Hi Dave/Richard,

I am confused a bit while reading clause 302.3.6 of B31.3 for occasional cases, it says metal temperature.
So whether we need to add wind , seismic with ope condition in CAESAR II or in design condition?

302.3.6 states that limit to the sum of stresses due to sustained loads and stresses due to occasional loads is 1.33Sh. The reference to metal temperature is with this Sh, not loads (e.g., thermal strain) - the allowable stress is based on the expected temperature during the occasional event.

Thanks Dave for your response.

However, the expected temperature during the occasional event like wind, seismic would be operating & not design.

Is there any reference to above is available in any code etc?

I typically use the design temperature(s) for all cases just to be conservative.

I don't typically have 500F in operating cases to set up the expansion case and then use something like 300F in the operating cases w/ occasional loads.

Vick,

In my opinion,
The B31.3 "design" temperature (and it's coincident "design" pressure) is only used to set the minimum wall thickness.
If I am performing a structural (or stress) analysis of a specific, say, operating "state" of the piping system, I would set my pipe temperature to the metal temperature of the pipe. Para. 319.3.1(a) provides an example with the statement "Values of thermal displacement ... for computing the stress range shall be determined [based on] ... maximum metal temperature and ... minimum metal temperature for the thermal cycle under analysis." There is no mention of "design conditions" here.
Use your line list.
(Here's where things can get sticky ...) Many systems have a higher design pressure/temperature pair than the actual operating pair. Does this mean that an operator can arbitrarily increase operating conditions as long as they remain below design? I'd say yes if the only concern is maintaining the pressure boundary (that wall thickness rule). But this wall thickness concern does not address changing support conditions which may lead to collapse (SL > Sh) or the fatigue life of the line (SE > SA). This is one reason why engineers analyze the "design" conditions - to be sure the system is safe under those (possible?) loads.