Tank Remaining Life

[Bobfromoh]

I'm not exactly sure what the end product should look like but does anybody have an example of a spread sheet to do remaining life calcualtions for an vessel/tank. I have a history of thickness readings and now I want to make use of the information...or is the spreadsheet a propritary product?

Thanks.

 

[rb1957]

if you know thickness vs time/cycles ...

really all you need is thickness now, which will tell you fatigue life, less current cycles = remaining life

 

[sdz]

Is it a pressure vessel or non pressurized?
Is it a tank?
Do you need a tank design?
What is corrosion rate?

 

[Bobfromoh]

I am presently working with a pressure vessel. I think the general procedure for calculating the remaining life is detailed in the API standards 510 1nd 579? I guess I need to calculate the required thickness and combine this with the available thickness somehow? I thought it might be a "commonly" performed analysis....but maybe not?

 

[kacarrol]

I've used a sheet like that two years ago to work out the remaining life of a piping system. I believe it was API 579 fitness for service. As I recall it was really simple and I think I had decided to re-write it as I didn't like the layout of the one the company gave me.

I don't have my old files with me right now but I'll bring them in Monday and see if I have a copy kicking around somewhere.

 

[Bobfromoh]

That would be great!

 

[kacarrol]

Sorry about the late response, lightning strike knocked out the network here.

I've looked through my files and I didn't save a copy of that spreadsheet.

Good luck!
K

 

[Bobfromoh]

kacarrol,
Thanks for looking!

 

[rb1957]

"I guess I need to calculate the required thickness and combine this with the available thickness somehow? I thought it might be a "commonly" performed analysis....but maybe not?" ...

i don't know your references, but i suspect the calc goes something like wall thickness (decreasing over time) > pressure vessel stress > fatigue life (maybe < endurance limit, GTG) > expired life (number of duty cycles) > remaining life

 

[dcasto]

You calculate the required thickness Tr. You have the initial or last measured thickness Ti. You have the present thickness measured Tp. You have the time period between the Ti and Tp in years, t.

loss or L = Tp - Ti

loss/year or Ly = L/t

remaining thickness R = Tr - Tp

remaining life RL= R/Ly

time to next inspection is the lesser of RL/2 or 10 years

 

[rb1957]

IMHO that's too simple ... as the thickness decreases the hoop stress increases, the fatigue life decreases.

i think you need to start with the original safe life, recalc the safe-life (as the thickness decreases), recalc the remaining life ... not so straight-forward ... maybe a simple way is to use something like miner's rule, summing the damage ratios from various thicknesses. maybe set up the calc from day 1 to the end (sum = 1.0) decreasing the thikcness similar to the measurements ...