this option is checked, the axial expansion stress would be calculated as prescribed by the code i.e. E*alpha*dT regardless of the pipe being fully restrained or not based on actual support (soil) stiffness values. If however, this option is unchecked, then AutoPIPE uses the actual thermal forces developed due to the actual restrain conditions. Also, if checked, AutoPIPE will use a value of v*Hoop stress for calculation of longitudinal pressure stress. Item #5 What is the procedure to apply if we want to consider the Von Mises (maximum distortion energy theory) combination? Answer: To be able to see all the combinations, use the XTRA DATA option "Show Both" to enable AutoPIPE to show all types of equations. Also, using Equivalent will allow user to see the equations as were available in earlier editions like B31.4 (2006). Hope this helps. Please thank the user from our side for taking the time out to point these issues out to us, we appreciate that. Item #6 Request an option to choose Von Mises criterion or Tresca criteria since ASME B31.4-2012 admits to use both: Answer: You may be able to do that today. The default code category "Tensile" generates the results based on Tresca criteria. However, if you change the category for the default Tensile code combination or create a new code combination with category selected as Von mises, you would be able to get your Von mises criteria stresses (with no allowable associated however). To be able to do the same with the restrained functional category, you may use the Total Stress option on the Result Model Options to get your stress results based on either Von mises or Tresca criteria. Item #7: why is the code allowable for ASME B31.4 - 2012 is different from B31.4-2009 for Stresses Due to Sustained Loads? A nswer: According to AutoPIPE help section: Reference Information> Code Compliance Calculations> ASME 31.4 2012> A. Stresses Due to Sustained Loads allowable: "AutoPIPE reports Sl, and the allowable stress (0.75×Sy), where Sy is the specified minimum yield strength." B. According to ASME B31.4 code: Stress Values for steel pipe during operation shall not exceed the allowable values of table 403.3.1-1 as calculated by this chapter. 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! Stresses Due to Sustained Loads
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