COMPUTER APPLICATION IN PIPELEINE CATHODIC PROTECTION DESIGN

Sami MasadehMaterials Engineering Department

AL-BALQA APPLIED UNIVERSIYJORDAN

Abstract

Cathodic protection is one of the most effective techniques of corrosion prevention for pipe metals combined with special kinds of coating, because in some situations, it could completely stop corrosion, in the other hand, it lasts for a long time, and relatively costs less than other prevention techniques.

Cathodic protection is perhaps the most important of all approaches to corrosion prevention. By means of an externally applied electric current, corrosion is reduced virtually to zero, and a metal surface can be maintained in a corrosive environment without deterioration for an indefinite time. More details will be discussed in the next chapter.Both anodic and cathodic protections utilize electrochemical polarization to reduce corrosion rates. Otherwise, mechanisms are different, as well as the methods and equipment for implementation. Anodic current uses an anodic current to polarize the corroding surface into a potential region where passivity is stable. Cathodic protection uses a cathodic current to polarize the surface to more active potential that suppress the anodic dissolution rate. Anodic protection is effective only for active-passive metals or alloys that form a resistant passive film. Cathodic protection can be effective for any metal or alloy. The throwing power, or ability to be transferred over distance, is high for anodic protection because very low current are applied, usually in low resistivity electrolyte. Throwing power is much lower for cathodic protection because higher currents are required, often in solution of much higher resistivity.

In this work, a cathodic protection program was made to ease the cathodic protection design.

Keywords: cathodic protection, pipeline, attenuation constant, soil resistivity

INTRODUCTIONRegardless of the type of cathodic protection system to be installed, principle measurements should be conducted prior to beginning the system design; these measurements are voltage, current and resistivity. The voltages and currents directly involved with the protection circuits are unidirectional. Alternating current and voltage measurements for rectifier input circuits are made in the same way as A.C. power measurements. Whenever possible, a trial and error process using a temporary ground bed

and a portable power supply should be used to determine the current required to protect the structure.CATHODIC PROTECTION DESIGN PROCEDURE

Designs for impressed-current have some common steps, which are listed, as follows:

1. Area to be protected. The calculation of exposed surface areas is not given necessary care. Areas may easily be underestimated in complex structures subject to a variety of environments, and the cathodic protection system subsequently underdesigned.

2. Polarized potential. The primary criteria in use of cathodic protection involve the appropriate polarized potential. The current density needed to achieve this potential is used in the design of the system.

3. Current demand. Required current is calculated simply from the product of area and the corresponding current density requirement. Many structures have areas exposed to a number of environments; Separate calculations are required for each environment.

The amount of current required for complete cathodic protection can be determined by one of the following three ways:

An actual test on existing structures using a temporary cathodic protection setup.

A theoretical calculation based on coating efficiency. An estimate of current requirements using tables based on field

experience. Approximate cathodic protection current requirements based on coating quality are given in table 1.

Table 1:Typical current density requirements for cathodic protection of steel.(1)

Coating quality Coating resistance (ohm.m)

Protection current (mA/m2)

Very weak 100 - 200 1.0 – 2.0Weak 200 – 500 0.5 – 1.0Medium 500 – 1000 0.1 – 0.5Good 1000 – 2000 0.05 – 0.1Very good 2000 – 10000 0.01 – 0.05Excellent More than 10000 Less than 0.01

4. Soil Resistivity. Soil resistivity should be determined for the specific area where the groundbed is to be installed. Even small differences in location can cause

large differences in soil resistivity. Soil resistivity may be determined by using Wenner (4-pin) procedure.

5. Anode consumption. Total required weight of anodes is determined from known consumption rates for the calculated current demand. For impressed current anodes, consumption is optimized to yield minimum cost for current provided from an external supply.

6. Anode number and distribution. The weight of anode material consumed must be divided into an appropriate number of anodes, which are distributed around the structure to give as close to uniform current distribution as possible. The choice of anode distribution is more art than science, and experience plays a major role because potential and current distributions in the electrolyte can only be approximated, even for the simplest system geometries.

7. Design output current. From the anode resistance, R, and driving voltage, E, of the selected anodes, the design output current can be calculated from ohm's law, E=IR. In a proper design the output current will at least match or exceed the required current calculated. Cathode resistance is usually assumed negligible, compared to anode resistance and neglected in the calculations.

The Program

Figures1 &2: The main screen and main menu of the program.The main page represents the application's navigation menu, as shown in Figures 1&2, the user can easily navigate through five choices which are:

1. The Introduction section: This offers a brief overview about corrosion and methods of protection including ICCP.

2. The Calculations section: This section allows users to perform ICCP calculations.

3. The Terms and Tables section: This links users to a useful list definitions and tables.

4. The Prepared by Section: shows the project team.

5. Exit: This link allows users to quit the application.

INTRODUCTION.

When user clicks the introduction link, figure 3 will show up.

Figure 3: The content page in the introduction section.

The introduction screen contains three main categories which are:

1. Corrosion: this links the users to another screen, which contains further subcategories for corrosion, as following :

- Corrosion definition.- Economic losses of corrosion.- Theory of corrosion.

2. Protection of metals: links the users to a screen, which contains protection techniques, as following:

- Material selection.- Design.- Coatings.- Anodic protection.- Cathodic protection.

3. Cathodic protection: links the users to a screen, which contains the type of

cathodic protection which are:

- SCP (Sacrificial Cathodic Protection).- ICCP (Impressed Current Cathodic Protection).

4.2. CALCULATIONS

The calculation screen shown in figure 4 is divided into four logical sections as follows:

A. The inputs section: This contains the controls that allow users to efficiently supply their input values to the application.

B. The outputs section: This contains the non-editable display controls for showing calculation results acquired depending on user inputs.

C. The Commands panel: This contains a several clickable controls, each performing a desired functionality.

D. The application standard menu: This menu allows users to manage the application in a standard way. It contains all of control and calculations abilities.

4.2.1 THE INPUTS SECTION.

Figure 5 represents a snapshot of section (A) (the inputs). The user may provide the inputs either by entering the value directly into the text boxes (as in 4 and 5 text boxes), or by using the pull-down menus (as in 1, 2, 3 and 6 menus) that automatically fills the corresponding values into their actual places. When using pull-down menus special actions occur as follows:In pull-down menu (1), a list of possible pipe's diameter in inches appears and selecting a value will automatically result to fill the value in meters. As shown in figure 6.

In pull-down menu (2), a list of possible pipe's lengths in kilometers appears and selecting a value will automatically result to fill the value in meters. As shown in figure 7.

In pull-down menu (3), a list of possible coating quality estimations appears and selecting a value will automatically result to fill the coating resistivity and protection current density. As shown in figure 8.

In pull-down menu (5) the user can choose the anode type and the application will automatically fill the anode consumption rate depending on the selected value.See figure 9.

C

Figure 4: The calculation page divided into four section. When the user clicks on the "have data" button, a small form shows up as shown in

figure 10. This form provides a simple way to calculate the soil resistivity when not known for the user by providing other user-known values.

The form takes three values as an input (1). When user clicks on (2), the calculated result will appear in (3).

When user clicks on (4) "submit" the resulting value will be copied back to the main calculation form filling the soil resistivity value.

Figure 11, shows pull-down menu (6) which provide a way to select the system life in years.

4.2.2. THE OUTPUT SECTION.

Figure 12 shows the section (B) of the calculation form, which will show the resulting output of the given inputs.

Figure 5: Snapshot of section A of the calculation page (the inputs).

Figures 6&7: Pull-down menu of the pipe's diameter (inch) and length (km)

Figures 8&9: Pull-down menu of possible coating quality and anode type.

7

2

3

1

5

4

6

Figure 10: Pull-down menu of system life (years).

Figure 11: 4-wenner technique's to calculate soil resistivity page.

Figure 12: Section (B) of the calculation form (the output section).

The outputs consist of six values:- Number of anodes.- Distance between anodes.- Weight for each anode.- Total current required for protection.- IR drop.- Distance between anode and pipe.

1

1

423

Figure 13: Section (C) of the calculation page (command panel).

Figure 13 shows the command panel section of the calculation form. As it shows:

- The Calculate command button: when the user presses this button, the Program does all the required calculations, and put the results in the output text boxes. If the user doesn’t fill one of the required inputs, the program doesn’t do the required calculations, and alerts the user to fill these missing inputs, as shown in figure (14).

- The Clear All command button: when the user presses this button, all of the input and outputs text boxes are cleared, so the user can re-enter data and calculate them.

- The Main Page button: when pressed it links back the user to the main page.

- The Exit button: when the user presses on this button it quits the program, and a message box appears to confirm if the user wants to quit.

Figure 14: Message box appears and one input turns red to alert the user.

4.2.3. STANDARD MENU

1 2 34

The menu bar consists of three menus, as follows:

1. The File menu: shown in figure 14, contains four menu items which are: Save, Load, Main Page, and Exit.

Figures 15&16: File menu in the menu bar and calculations menu in the menu bar.

Figures 17&18: Help menu in the menu bar and Save as dialog box.

2. The Calculations menu: shown in figure 16, contains three menu items which are: Soil resistivity, C.P Calculations, and Clear All.

3. The Help menu: shown in figure 17, contain two menu items which are: Terms and Tables, and About.

4.2.3.1. FILE MENU

When the user opens the file menu, three items can be found. When the user wants to save his data, he presses on the Save item in the file menu (or use Control + S shortcut) and a dialog box appears (as shown in figure (18)); to allow the user to choose where to save his file (which has an *.iccp extension).After specifying the location and name of the file, the user must

press on the save button to save or can press on the cancel button to cancel the saving process.

Figure 19 &20: A file saved by the user, opened by notepad and Open dialog box.

After saving the file, the user can open the file to preview the saved information, which are saved as the following format shown in figure 19.The user can print his data as a report containing date, time, inputs, and outputs as the following sample report:

If the user wants to load a previously saved data, he must press on the load item in the file menu (or use Control + L shortcut), an open dialog box will appear (as shown in figure (20)) to allow the user to specify the location and name of the desired file, then he has to press on the open button to load the data or press the cancel button to cancel the loading (opening) process.After loading the data from the file, the calculation form will be filled with the corresponding values of inputs and outputs as in figure (21).

Figure 21: Filled calculation page by the loaded data.

The user can also return back to the main menu, by pressing on the Main Page item in the file menu (or use Control + M shortcut).

The user can also exit the program by pressing on the Exit item in the file menu (or F4 shortcut); a message box will appear to confirm the quitting.

4.2.3.2. CALCULATIONS MENUWhen the user presses on the Calculation menu, three items will appear as in figure (16). If the user presses on the Soil resistivity item in the calculation menu (or F2 shortcut), a Form as in figure (11) will appear.

If the user presses on the C.P Calculation item in the calculation menu (or F3 shortcut), the program will perform the calculation that include the inputs and result with the output.

If the user presses on the Clear All item in the calculation menu (or Shift + Delete shortcut), all the input and output texts will be cleared.

4.2.3.3. HELP MENUIn the help menu the user can get some information from existing definitions, and tables, or can get information about the program, or system information.

If the user presses on the Terms and Tables item in the help menu (or uses F1 shortcut), it will make a link to the terms and table page; where the user can make use of the existing terms and tables.

If the user presses on the About item in the help menu (or uses F9 shortcut), an information form will. Containing the description of the program, and showing the program's icon. If the user presses on System info button, a form containing information about the user's computer will appear.

REFERENCES1- John H. Morgan, Cathodic Protection, 1st Ed, Leonard Hill [Books] Limited,

London, p. 51, 19592- Stephen P. Turnipseed, ‘Cathodic Protection in Oilfield Brine’, Materials

Performance, Vol. 30, No.12, p. 16-20. 1991.3- H. Yalcin & T. Koc, Katodik Koruma, 1st Ed, Palme Pub. p. 72.4- Rodney J. Dice, ‘Maximizing the Lifetime of an Impressed Current Cathodic

Protection System’, Materials Performance, Vol. 32, No.6, p. 27-29. 1993.