Calculating corrosion rates
The corrosion rates are calculated from icorr (the corrosion current) multiplied by the Metal factor. The following formulas are used :
mm/year corrosion rate = (Metal factor X icorr) ÷ 1000
mils / year corrosion rate = (Metal factor X icorr) ÷ 25.4
where Icorr is calculated from:
icorr (A/m² ) = (ba x bc) ÷ (2.3 X Rp X (ba + bc))
ba is anodic Tafel slope in Volts
bc is the cathodic Tafel slope in Volts
Rp is the polarisation resistance in W /m²
The metal factor is calculated from:
Metal factor = (t X K) ÷ r
t (seconds in year) = 365.2422454 * 24 * 60 * 60 = 31556930 seconds
r is the metal density in g/cm²
K the electrochemical equivalent in g / coulombs K is obtained from
K = (atomic % of element X atomic weight of element) ÷ (96487 X Valency of element)
Using the metal editor
The metal editor enables metal factors to be created from known compositions of metals or alloys the properties of the most popular metals and alloys are already included.
Creating a new metal
If a metal is not listed it can be created
the following illustration will create
Brass 70/30. Firstly a new blank metal must be created
this can be done by clicking on
the 
button.
Next the name of the metal is typed and the Accept button is pressed:
This new metal is then transferred onto the main page
in amongst all the existing
metals and is automatically highlighted. The Selected item section will have no
entries. From this point there are two ways of setting the metal factor
the first and
easiest way is to just type the metal factor if it is known into the metal factor box. The
second way is to build the metal up from its elements
and then let the program calculate
the metal factor. Brass 70/30 is composed of 70% Copper and 30% Zinc
to add elements
firstly start with the largest Cu. Click the 
button and the Element selection page will appear:
Move the mouse over to element Cu (29). The Highlighted element section in the bottom left of the page will change to show the element parameters for Cu. Click the left mouse button to transfer all the element parameters to the Element settings section in the bottom right. There are two items which have to be checked first is Weight %. Initially when an element is selected the program calculates the remaining % needed to fill the metal. For the first element the weight % is set to 100 this value should be reduced to 70. The other item which requires attention is the Valency box. The most popular valencies for the selected element are shown in the Valency box. Copper has two typical valencies of 1 and 2. For the example of Brass a Valency of 1 is normally used. If a Valency is not listed then just type the number required into the Valency box. Before Finish is selected the settings for copper should resemble:
Next 30% Zinc has to be added this is done in exactly the same way as for copper the Valency for Zinc is normally 2. The Selected item section on the main page should now resemble:
Finally the metal density for Brass is set to 8550Kg/m>³ and when in the above
example the 
button is pressed
a Metal factor of 2083 is calculated.
Interestingly for selective corrosion such as dezincification the Valency of Cu should be set to 0.
The program is able to automatically suggest a density if there is only one element which is set to 100% composition.
Editing an existing metal
Existing metals can be edited by first choosing the metal. The element to be edited is selected and the Edit button clicked. On the Element page the settings can then be changed remember to re-click the Calculate button to get the new metal factor.