Expansion Stress come from the highest temperature?

Dear folks,
I have to continue the work of my team, while checking his load case scenarios, I found these:

L4:W+T1+P+H (OPE) note: T1>T2>T3>T4
L5:W+T2+P+H (OPE)
L6:W+T3+P+H (OPE)
L7:W+T4+P+H (OPE)

L8:W+P1+H (SUS)

L36:L4-L8 (EXP) (ALG)
L37:L5-L8 (EXP) (ALG)
L38:L6-L8 (EXP) (ALG)
L39:L7-L8 (EXP) (ALG)

L40:L36,L37,L38,L39 (EXP) (SIGN MAX)
L41:L36,L37,L38,L40 (EXP) (SIGN MIN)

L42:L40-L41 (EXP) (ALG)



My question is:
As noted above that T1 is the highest temperature. Simply thought we can assume that the biggest expansion stress must come from T1, then why to use load case no 42 (L42: L40-L41 SIGN MAX – SIGN MIN) in order to get the biggest expansion stress?
Do think it would be easier to analyze from the highest temperature (T1) only, then I don’t have to put the rest of temperatures (T2,T3,T4)?
Please enlighten me

Dear Omdo,

T1>T2>T3>T4....>T ambient?
I think those are complete load case set up. L42 performed to have "full expansion stress range" while L40 to have the higer expansioan stress and L41 the minimum expansion stress.

L40, L41, and L 42 are not too neccesary if all T1,T2,T3, and T4>T ambient.

The lowest temperature may cause the higher expansion stress let say if T1=80, T2=60, T3=40, T4=-80, Tambient=19 deg C.

The highest Expansion Stress comes from the maximum expansion stress range, not necessarily from the highest or lowest temperature alone.

Yup, we have no argument on that case, but I'm curious, if we apply the load case no 42, what kind of situation the piping suffer from two cases occur at the same time or extremely, what kind of phenomena would that be, from highest expansion stress suddenly to lowest expansion stress?

How Come?

first of all, I think considering the stress range case is only usefull for tempratures with different signs or if you have an on-off condition for a part of your system and its by pass.
stress range case means a case that your system first gets to the lowest temprature and then gets heated unless it reaches to the highest one. as if your base temprature is your min. temprature and the highest temprature is the operating one while it has been prestressed by the condition of your real base temp. to min. operating temp. so consequently that would be the highest value of your expansion stresses because your system has experienced the largest movement.

Cases 36 - 39 are required, since each could have a different number of associated cycles, so they could each have a different "cyclic reduction factor". Therefore you just can't "look at" the temperatures and decide which case is the worst.

Cases 40 and 41 are "summary" cases, basically reporting the max or min (as specified) from the listed cases. This just saves you from having to individually review cases 36 - 39.

Case 42 doesn't make sense. This will compute a stress range based on the max/min displacements of cases 40 and 41, which don't represent a real situation. Get rid of case 42 - everything else makes sense.