TORSION IN SL STRESS

As given in Caesar II on line documentation :
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Add Torsion in SL Stress
Some piping codes include torsion in the sustained and occasional stresses by explicitly including it in the stress equation (i.e. B31.1), and some don't include torsion in the sustained and occasional stresses by implicitly calling for "longitudinal stresses" only (i.e. B31.3). Setting the Add Torsion in SL Stress directive to Yes forces CAESAR II to include the torsion term in those codes that don't include it already by default. Setting this directive to Default causes CAESAR II to use whatever the currently active piping code implies. In a sustained stress analysis of a very hot piping system subject to creep, it is recommended that the user include torsion in the sustained stress calculation via this parameter in the setup file.
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As given for hot piping user shoould include torsion in sustained stress calculation. then what is criteria for selecting very hot piping. means lines having temp above 450 deg C should be considered as very hot piping ?
Means i want to know what is temperature range should be set to include torsion in sustained stress calculation.

if anyone knows regarding this then i request to please explain anbout it.

thanks in advance.

regards,
ajay

The statement indicates to use Torsion in sustained stress when the temperature for the material is in the creep range.
For the temperature you can refer ASME Sec.III Sub.NH App.T Table T-1323.
As per this table, the allowable stress values becomes time dependent above a particular temperature which could be called as the temperature when creep initiates....

For 21/4Cr-1Mo ---- TEMP = 427 deg.C
SS304 ---- TEMP = 509 deg.C
SS316 ---- TEMP = 544 deg.C
Alloy 800H ---- TEMP = 573 deg.C
These temperatures are indicative...

OR

If you see the allowables indicated in B31.3 App.A, you will find a sudden drop in allowable stress above certain temperatures. This is the indication of Creep....hence that can be used as temp above which you can use Torsion in SL stress.

Also read B31.3 Code case-178, which indicates to use Torsion in SL Stress but it has expired on May 1, 2008.

Regards,

Suraj

Code Case 178 was scheduled to expire on 1 May 2008 but, before that date, ASME removed the expiry date.

It is still current. You will find it listed (without expiration) in the back of B31.3 - 2008.

CAESAR II does not default to this stress equation. I would suggest that CAESAR II users throw that switch in Config to use Case 178.