Hi all,

I need to perform a stress analysis of a fired heater that operates cyclically with the following cycle:





Other informations available:

-Piping Temperature distribution for each moment of the cycle;
-Min Ambient temperature/Ambient temperature: -43°C/25°C;
-Design temperature;
-Design and operating pressure;
-Operating cycles: 15000;
-No pressure fluctuations are foreseen.

After finalazing the model I've set the following load cases:

L1 WW+HP HYD
L2 W+T1+P1 OPE
L3 W+T2+P2 OPE
L4 W+P1 SUS
L5 W+P2 SUS
L6 L2-L4 EXP
L7 L3-L5 EXP

where T1,P1 design temperature and pressure, T2,P2 temperature and pressure in a specific moment of the cycle (operating).

My question is:
Wich kind of load cases for fatigue should I set for this cycle?

I hope it's clear.

TY.

If I was running a B31.3 analysis, those EXP cases are set for fatigue evaluation. Turn that 15,000 cycles into f in the allowable stress range (SA) calculation.
[If T1 is above ambient and T2 is below ambient, then I might run L8: L2-L3 (EXP).]

You say that I dont'need to follow rules from BPV Code, Section VIII, Division 2 or Division 3 as specified in paragraph K304.8 Fatigue Analysis on AME B31.3?

My first solution was import in Caesar model the fatigue curve (5-110-1A.FAT, piping material is A333 grade 6) and in the load case editor set those expansion cases as FAT (with 15000 cycles).

Am I completly wrong?

I was unaware of your high pressure classification.
High pressure gives thick wall. Thick wall may also present issues with through the wall stress and fatigue that are not part of CAESAR II.
I would not say that CAESAR II fatigue analysis satisfies the requirements contained in VIII-2 or VIII-3.