Dear Dave/Richard,

As per Latest ASME B31.3 code, Definition of SL is as follows:

SL = stress due to sustained loads; in systems where supports may be active in some conditions and inactive in others, the maximum value of sustained stress, considering all support conditions, shall be used

By default, alternate sustain cases also prepared based on the temperatures in C-II.

My query is that why alternate sustain cases are not mandatory in C-II ?

Regards,
Bhavin Shamalia

Caesar II is not a Design Code, or a Global/Authority Standard.

It is a dedicated/professional Software for Pipe Stress Analysis purpose, and it MAY be used in accordance with several Internationally recognized Design Codes or Standards.

(NOTE. You'll NOT find any such kind of Software to be mandatorily used in Industry. On a specific Project, there is an agreement between Owner/Client and Contractor/Consultant what Software to be used.)

Now, what Design Code and what Design Basis you have to apply, that is definitely NOT Caesar II purpose or responsibility. The software has a wide range of configuration possibilities.

It's YOU, as ENGINEER and software USER, to DECIDE what Design Basis to employ.

To go now to your specific inquiry, Alt-SUS loading cases are RECOMMENDED by Caesar II within Static Loading Cases definition spreadsheet - it's the 3rd Button from Right to Left at Top-Left Spreadsheet Area.
The recommended Alt-SUS cases depend on what kind of OPE-rating Loading cases you've defined.
BUT it's your task and responsibility to develop the loading cases to comply with your Design Code and Project Design Basis.

See User Guide Manual for more details.

While CAESAR has made it easier to perform these checks, the software has no way of knowing if each temperature case should be interpreted as a sustained case.

For example, if a given temperature is a result of 5 levels of failure and would only be expected to last for a few hours, the end user may elect to not treat it as a sustained case.

If CAESAR now mandated everything to be a lift-off case, then the engineer's freedom to control the analysis is removed.