Code 2843 (ASME BPVC.CC.BPV.S4), transient problem

[WRH_36]

Hello, I performed a thermal and stress analysis in a cooling process and attempted to comply to the code case 2843 (temperature is high). The initial temperature is 650C. It is a transient analysis with 10 time sets from 60s to 600s. I have obtained the thermal stresses at each time set. To treat the transient problem following the code 2843, using "delta_Q = | max(Q_i) - min(Q_i) |, where Q_i indicates stress values at the timepoints." I defined several spots on objective part to evaluate the thermal stress at different time set. For example, to determine delta_Q at 120s, the membrane stress is constant at a spot, and I can obtain the bending max and min at 120s, to determine delta_Q. I am not sure if it is a right approach.
If anyone has experience in this field, I would appreciate guidance on how to apply Code Case 2843 to address transient problems.
Thanks,

WRH

 

[TGS4]

This Code Case is for creep. I highly doubt that you will anything but negligible creep in under 10 minutes. What is your actual time-at-temperature?

 

[WRH_36]

Thank you for your response. Yes, Code 2843 is for evaluating creep-fatigue damage in pressure vessels and other components operating under high temperatures.
The part in question is a freeze valve that operates at 650°C with a service life of one year and undergoes 300 cooling processes. The valve is cooled by air at 20°C to freeze the liquid inside, which has a freeze temperature around 460°C. The test results show that the lowest temperature on the valve could be around 420C depending on the cooling air flow rates.
Currently, I am conducting a stress assessment rather than evaluating creep-fatigue. I performed a transient structural analysis using ANSYS by importing the transient body temperatures of the valve and obtained the linearized stresses (membrane and bending stress) at the points of interest.
I followed the criteria specified in Code 2843. However, regarding the thermal stress caused by the cooling process, I have not previously conducted an assessment for the transient state.
Here is what I did to assess the thermal stress for this transient analysis. To determine delta_Q (delta_Q = |max(Qi)-min(Qi)|, where Qi indicates the stress value at the timepoints), I determined the maximum and minimum membrane and bending stressed throughout all time sets (total of 10 time sets - 60s, 120s, ...600s). delta_membrane = max (membrane)-min (membrane), delta_bending = max(bending) - min (bending). delta_Q = delta_membrane + delta_bending.
I followed the criteria specified in Code 2843. However, I am uncertain if my approach to the transient state is valid. For the steady state, the stress assessment aims to determine the resultant stress at the points of interest.
Your guidance on the validity of this approach and any suggestions for improvement would be greatly appreciated.
WRH

 

[TGS4]

I'm going to recommend that you hire an expert in creep design to assist you with this. I have some creep experts in my company (I am not one of them) that I would go to if I were in your situation. Unfortunately, I would not be able to provide competent guidance on the validity of your approach.