piping compensator pre-stretching

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Igor55587
Beiträge: 3
Registriert: Sa 24. Sep 2016, 09:04

piping compensator pre-stretching

Beitrag von Igor55587 »

Does anybody knows how can i insert data for pre-stretching of U-shaped expansion compensator in Rohr2 program? Medium is steam, 31bar, 450C and the distance between fixed supports is 80 m. Total length of straight pipe is 1000 m.
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rohr2admin
Administrator
Beiträge: 631
Registriert: Di 13. Sep 2011, 14:03

Re: piping compensator pre-stretching

Beitrag von rohr2admin »

Hi,

you can apply cold springing accoring to the user manual, just select the function "cold springing" and press the "F1" button on your keyboard:
coldSpringing.JPG
The program will lead you to the corresponding chapter in the user manual.
Keep attention, that you will have to create an additional (cold) secondary load case, where only the cold springing exists, no thermal expansion.

We also have a video on our webpage, where you can see the usage of cold springing, it is the "ROHR2: Inserting expansion joints into a piping system using ROHR2":
http://www.rohr2.com/en/downloads.html
https://youtu.be/EiHAyYFKL5M

best regards,
ROHRsupport
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Igor55587
Beiträge: 3
Registriert: Sa 24. Sep 2016, 09:04

Re: piping compensator pre-stretching

Beitrag von Igor55587 »

Hi,

Thank you for answer!
I have one more problem for cold springing.
If I use cold springing for U-shaped expansion compensator, I get worse results using cold springing (125%), than without cold springing (99%). What is the problem?

What is a factor for cold springing in global loads? What difference does it makes?
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rohr2admin
Administrator
Beiträge: 631
Registriert: Di 13. Sep 2011, 14:03

Re: piping compensator pre-stretching

Beitrag von rohr2admin »

Hi,

what exactly gets worse, stress utilization, loads or maybe movements at expansion joints? It is actually not allowed to use cold springing to reduce the stress range at all, please have a look at the manual or the calculation code.

Best regards,
ROHRsupport
Igor55587
Beiträge: 3
Registriert: Sa 24. Sep 2016, 09:04

Re: piping compensator pre-stretching

Beitrag von Igor55587 »

Hi,

Stress utilization gets worse.
Why it is not allowed to use cold springing to reduce the stress range?
If we use cold springing then pipe is under smaller stress in operation load compared to without using cold springing.
If we use cold springing then pipe thermal expansion stays the same (same as without using cold springing), why is stress utilization still increasing?
We think that the program is summarizing thermal expansion and cold springing movements in stress utilization calculation process.

We have basic manual and stress manual and we havent found information about cold springing using conditions.


Best regards,

Igor
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rohr2support
Beiträge: 455
Registriert: Mi 14. Sep 2011, 08:23

Re: piping compensator pre-stretching

Beitrag von rohr2support »

Hi

Stress range is the difference between two stress states. If you shift both stresses in the same direction (e.g. by pre-stretching) the stress difference does not change.
If you include pre-stressing in a pipe stress calculation with a lot of friction, you may even get higher stresses, as the sign of the friction forces changes between heating up and cooling down.
This is the reason why we included the "Shutdown" case as one of the predifined load cases in a new ROHR2 project so that you can detect what impact the change of sign for friction forces may have on the system.

Best regards

ROHR2 Support
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