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Creep and Fatigue stress from power plan components

  1. Jan 17, 2008 #1
    Hi, I'm new here, and I'm not really sure where this thread goes, so please feel free to move it

    1. The problem statement, all variables and given/known data
    basically, I'm doing a project involving converting raw data on pressure and temperature (and time) in a power plant situation (mainly the pipes carrying the steam)

    here is a document which outlines some of the things I'm looking at:
    http://www.structint.com/tekbrefs/CFPRO3_2002.pdf

    at the top of page three is the basic process i would like to carry out for my project (initially just the top part leading to the total damage graph)

    however, i am not the most learned fellow in this field and am coming here to seek some help from someone who is. basically, i would like to know if anyone knows of any places which will help me understand the basics first then the specific steps involved in getting at least the creep rupture curve and S-N curve, but any help would be greatly appreciated.

    I can currently convert the pressure to the creep stress and i understand that i will need to use finite elements and green's function to get the fatigue stress (am i right here?)

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jan 19, 2008 #2

    Tom Mattson

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    This looks more like a research problem to me. I'm going to send it over to the Engineering department for discussion.
     
  4. Jan 20, 2008 #3
    I was able to find the equations in this pdf (http://www.materialsscience.pwr.wroc.pl/ap/articles/ms_2007_036.pdf), which was a great help

    however, now all i need are the constants

    since i am not finding them through experimentation and i plan to do it over a few different metals does anyone know a good 'database' of these constants relating to the different metals involved?

    Thanks
    Sam
     
  5. Jan 21, 2008 #4
    nah, its more like the maths behind it that is important, thanks all the same though

    probably for the moment i only need the material constants for one type of material (just so i can get the calculations up and running, i have got some constants (for fatigue calculations) for Steel 4340 but still haven't got a complete set for creep etc.)

    i don't really mind what material it is at the moment, i have decided to try and get the maths working (in python) first.

    Thanks for the help :D
     
  6. Jan 21, 2008 #5
    Also, i'm wondering if anyone knows any good Finite Element Analysis Software (preferably for windows, but linux could be ok) that would be able to find the fatigue stress as a result of the cyclic heat on the steam pipes? even if i just make up reasonable constants atm this is the only mathematical barrier i need to get around.

    i tried code aster (pachted for windows) but it failed to install properly, but i would consider trying it in linux if anyone recommends it for what i need
     
  7. Jan 22, 2008 #6
    ok, so i've been using some dummy constants in the creep damage calculations and i'm able to calculate creep YAY

    so, the next step (besides getting real constants) is to make it automated off a 'data collecting system'

    my two inputs from this are collected every ten minutes, pressure and temperature, so, i don't really have enough knowledge about creep to be sure so hopefully someone here does,
    but i was hoping that finding the total creep damage would be a matter of adding each small damage calculation up (small damage calculation = ten minutes / expected rupture time from the data for that 10 minutes) (considering for some ten minute blocks there will be no pressure (during powerplant shut downs) and it will be changing)

    the raw data is taken at the end of each 10minutes, so I will probably average the start and end pressures/temperatures for each ten minute block.

    i hope i am making sense here, if you know a bit about what im talking about but can't properly understand me, just ask for some clarification :D

    Thanks
    Sam
     
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