There are many methods for evaluating the corrosion rate of metals, but the main methods are as follows:
1. Corrosion quality assessment method
The speed of metal corrosion can be evaluated by the amount of metal loss per unit time and unit area:
in:
K w = corrosion rate, unit g/(m 2 h)
W 0 = the mass of the metal test piece before corrosion, unit g;
W 1 = the mass of the metal test piece after corrosion (after removing the corrosion products) , g;
S=the surface area of the test piece in contact with the corrosive medium, m 2 ;
t=corrosion time, h.
2. Evaluation method of corrosion depth
The corrosion rate of metal can also be evaluated by the depth of metal corrosion per unit time, and the relationship between it and Kw of the quality evaluation method is:
Among them, K is the corrosion rate represented by the corrosion depth, mm/a; d is the density of the metal, g/cm 3 ;
When the above-mentioned corrosion quality evaluation method and corrosion depth evaluation method are used to evaluate the metal corrosion rate, it can only be used as a reference in the case of uniform corrosion. For localized corrosion, other corrosion rate evaluation methods should be used for evaluation.
3. Evaluation method of mechanical properties change
We know that corrosion will lead to a decline in the mechanical properties of metals, so we can test the mechanical properties of metals before and after corrosion, and evaluate the corrosion rate of metals by the changes in their mechanical properties.
This method is suitable for both uniform corrosion and localized corrosion. The evaluation is usually expressed by the change of strength limit or the change of elongation:
Kσ: rate of intensity change, %;
Kδ: corrosion rate of elongation change, %;
σ: the strength limit of the metal before the retest, Mpa;
σ': strength limit of metal after corrosion, Mpa;
δ: metal elongation before retest, %;
δ': elongation of metal after corrosion, %.
