flexMen,

Trust me, my well experienced and educated colleagues know their stuff. Regarding you latest post, where you ran four separate models - two of them would not be a valid analysis for the sustained stresses because you wouldn't be be checking against the correct Sh.

I think the part that you are not quite getting is that your system has to satisfy the sustained stress requirement *at temperature*. As such, your operating temperature is what governs the Sh value.

You make this comment:
"But I think that there would be 3 sustained cases and every sustained case compared to corresponding Sh."

Now, for simplifcation, lets assume that none of your supports lift off. In that case, your calculated sustained stress is going to be the same for each of your temperature cases. Comparing them in two cases to a higher Sh because the temperature is lower provides no useful information, becuase those same calculated stresses still have to be lower than the minimum Sh, which is set by the highest operating temperature. If you system can regularly see a temperature, your sustained stresses have to be good for that Sh.

Now, as for the business of Occasional stresses, you say as your opening line:

"If I realize the calculation of those 3 cases of load in 3 different files, the verificacion of occasional stress code, IS CORRECT."

Actually, no, it isn't, for the same reason I gave above with regard to the sustained stresses. Two of your three files are not valid for calculating the sustained and occasional stresses because they do not consider the highest temperature that your system will operate at.

Now, here's the big if that I think had been hinted at - if you can justify that your occasional load case can only occur when your system is at T=25°F, then I think you could make a case for checking your occasional stresses based on Sh at 25°F. Quite frankly, I can't think of what kind of loading that would be, certainly niether wind nor seismic. If this is your situation, I'd like to hear it in detail.

Otherwise, you need to consider Sh based on the highest temperature. Let's take wind - it is meaningless to say that your pipe won't be overstressed due to wind load when the pipe is 25°F when it will be overstressed at 560°F. The fact that is "passes" at 25°F doesn't make your design any good. If it fails at 560°F, then it is an inadequate design and needs to be better supported/restrained.