Hello,
I am currently studying corrosion on alloys and I have found this formula which calculates corrosion rate (CR) from the mass loss (Δm/t) and the density of the alloy (ρ):
CR (µm/yr) = 87600*Δm/(ρ*t)
Can anyone please explain to me the reasoning behind the constant 87600? Or the original paper on how was it derived? I agree the mass loss comes directly from experiments, but I think this formula it's quite simplistic (I mean experiments are usually performed during the spam of hours - days maximum, which should be difficult to extrapolate in term of years). On the other hand, I do not agree this parameter should not be a constant (it should depend upon on the experimental setup, temperature, etc.).
I tried to check the book ''Principles and prevention of corrosion" by Jones but no explanation on this topic.
Thank you very much for your time and consideration!
Dear Dr. Rafael Herschberg ,
the costant 87.6 (87600) is used convert the corrosion rate between the mils per year (MPY) and the metric equivalent millimeter per year (MM/Y or µm/Y), you can use the following equation to convert mils per year to micrometers per year (MicroM/Y):
MM / Y = 87.6 x (W / DAT)
where:
W = weight loss in milligrams
D = metal density in g /cm3
A = area of the sample in cm2
T = time of exposure of the metal sample in hours
For more details, please see the source: Converting Corrosion Rates by ThoughtCo, available at: https://www.thoughtco.com/corrosion-rate-calculator-2339697
My best regards, Pierluigi Traverso.
The constant 87600 in the corrosion rate formula represents the number of hours in a year (24 hours/day x 365 days/year = 8760 hours/year). This conversion factor is used to convert the mass loss rate (in units of g/hour) to a corrosion rate (in units of µm/year). The formula assumes that the mass loss rate is constant over time, and the mass loss during the experimental period can be extrapolated to a longer period (e.g., one year) using the conversion factor.
The formula is a simplified approach for estimating the corrosion rate of metals and alloys in different environments. It is based on the assumption that the corrosion process is linear over time and the mass loss can be attributed solely to corrosion. In reality, corrosion rates can vary over time and may depend on a variety of factors such as the environment, temperature, pH, and alloy composition.
The corrosion rate formula has been used in corrosion research and engineering for decades and is based on empirical observations of corrosion behavior. The derivation of the formula is not attributed to a specific paper or study but rather to the general practice in corrosion science and engineering.
It is important to note that the corrosion rate formula is a simplified approach and should be used with caution, especially for materials with complex corrosion behavior. For accurate and reliable corrosion rate measurements, more sophisticated methods such as electrochemical techniques or weight loss measurements under controlled conditions may be necessary.
I agree with john
8760 is the hour number by year. weight loss is given in mg /cm2 , to con vert is in g/cm2 , 10-3 is involved. so the constant is 8.760 to express the corrosion rate in cm/y . or 87.6 to be mm/y.
Truth be told, a dimensionless and non-validated constant such as 87600 is needless in the model for corrosion rate determination ..., the model "CR=dm/Apt" still functions perfectly even when correlated with experimental data. I strongly disagree to the 87600 as applied to the model
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