| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Environment: | N/A |
| Area: | Settings |
| Original Author: | Bentley Technical Support Group |
| Date Logged & Current Version |
March. 2017 11.00.00.22 |
Problem:
How does "Use corroded thickness in all analysis" on Edit Model options dialog different from "Use nominal thickness" on Results Model Options dialog?
Solution:
The Edit Model Option "Use corroded thickness in all analysis" setting is often confused with Results Model Option "Use Nominal Thickness" setting. These are 2 complete different settings that affect the application in different ways.
"Use corroded thickness in analysis"
One of the initial analyses conducted by AutoPIPE occurs within a section of the program known as the pre-processor. During this phase, the program divides the entire model into stiffness equations, which are subsequently incorporated into what is termed a Stiffness Matrix, solved simultaneously. This configuration determines the wall thickness utilized in the resolution of these matrices for the calculation of displacement, forces, and moments. In addition, this configuration not only impacts the static analysis stiffness matrix but also the dynamic analysis stiffness matrix.
In some cases, enabling this setting may result in reduced forces and moments; however, the majority of piping codes require the use of nominal thickness for flexibility analysis. Following any modification to this setting, one may consider it essential to re-analyze the model.
Note, see AutoPIPE help for details on how the Corroded thickness is calculated.
Example: Cantilever beam, ASME B31.1, 2020, units = AutoPIPE, OD = 12 in, sch = STD (0.375 in), Corrosion Allow = 0.2 in. material = A376-TP321H, Press = 0 psi, Amb Temp = 70 deg f, Insert Anchor at 0,0,0, insert run DX = 10 ft, at A01 insert concentrated force (load case = U1) FY= -10000 lbs.
Set up analysis set #1, with GR and U1.
By default the Use Corroded thickness option is Disabled, therefore the analysis is using the full pipe wall thickness, 0.375 in, Thus the displacement for U1 = -0.744 in.
Next, modify Edit Model option to enable "Use Corroded thickness in all analysis", rerun the analysis,
Question: What would be the expectation of the displacement, more or less than before?
Answer: The stiffness of the pipe would go down, therefore it would be more flexible or displace more downward.
The new displacement of node A01 with this option enabled is Dy = -1.521 in.
"Use nominal thickness"
This setting does not affect the calculations of moments. The input in this field determines which pipe wall thickness value is used in stress calculations in the Post processor. After the Force and Moments have been computed, the stress are calculated.
In conclusion, "Use corroded thickness in analysis" enabled would impact everything; Forces, Moments, Displacements, to be more flexible in both Static and Dynamic analysis. However this setting does not impact the Code calculations. That job is reserved for the "Use nominal thickness" and " User nom, thk for Hop" options.
See AutoPIPE help for complete details on these settings.
See Also
Tools> Model Options> Edit settings