ASME B31.1 - Liberal stress

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r2user_0209
Beiträge: 11
Registriert: Di 28. Feb 2012, 15:16

ASME B31.1 - Liberal stress

Beitrag von r2user_0209 »

Hi Rohr2Support

I have created a new model using ROHR2 31.2a using ASME B31.1 as stress code.
Now I see 2 SE equations, one without liberal stress and one with liberal stress.
Here is an extract from the stress analysis:
Pt 11 Line 1 v Da= 219.1 mm s= 7.1 mm (TFS ) Butt welding tee
Line 1 n Da= 219.1 mm s= 7.1 mm
Line 2 n Da= 168.3 mm s= 5.6 mm

Na Gl P S(P) Ma Mb,c i S(M) S-sum S-allw Util
(bar)(N/mm2) (kNm) (kNm) (N/mm2)(N/mm2)(N/mm2) (%)
01 SL v 25.0 17.4 1.313 2.6 10.4 27.8 106.2 26
01 SL n 25.0 17.4 1.176 2.6 9.3 26.8 106.2 25
01 SL n 25.0 16.9 0.249 2.6 3.2 20.2 81.9 25
02 SE v 21.555 2.6 227.9 227.9 201.6 113*
02 SE n 15.433 2.6 163.2 163.2 201.6 81
02 SE n 9.220 2.6 160.3 160.3 195.5 82
03 SE v 21.555 2.6 227.9 227.9 280.0 81
03 SE n 15.433 2.6 163.2 163.2 281.0 58
03 SE n 9.220 2.6 160.3 160.3 257.2 62
04 SOL v 25.0 17.4 1.313 0.834 2.6 17.0 34.5 122.2 28
04 SOL n 25.0 17.4 1.176 0.646 2.6 14.5 31.9 122.2 26
04 SOL n 25.0 16.9 0.249 0.972 2.6 15.9 32.8 94.2 3
The one without the liberal stress is overstressed.
Do I have to consider this equation?
Does the new edition of ASME requires this calculation?

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

Re: ASME B31.1 - Liberal stress

Beitrag von rohr2support »

Dear Rohr2 User

In version 31.2a we have added the generation of the SE equation without liberal stress by default so that we have similar results as the S3 and S4 equations from the EN13480-3 code.
The equation without liberal stress can be used to see how much pure thermal stresses you have.
As for the EN13480-3 the S3 equation ASME B31.1 does not require that the equation without liberal stress must be met.
It is sufficient to verify the stress equation including liberal stress.
Nevertheless it is often usefull to know, whether pure thermal stress alone will stay "elastic" on its own or if there are some
areas (which are overstressed in S3 equation) that are elastic after shakedown, in other words there may be some plastic deformation in the first thermal cycles.

You can switch of the generation of the equation without liberal stress using the button in the stress menu:
No_S3.png
Best regards

Rohr2 Support
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