Before starting a corrosion calculation, user needs to specify parameters of the corrosion process as the data input. Data input and validation functionality is provided by the FREECORP user interface. User should enter data into corresponding textboxes as shown in figure (click on the image to see it enlarged) or click Default Data button to reset the model to default values.



Corrosion model parameters are given in Table 1 with corresponding default values. The user should enter any parameter value for his/her model into corresponding textboxes. The user also can modify units for all numeric parameters. For list of available units see unit conversion tutorial. Step-by-step instructions for entering data are given in the tutorial.

Table 1

Parameters			Reactions
Name	Default Value	Unit	Anodic	Cathodic
Temperature	20	C	Iron_dissolution	H+_reduction
Pressure	10	bar		H2O_reduction
Diameter	0.1	m		H2CO3_reduction
Velocity	1	m/s
CO2	0	bar
H2S	0	ppm(g)
Fe++	1	ppm(w)
HAc	0	ppm(w)
pH	4
O2	0	ppb(w)
TimeMax	0	Hour

For fluid velocity user may enter diameter and velocity values for the corrosion prediction in pipe systems, or diameter and number of revolutions (rpm) for rotating cylinder (in the latter case FREECORP calculates fluid velocity).

If at any time user wants to reset model to default values, button Default Data can be clicked to perform this action. According to default data input CO₂ is a dominant corrosion mechanism. In the default model the electrochemical reactions included in the model are as above corresponding to default values.

As user enters data, the status bar at the bottom of the program window reports important messages. As parameter values are typed into the model their values are validated by the program. There are three states regarding validity of data: correct, warning, and incorrect.

1. When all the data is correct, correct state signifies that model can be executed, and in that state Calculate Corrosion Rate button is enabled.
2. Warning state signifies that model can be run, but parameter values and calculation are outside of the model calibration range. In this state, parameters which have the values outside of the calibration range are shown in red, but Calculate Corrosion Rate button is enabled. In this case user interpretation of program calculation in relation to experimental data should be taken with great caution.
3. Incorrect state signifies that some data are incorrect, the incorrect values are shown in red, status bar displays context sensitive message and the Calculate Corrosion Rate button disabled.

In addition users should be aware of some other considerations as follows:

1. Calculate Corrosion Rate button will be disabled as long as incorrect data exists.
2. Status bar only shows information for one specific data input at a time. To get more information, users can move mouse to the corresponding textbox with the values shown in red.

When user enters data into textboxes, the validation of data input is processed instantaneously. Four main data errors or limits are checked:
1. Non-numeric characters. Alphabetic character cannot be typed into textboxes from keyboard. Only characters ‘1-9’ and ‘.’ are allowed. Textbox keeps focus until error is corrected. Data status is set to be incorrect.
2. Invalid numeric data with allowed characters, for example, ’32.1.32’, ‘.4.3.’, or ‘ ‘ blank. Data status is set to be incorrect, data are shown in red, and values have to be corrected to allow the calculation.
3. Soft limit. Each data input has a specified range of recommended values. If data input is out of this range, data status is set to be warning, corresponding warning message is shown in the status bar. Calculation can proceed.
4. Hard limit. Each data input has a specified range of allowed values. If data input is out of this range, data status is set to be incorrect, corresponding error message is shown in the status bar. Calculation cannot proceed. Soft and hard limits for individual parameters are shown in Table 2.
5. Additional restrictions. The sum of partial pressure of H2S and CO2 cannot exceed total pressure. Concentration of H₂S and O₂ are mutually exclusive. Time of simulation tmax is valid and enabled only for H₂S corrosion i.e. when concentration of H₂S is greater than 0 (zero).

Table 2

Parameter Name	Low Bound of Soft Limit	Up Bound of Soft Limit	Low Bound of Hard Limit	Up Bound of Hard Limit	Unit
Temperature	1	120	0	200	C
Total Pressure	1	300,000	0	300,000	bar
Diameter	0.01	1	0.0000001	10,000,000	m
Velocity	0.001	20	0.0000001	10,000,000	m/s
CO2	0	*	0	*	bar
H2S	0	*	0	*	ppm(g)
Fe++	0	100	0	10,000,000	ppm(w)
Undissociated HAc	0	10,000	0	10,000,000	ppm(w)
pH	3	7	1	14
O2	0	10,000	0	10,000,000	ppb(w)
TimeMax	0.0001	None	0.0001	None	Hour

* The sum of partial pressure of H₂S and CO₂ cannot exceed Pressure.