Modeling & Simulation for West Qurna (Tuba-1) Cathodic Protection Design by using MATLAB Simulink

This study focused on the two systems of Cathodic Protection, CP, (temporary (Sacrificial Anodes, SACP) & permanent (Impressed Current, ICCP) that were used to protect West Qurna (Tuba-1) crude oil pipeline42 in / Basrah Oil Company, BOC, from corrosion challenges. Design Calculations for CP systems were achieved according to the standards of National Association of Corrosion Engineers, NACE. These calculations were simulated using Matlab –Simulink Software 2018. Then, the simulated design was converted to Graphical User Interface, GUI. This GUI allows the user to enter the design data & perform the calculation faster & more efficiently. Furthermore, GUI was converted into a dependent program by installing Matlab Runtime Installer which enables the execution of Matlab files on computer without installed version of Matlab. The results showed that there was matching between the calculations of CP design & the simulated design. SACP demonstrated that 4 Mg anodes are required to protect 1 km of sec.1 of pipeline for 4 years period while 6 Mg anodes are required to protect 1 km of sec.2 for 11 years period. ICCP system for sec.1 of pipeline requires 4 magnetite anodes to supply 2.86 v by rectifier in accordance with horizontal bed resistance RH ≤ 1.5 Ω while sec.2 requires 25 magnetite anodes to supply 2.45 v by rectifier in accordance with vertical bed resistance Rv ≤ 1.5 Ω. The designed program proved that it was easy to install & efficient in making Calculations. According to the above, this program can be adopted in prediction studies to know the design outputs (No. of anodes, required current for protection & voltage supplied by rectifier).


Introduction
Cathodic protection (CP) is an electrochemical technique used to reduce corrosion damage to active metal surfaces by reducing the potential difference between the anode and the cathode.
It is used around the world to protect pipelines, water treatment plants, submarine and water storage tanks, ships and hulls, offshore production platforms, concrete structures and steel bars in docks, etc. [1] [2] . Pipes are used to transport fluids (liquids and gas), such as water, crude oil, and natural gas. In petroleum industry, they are used to transport oil from the production area to the export loading and unloading dock, or to processing units like oil refineries. Most of them made of carbon steel and built underground (subsoil of various types (dry and wet) and layers). Almost any water-containing environment can promote corrosion that occurs under many complex conditions in oil and gas production, processing, and piping systems [3] [4]. The heterogeneity of soil components leads to potential difference which are considered the main cause of corrosion cell development on the pipeline surface. Soil resistivity is considered a significant determinant for soil corrosivity [4]. CP with coating or paint are considered to be the best suggested solution to minimize corrosion challenges for buried pipelines. CP techniques are classified into two types, sacrificial anodes & Impressed currents. The 1st type is used for temporary protection (for short periods) for above water steel storage tanks & underground steel pipeline (during impressed current installation) while impressed current used for permanent protection (long period) for underground and subsea steel structures [5,6]. Simulation modeling solves real world problems safely efficiently. It provides an important method of analysis which is easily verified, communicated and understood. Matlab software is considered the most common important program has a lot of applications in the lab and field. One of its applications is Simulink. It is utilized to simulate any process in different fields in an efficient and easy way [7,8].
The aim of this study is to simulate the Cathodic protection design for West Qurna pipeline 42 in using Matlab Simulink 2018 and turn this simulation into dependent program achieves the design calculations of CP system efficiently.

West Qurna Pipeline (1-Tuba)
The West Qurna pipeline 42 in (1.067 m) diameter with length of 70.5 Km is divided into two sections, the first section 46 km while the second 24.5 km. of the West Qurna pipeline which were provided by BOC. Figure (1) shows the roots of the West Qurna pipeline.

Equation Parameters
Pipeline

Simulation
The CP design for West Qurna pipeline was simulated using Matlab -Simulink 2018. Figure   (2) depicts the steps of the simulation in Matlab software.

CP Design Outcomes
For sections of West Qurna pipeline, Table (7) represents the values obtained from the sacrificial anodes -design equations.

Simulation Outcomes
The simulation results for sacrificial anodes CP system for West Qurna pipeline sections are illustrated in Figures (3-A), (3-B) respectively. The simulation results for impressed current CP system for West Qurna pipeline sections are depicted in Figures (4-A) , (4-B) respectively.

Fig. (4-A)
Simulation results for Impress Current CP system for West Qurna pipeline sec. 1. Fig. (4-B): Simulation results for Impress Current CP system for West Qurna pipeline sec. 2.

Sacrificial anodes simulation
According to the findings, 4 Mg anodes per 1 Km of pipeline-sec.1 with a 4 year design life are required for CP system. While for sec.2. 11 Mg anodes per 1 Km of pipeline with 6 year' design life is required for CP system.

ICCP Simulation Discussion
For sec.1, the results revealed there are 4 Magnetite anodes that satisfy the horizontal ground bed resistance criteria (R H <= 1.5 ohm) and the CP circuits power supply voltage is 2.86 V.
While for sec.2, the results revealed that there are 25 Magnetite anodes that satisfy the vertical ground bed resistance criteria (R V <= 1.5 ohm) and the CP circuits power supply voltage is 2.45 V.
According to the above, it was noted that there was matching between design calculation results (that were explained in Tables 7 & 8

Sacrificial anodes GUI
Sacrificial anodes simulation model is turned into GUI using Matlab. The executed designed GUI for sacrificial anodes CP system is depicted in Figure (

Voltage Cone Plot
Voltage cone [10]will happen due to pass a current from anode through soil (I.e. voltage drop from point to another in electrolyte) this gradient result in voltage rise in pipe to soil potential.
Voltage rise can be calculated through (1).
Where U r , voltage rise, I, anode current, L, anode length, r, radial distance from anode as shown in Figure (6). Then total rise voltage, E T , is calculated through (2): In the above figure, voltage rise is calculated at r= 400 m from anode, and then divided the result on total rise voltage as shown in (3), the obtained ratio is 0.043 % < 5% [12] (for each sec. of pipeline) which is considered acceptable ratio.

Impressed current simulation
The executed designed GUI for Impressed current CP system is depicted in Figure (  c-Utilizing impressed current CP system for sec.1 of pipeline requires 4 magnetite anodes to supply 2.86 v by rectifier in accordance with bed resistance R H ≤ 1.5 Ω.
d-Utilizing impressed current CP system for sec.2 of pipeline requires 25 magnetite anodes to supply 2.45 v by rectifier in accordance with bed resistance R v ≤ 1.5 Ω.
 The GUI model for each type of CP system proved its efficiency to calculate the required design outputs for protection.
 Installation and dealing with the designed program in a way that ensures accurate and quick calculations is simple.