Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: Analysis Subarea: Original Author: Bentley Technical Support Group Comments, Questions, and Answers related to hanger selection in AutoPIPE: Attention: To better understand AutoPIPE's Hanger Selection analysis procedures, please see the following AutoPIPE help section: Help > Contents> Search Tab> enter "Design Hanger Selection Procedure" (include the quotes), press List Topics button, double click on the selected topic from the list provided to see more information. Cold Load Design Hanger Selection Procedure Hot Load Design Hanger Selection Procedure Each method has a clear description of the process including a "FLOW CHART" link on each page. Item #1: Note: When only one load case is selected, say T2, the free thermal displacement from thermal case T2 at the spring location node is used for hanger selection at that node. When all thermal cases are selected then the maximum free thermal displacement from all selected thermal cases at the spring location node is used for hanger selection at that node. Item #2: When the support is near (~1m) an anchor. In those conditions the program just suggests a rigid support instead in the spring hanger report. Prior versions would have selected a spring hanger for such a case (we believe). Also note, in cases where a rigid support was required prior versions would have automatically changed them. Answer: Please see the following AutoPIPE help section: Help > Contents> Contents Tab> Reference Information> Hanger Selection Procedure This information will explain how AutoPIPE chooses a spring from the specified manufacture or why AutoPIPE changes the variable spring support to a Constant Spring or Rigid support. In order to force the program to regularly select a Variable/Constant spring, change the Hanger Analysis setting, Rigid hanger criteria = 0.00. However, this may work 90% of the time, but if a spring is located near an anchor location suggest using the "Anchor Releases for Hanger Selection" procedure in AutoPIPE's help section: Help > Contents> Contents Tab> Modeling Approaches> Anchors> Modeling Approaches> Anchor Releases For Hanger Selection. Item #3: Hanger design - do we attach a sign to the cold load ie. - or + ? Depending on the movement whether it should be + or - ? Answer: No, at no time should you enter a -ve value into the spring hanger dialog: Item #4: I thought I fully understood the difference between using the hot load procedure (HLP) and the cold load procedure (CLP) to size a spring hanger, but I guess I was wrong. I have tried running the "WALKTHRU" sample using both the HLP & the CLP, which should give me the same spring size, given the same thermal deflection and GR load from my V-stop run. I end up with two different spring sizes, which has to be incorrect. Answer: No, each procedure is fundamentally different when sizing a spring and therefore the spring size and cold load will be different. As mentioned in the online help: A. Hot Load Design Hanger Selection Procedure: A rigid restraint (V-stop) replaces the hanger for the gravity (GR) load case. The calculated support reaction is the hot load to be carried by the hanger. B. Cold Load Design Hanger Selection Procedure A rigid restraint (V-stop) replaces the hanger for the gravity (GR) load case. The calculated support reaction is the cold load to be carried by the hanger. Example: GR load on the support Dy = -1975 lbs, and T1 movement, Dy = +0.204". Per the Cold Load method, the Hot Load is interpolated to be 1836.6 lbs as shown below: Per the Hot Load method, the Cold Load is interpolated to be 2158.2 lbs as shown below: Note: In the cold load procedure above the Cold Preload for all springs was 1975.0 lbs, however here in the Hot Load procedure, all the Hot load values are 1975.0 lbs. . Again, totally different springs are selected when using the different hanger selection procedures. Item #5: What is AutoPIPE doing when a spring hanger is set for undesigned and ONLY Static analysis is performed. Why are the operating load case all the same values when the Temp settings are so different? Answer: Create a Tools> Model Input listing> with the "Support" sub-report checked ON. See the "Stiff." column of the report, for the indicated spring, and refer to the bottom of the page for the details of . Therefore, the spring stiffness is rigid for GR load case only. Thus, only the GR load case will have a support reaction load while the other load cases that make up the combination (i.e. Temp, Press, etc..) have no support reaction. This is clearly shown by the user's output "Support" sub-report above, Gr = -1975 lbs, T1..Tn = 0, P1..Pn = 0, yields GrT1P1.. GrTnPn = -1975 lbs. Item #6: Why is that there is a big discrepancy between the AutoPIPE Hanger Analysis calculated values and the values that are actually on the spring cans that have been in service for many years. Answer: Highly recommend that you see AutoPIPE online help mentioned at the top of this WIKI page for details on how the program selects a spring hanger. Based on the settings for Hanger Analysis, modeled piping arrangement, support locations, and load cases, AutoPIPE reported 5 different springs hangers that meets the selection criteria for this node location. Furthermore, the program selected the first one spring hanger ( Fig 82, Size 16) to be used in the actual stress analysis. See the hanger report (*.HGR) below: Therefore, the program placed the Cold load (35145.7 N) and Spring Rate (524.8 N/mm) from the hanger selection into the Spring hanger component: So why is there such a large discrepancy, because there is more than one spring that fits the criteria. The Spring Hanger Analysis module selected the first spring can with the longest range and highest spring that satisfies the conditions. As mentioned in the online help: Various hanger selections that meet the criteria are reported in a file named SYSNAME.HGR, starting with the longest range and highest spring rate and finishing with the shortest range and lowest spring rate. The first spring in the list that satisfies the requirements is selected by the program. Another source of possible error is that your piping arrangement and modeling may not match the as-built conditions. Confirm the following: piping properties, contents, load cases, support locations, support types, support gaps, analysis settings, etc... Ultimately, i f you disagree with the Spring Hanger selection, override the automated values with your own to be used during the actual stress analysis. 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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