Corrosion Rate

[RBMECH123]

Hello All,
I am conduction a vessel analysis in which I am no sure on something. Is there a formula/equation for the rate of corrosion (per year). My study is regarding a 53 year old tank in which I am trying to estimate a life expectancy before the material corrodes to the minimum required cylinder thickness. Thanks in advance!
-Richard

 

[metengr]

RBMECH123;
If you have information as to the original wall thickness of the vessel and measure the current thickness you can use information to establish a linear corrosion rate for in-service conditions assuming constant conditions.

If you are asking what is the corrosion rate of a particular metal in a certain environment, this would require access to a corrosion handbook that lists material corrosion rate (mils/year) as a function of service temperature and environment.

Third, if you have access to API 579, this can guide you.

 

[DVWE]

API 510 is also an excellent document. It has a few different calcs:

Short Term CR: previous thickness (prior inspection t) minus actual thickness (most recent thickness measurement) divided by time (years) between t previous and t actual.

Long Term CR: initial thickness (newly built vessel t) minus actual thickness divided by time (years) between t initial and t actual.

Remaining Life: t actual minus t required divided by corrosion rate.

 

[RBMECH123]

metengr,
I have the original nominal thickness, the current thickness readings (N,W,E,S, using lowest amount), and the age of the vessel. I basically used an equation, dividing the difference of thicknesses to the amount of years its been in service. Is this be correct?

 

[RBMECH123]

DVWE, beat me to it, great, I just had to make sure there wasnt any specific code equation. Thanks you two!

 

[rmw]

And.... I think metengr and DVWE's answers assume that the service for the tank wasn't changed. If you are using the tank for something else than it was used for for 53 years, that is a different matter.

Wow, 53 years and still in service. I wish I had held up that well.

rmw