Load Case - Displacement Stress Range

[saulocunha]

I have the following load cases:

L1: W+D1+T1+P1 OPE ( THE HOT OPERATION LOAD SET )
L2: W+D2+T2+P1 OPE ( THE COLD OPERATION LOAD SET )
L3: W+P1 SUS ( SUSTAIN LOAD )
L4: L1-L3 EXP ( EXPANSION IN HOT OPERATION )
L5: L2-L3 EXP ( EXPANSION IN COLD OPERATION )
L6: L1-L2 EXP (DISPLACEMENT STRESS RANGE FOR EXPANSION STRESS CALCULATION)

So, I have some doubts.

In the standard B31.3 says that I have to calculate the "displacement stress range" to ensure that the stresses are not above the acceptable 0.8 SA.

- First: The Case 6 represent correctly the case for the displacement stress range?
- Second: If so, how caesar calculate this? I have to put something in case 6 to CAESAR understand that in this case the stresses cannot exceed permissible 0.8 SA?

Thank you very much my friends.

Regards,

Saulo Cunha

 

[C2it]

Why are you quoting 0.8SA as a B31.3 allowable stress ??

The usual allowable is SA = f(1.25Sc + 0.25Sh)

To get the full stress range you could combine L4 and L5.

 

[saulocunha]

We need to check the Severe Cyclic Conditions. I work in WHITE MARTINS, It's a Praxair's Company and we have a standard that say something like that:

Use L6: L1-L2 EXP (DISPLACEMENT STRESS RANGE FOR EXPANSION STRESS CALCULATION) for severe cyclic service, because severe cyclic service requires special considerations for pipe material, weld X-rays and construction procedures. Therefore to allow use of the standard pipe specifications and welding standars, limit the maximum stress to less than (0.8 SA).

ASME B31.3

Severe Cyclic Conditions: conditions applying to specific piping components or joints in which SE computed in accordance with para. 319.4.4 exceeds 0.8SA (as defined in para. 302.3.5), and the equivalent number of cycles (N in para. 302.3.5) exceeds 7000; or other conditions
that the designer determines will produce an equivalent
effect.


So, what do you about it?

Thank you very much for your answer.

Regards,

Eng. Saulo Cunha

 

[C2it]

It' a company standard, not part of B31.3 which does not retrict stresses to 0.8SA, merely requires some additional work.

Get someone in the company responsible to sort it out.

 

[saulocunha]

I know, but B31.3 say this:

"Severe Cyclic Conditions: conditions applying to specific piping components or joints in which SE computed in accordance with para. 319.4.4 exceeds 0.8SA (as defined in para. 302.3.5), and the equivalent number of cycles (N in para. 302.3.5) exceeds 7000; or other conditions
that the designer determines will produce an equivalent
effect."

So, I understand that we have to keep the stresses below the permissible 08SA. What do you think about ? And how can I use this information in CAESAR to ensure this assumption ?

Thank you again.

Regards,

Eng. Saulo Cunha

 

[C2it]

See Dave Deihl's reply in the Caesar II (Intergraph) forum.