hi
i hope this forum is not only for professional but students who they are interested in stress also can participate.
im a doing my college project in piping stress analysis.i could not find any other place to post my doubts better than this,as i know Caesar5 is the software using worldwide for stress analysis.

i went through some stuffs i downloaded form Net and some codes and standard .i cant understand anything in this code as it is not giving direct answer. anyway i learnt lot after a long run ..
after that i got lot following doubts

1)why we are checking sustain stress with hot allowable not with cold allowable, as sustain stress is concurring in installing condition where temperature is atmospheric only ?

2)why we are taking two times of yeild(+2Sy & -2Sy) stress using to make displacement stress range since after yield point material will be plastic state rit?

3)is occasional stress is primary or secondary ?

hope some can shed a light on my question..i hope you can tell me the answer in more practical way..

if dont mind some basic notes on SIF ,Spring,Bellows,Safety Valve

1) The hot allowable is used as the limit for the Sustained case because the "primary stresses" must be below the allowable in all conditions (load cases) that the system may actually experience.

2) Think of it this way - the system can displace heating up (but the stresses must stay below the hot yield), and the system can displace cooling down (but the stresses must stay below the cold yield). This gives twice yield for the total range.

3) Occasional loads are primary - because they are "force based", limited by yield. Exceeding yield leads to collapse.