Please be informed that we are struggling with Autopipe ASD stress checking according to DNV-2012 design code. I made an Autopipe model to do a code stress checking according to DNV. Unfortunately, during verification of Autopipe results I discovered a wrong default parameter setting when the design code of DNV is selected. The Autopipe results for two different parameter settings are presented as the following:
Model-1 (default setting)
Pipe Properties:
Inside pressure = 299 bar
Design code is selected DNV2012 and the Y factor is 0 and P is selected for Long. Pressure (P/A/M/N) (see the following figure) which is the default setting of Autopipe.
Figure-1
The DNV Code Compliance result is shown in the following figure:
Figure-2
As it is clear from the above, the result are as the following:
It is assumed that the above force presented by AUTOPIPE is the effective force according to the definition of DNV-OS-F101. Then I calculated the true wall force, the longitudinal stresses and the equivalent stress according to DNV-OS-F101 as the following:
Figure-3
With comparing my calculations with the Autopipe results it is clear that the maximum longitudinal stress and the equivalent stress are not matching!
Model-2
Model-2 is same as Model-1 and just parameter 'A' is selected for Long. Pressure (P/A/M/N) (see the following figure)
Figure-4
Figure-5
Comparing the above Autopipe results with my calculations (Figure-3). It shows that the results are almost the same.
Conclusion
From the above results it seems that the default setting of Autopipe for DNV code checking is wrong. As it is clear from Figure-2, the equivalent stress is under estimated based on the default setting of Autopipe which could cause a lot of problem. Bentley is kindly requested to review this email to approve or make comment on the following statement:
Please be informed that we should make a decision ASAP that which parameter setting is matching more with DNV-OS-F101 requirements to avoid any delay in construction. So, I am looking forward for receiving your response very soon.
Thanks in advance for your swift reply.
Hello M_kh,
After selecting a particular piping code and year on the General Model options dialog, the program will automatically grey out some values and adjust some settings to a default value. These default settings may be adjusted at any time by the user and the settings saved under Tools> Model options> Save defaults command (see AutoPIPE help for full information about this feature.
Based on information above, you are requesting that the Results Option> Long Pressure (P/A/M/N) default setting be changed from P to A when using DNV 2012. I have asked the development team to review this default change and to respond with their findings. In order to avoid any delay in construction, suggest that you change this and other setting as needed for your modeling scenario.
Thank you for your suggestion and detailed write-up. It will be helpful in our review.
Regards,
Mike DattilioBentley Product Advantage Group AnalystAutoPIPE Product Line Bentley Systems, Inc.===================================================
Dear Mike,
Thanks for your reply. However, Bentley is requested to make clear which parameter setting shall be selected for 'Long. Pressure (P/A/M/N)' according to DNV-OS-F101 requirements. If parameter setting of 'A' shall be selected then it makes sense to be raised in your website and communities for all the users. For example we are checking the Autopipe models of other companies and we should have a reference to advise them for selecting a correct parameter setting.
In addition, Please be informed that I have also a problem with 'Y factor' in 'Result Model Options dialog'. With changing the Y-factor, ASD check results according to DNV are changing. It seems the Y-factor shall be zero for calculating the hoop stress according to DNV. However, it is not clear in AUTOPIPE help manual that the value of 'Y factor' can have impact on the DNV code compliance results. The reason of confusion is 'DNV 2012 Result Options dialog' . In AUTOPIPE help it is mentioned " The DNV 2012 Result Options dialog puts together all the factors used in the DNV-OS-F101 calculations in a single dialog.". However, there are other parameters like Y-factor and 'Long. Pressure (P/A/M/N)' in 'Result Model Options dialog' which could cause changing the results of the DNV code compliance check.
Mehdi Khanlari