BORANG PENGESAHAN STATUS TESIS

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1 JUDUL: Saya PSZ 19:16 (PIND. 1/97) UNIVERSITI TEKNOLOGI MALAYSIA BORANG PENGESAHAN STATUS TESIS DESIGN OF CATHODIC PROTECTION FOR SUBMARINE PIPELINE SESI PENGAJIAN: 2006 / 2007 WAN NORSHUHADA WAN KHAIRUDDIN (HURUF BESAR) mengaku membenarkan tesis (PSM/ Sarjana/ Doktor Falsafah)* ini disimpan di Perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut: 1. Tesis adalah hakmilik Universiti Teknologi Malaysia. 2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. 4. **Sila tandakan ( ) SULIT TERHAD (Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972) (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/ badan di mana penyelidikan dijalankan) TIDAK TERHAD Disahkan oleh (TANDATANGAN PENULIS) (TANDATANGAN PENYELIA) Alamat Tetap: KG. SERDANG MUDA PROF. MADYA DR. NORDIN MELOR, YAHAYA KOTA BHARU, KELANTAN Nama Penyelia Tarikh: 23 APRIL 2007 Tarikh: 23 APRIL 2007 CATATAN: * Potong yang tidak berkenaan. ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/ organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.

2 iv Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek Sarjana Muda (PSM).

3 I hereby declare that I have read this project report and in my opinion this project report is sufficient in terms of scope and quality for the award of degree of Bachelor of Civil Engineering. Signature :... Supervisor : Prof. Madya Dr. Nordin Yahaya Date : 23 April, 2007

4 4 DESIGN OF CATHODIC PROTECTION FOR SUBMARINE PIPELINE WAN NORSHUHADA BINTI WAN KHAIRUDDIN A report submitted in partial fulfillment of the requirement for the award of the degree of Bachelor of Civil Engineering Faculty of Civil Engineering Universiti Teknologi Malaysia

5 5

6 6 I declare that this thesis is my own work except for the quotations and summaries of which I have explained the sources. Signature :. Author : WAN NORSHUHADA WAN KHAIRUDDIN Date : 23 APRIL 2007

7 7 To my beloved parent and my siblings Wan Khairuddin Wan Abd. Kadir and Salbiah Mat Yusof Wan Norshakira Wan Norshahezan Wan Mohd Ameer Faisal Wan Mohd Faisal Faes Wan Norshakila And unforgettable to my special one Mohd Azamin Abd.Rahman May Allah bless you..!!

8 8 ACKNOWLEDGEMENT Praise be to Allah S.W.T, the Most Gracious, the Most Merciful for all the blessings and guidance upon me thoroughly my study. While the motivation and hard work in pursuing a degree s must come from within, interactions with others have stimulated and sustained me personally during my studies. I want to acknowledge many people whose professional help and personal support has made it possible for me to complete this final project. I feel gratitude to Associate professor Dr. Nordin Yahaya, my final project supervisor, for all guidance, knowledge and help he has extended to me. I would like to express my gratefulness to my family for their continuous love and support throughout my life. Finally, I wish to thank my all friends for their support through this final project.

9 9 ABSTRACT The main function for marine pipeline is to transporting hydrocarbon fluid such as crude oil and natural gas from one location to another location. But, the main problem for subsea pipeline is corrosion attack, which could affect the pipeline system integrity. The current practice in pipeline corrosion prevention is using the cathodic protection (CP) system, which is primarily intended to protect metals permanently exposed to seawater or marine sediments. CP is often fully effective in preventing any severe corrosion in a marine environment and has a corrosion reducing effect on surface intermittently wetted by seawater. This project is focused in design of external corrosion prevention of subsea pipeline using the cathodic protection system based on sacrificial anode and makes a parametric analysis for the CP method to determine parameters that affecting the design such as soil resistivity, design life, driving potential, weight of anodes and coating efficiencies. From the sacrificial anode method, the total number of anodes for the specific length of pipeline is determined. The research methodology consists of three

10 10 main stages, which are data analysis and evaluation, designing the spreadsheets and the sensitivity analysis of parameters involved in the design. From the sensitivity analysis found that the major parameters affecting the CP design are soil resistivity, design life, driving potential and coating efficiencies. The analysis and the concentration of these sensitivity parameters can be implemented to design the excellent CP system in future. ABSTRAK Fungsi utama struktur talian paip bawah laut adalah untuk mengalirkan bahan seperti gas dan minyak mentah dari tempat menggalian ke tempat penyimpanan. Tetapi, masalah utama yang dihadapi oleh struktur ini adalah serangan karat yang boleh menyebabkan sistem dan operasi struktur talian paip ini terganggu. Amalan biasa dalam industri struktur bawah laut dalam menangangi masalah pengaratan pada struktur ialah dengan menggunakan sistem cathodic protection (CP) yang mana berkesan dalam melindungi struktur dari mengalami pengaratan yang kritikal. Oleh yang demikian, kajian ini memfokuskan kepada rekabentuk sistem cathodic protection dan membuat analisis terhadap parameter-parameter yang mempengaruhi dalam rekabentuk. Dalam kajian ini, rekabentuk hanya akan dibuat berdasarkan sistem CP yang menggunakan kaedah sacrificial anode sahaja. Metodologi penyelidikan mempunyai tiga bahagian utama iaitu data analisis, rekabentuk spreadsheet dan menganalisis parameter yang mempengaruhi rekabentuk. Daripada analisis didapati parameter yang banyak

11 11 mempengaruhi rekabentuk ialah rintangan tanah, jangka masa operasi, kebolehan anod dalam rintangan pengaratan dan keberkesanan penyaduran. Dengan adanya analisis dan penekanan yang lebih terhadap parameter-parameter yang mempengaruhi dalam rekabentuk CP, diharapkan ia dapat menghasilkan sistem yang lebih baik pada masa akan datang. TABLE OF CONTENTS CHAPTER TOPIC PAGE TITLE DECLARATION DEDICATION ACKNOWLEDGMENT ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES i ii iii iv v vi vii xi xii

12 12 NOMENCLATURES ABBREVIATIONS TERMS APPENDICES xiii xv xvi xix I INTRODUCTION Preamble Background of the study Objective Scope of study 3 II LITERATURE REVIEW Design consideration Basic Requirement Site Iinvestigation Meteo-marine Data Design Wall thickness Determination Hydrodynamic Stability Free sspan Evaluation Corrosion Prevention and Insulation Bends, Components and Structure Concrete Coating Marking, Handling and Repair Fabrication Linepepe Production Internal Coating External Anti-corrosion Coating Anode Manufacturing 10

13 Anode Installation Concrete Coating Installation General Pipe Assembly Pipe Laying Trenching and Backfilling Pre-commisioning Operation General Operation, Maintenance and 13 Abandonment In Service Inspection Cathodic Protection System in Pipelines General Recommanded CP Potential Criteria principal of cathodic Protection System Choice of Cathodic Protection System methods of Applying Cathodic Protection Sacrificial Anode Method Impressed Current Method Sacrificial Anodes vs. 24 Impressed Currents Anodes Types of Anodes Anodes Material 28 III METHODOLOGY Flow of Study Codes and Standards 32

14 Spreadsheet Design of Cathodic protection Crack Propensity Ratio 39 IV RESULTS Design Parameter Spreadsheet Development Parametric Analysis General Driving Potential Soil Resistivity Weight of Anodes Design Life Coating Efficiencies 50 V DISCUSSION General Driving Potential Soil Resistivity Design Life Coating Efficiencies 57 VI CONCLUSIONS 58 REFERENCES 59 APPENDIX 61

15 LIST OF TABLES 15

16 16 TABLE NO. TITLE PAGE 2.1 Current Density Ratio for Thin-film Coated Structure Current density ratio for pipeline coatings and 9 pipeline heat insulation coatings. 2.3 Galvanic series of some metals in sea water Parameters related in CP design Table for Geotechnical Information Anode parameters Services parameters Other Parameters Related to Design CP Driving potential in different type of reference electrode Different number of anodes based for different soil resistivity A different number of anode based on weight Number of anode based on design life Number of anode related to the coating efficiency Recommended Potentials for Protection of Fixed 54 Offshore Steel Platform (Veritas) 5.2 Approximate relationship between soil resistivity 56 and soil corrosivity LIST OF FIGURES

17 17 FIGURE NO. TITLE PAGE 2.1 Anodic and cathodic reactions at metal surface Kinetics of anodic and cathodic reactions Diffusion- controlled reduction of oxygen Cathodic protection anodes system Bracelet for anode attachment Study flow chart Sacrificial anodes CP design flowchart Example of spreadsheet for input Parameters Example spreadsheet of number of anode calculation Example of spreadsheet of anode s number and the anode spacing for specific length of pipe Number of anode based on the driving potential in different referred electrode Soil resistivity versus Number of Anodes Weight of Anode versus Number of Anode Design life versus Number of Anode Relationship between coating efficiencies with the number of anode Determination of protection potential for steel 55 in sea water.

18 BB - 18 NOMENCLATURES OD - Outside Diameter ID - Pipe Inside Diameter I corr - Corrosion current E corr - Corrosion potential E I - Rate Potential at point 1 E 2 - Poisson s Ratio I 1 - Cathodic Current at point 1 I 2 - Cathodic Current at point 2 I - Changes value of cathodic current Aw - Wetted parameter of pipe I c - Cathodic Current Demand CE - Coating Efficiencies I - Required current A - Total area of pipe R T - Curcuit Resistance Rc - Structure to Electrolyte resisatnce R - Soil resistivity Ra - Anode to structure resistance W - Minimum net anode mass W - Weight of single anode E - Anode consumption rate Mean coating breakdown factor L - Total length of pipeline requiring protection μ - Anode utilization factor J - Mean current density A s - Pipe surface between anodes

19 19 r - Anode resistance ρ - Seawater resistivity A - Anode s exposed surface area V - Potential difference between the anode and the bare steel ID - Bracelet anode inner diameter T - Bracelet anode thickness L - Bracelet anode length L - Design life of pipeline Î - Length backfill column D - Diameter backfill column

20 20 ABBREVIATIONS CP DNV DC FBE GBSS NACE RP UTS Cathodic Protection Det Norkse Veritas Direct current Fusion Bonded Epoxy Gypsum-Bentonite-Sodium Sulfate National Association of Corrosion Engineers (USA) Recommended practice Ultimate Tensile Stress

21 21 TERMS Asphalt See Bitumen Anode Electrode from which electric current flows to an electrolyte (water, soil). On the surface an oxidation process takes place, e.g. metal ions or hydroxyl ions to oxygen and water Backfilling Covering of trenched pipeline, which nay be natural (by sedimentation) or artificial (by rock dumping or by mechanically returning the seabed material removed during trenching) Bend Curved piece of pipe, for offshore use either hot formed from induction bent linepipe joints (motherpipe) or forged items. Bends with small bending radius (1.5 x ID or less) are also referred to as elbows, and will normally be forged. To facilate the welding into pipeline, bends are normally provided with short, straight sections (tangent length).

22 22 Bitumen Coating material derived from distillation of hydrocarbons or extracted from natural deposits (asphalt). Buckle Deformation of pipeline as a result of local actions or stability failure of the pipe section due to external pressure, possibly in combination with bending. The buckling may lead to water entering the pipeline (wet buckle) or not (dry buckle). Cathode Electrode into which electric current flows from electrolyte (water, soil). On the surface a reduction process takes place, e.g. water to hydrogen and hydroxyl ions. Cathodic Protection Reduction of corrosion rate by shifting the corrosion potential of the electrode toward a less oxidizing potential by applying an external electromotive force. Cathodic disbonding Loss of bond between barrier coating and steel substrate due to the formation of hydroxyl ions in connection with cathodic protection. Coal tar Coating material manufactured by distillation (pyrolysis) of rock coal. Coating yard Onshore facility for the application of pipe coatings and sacrificial anodes to pipe joints. Concrete coating Pipe coating of reinforced concrete, applied to increase the pipeline weight and/ or protect the steel pipe and its anti-corrosion coating against mechanical damage.

23 23 Corrosion allowance Increase of the wall thickness corresponding to the expected corrosion loss, with the objective of ensuring the required wall thickness during the services life. Enamel Hot applied pipe coating consisting of bitumen or coal tar, reinforced with layers Epoxy paint Two-components paint consisting of epoxy resin and solvent. Galvanic Anode A metal, which, because of its relative position in the galvanic series, provides sacrificial protection to metals, those are more noble in the series, when coupled in an electrolyte. Galvanic Cathodic Protection System: A cathodic protection system in which the external electromotive force is supplied by a galvanic anode. Groundbed One or more anodes installed below the earth s surface for the purpose of supplying cathodic protection. Impressed Current Cathodic Protection System A cathodic protection system, which the external electromotive force is provided by an external DC power source. Linepipe Steel material for welded pipelines Rectifier

24 24 A device that converts alternating current to direct current. Sacrificial anode An anode that connected to structure can offer cathodic protection while it is consumed. LIST OF APPENDICES APPENDIX TITLE PAGE A Hand Calculation for Cathodic Protection Design 61

25 CHAPTER I INTRODUCTION 1.1 PREAMBLE The objective of marine pipeline is to transporting hydrocarbon fluid such as crude oil and natural gas from one location to another location. The establishment of marine pipelines is a more recent development of the latter part of the twentieth century [1]. As a part of an offshore system, offshore pipelines form a major link to link the offshore oil fields with offshore facilities. Therefore, pipelines have become one of the large financial assets for the pipeline operator. Moreover, maintaining the high reliability of the pipelines has become a great concern. The importance of offshore pipelines will continue to increase in the near future. Marine pipeline can be divided into different types, depends on the types of medium to transport. The marine pipeline design construction begin from the first step from designs based consist of the basic requirements related to functionality of pipelines, selection of material relevant for design and installation, analysis of loads and force incurred during installation, fabrication of individual pipe joints, include pipes production, anode manufacture and anti-corrosion coating process,

26 2 pipelines installation, control and documentation through the design installation, operation of pipelines, and lastly repair and maintenance of pipelines. The steel may have as good mechanical properties as possible, but one thing is always inherently lacking in carbon steels: corrosion resistance. The outside of the steel may be protected by coating and cathodic protection, but in case of the transport of corrosive commodities there is a need efficient corrosion control systems. 1.2 BACKGROUND OF STUDY For pipelines operating at elevated pressure and temperature internal corrosion may be serve problem when water is present in the stream, which is typically the case for pipelines. Recent studies relating to loss of containment of pipeline indicates that corrosion is one of the dominant failure modes of steel pipe [4]. The reaction from corrosion will suffer the pipelines that may reduce the pipe strength and durability [1]. There are many types commonly used for corrosion protection such as coating, cathodic protection and corrosion allowance but the commonly used for pipeline is cathodic protection method. From the recent investigation has found that the CP design is dependent on a many parameters such as current density of anodes, soil resistivity, driving potential, design life, weight of anodes, pipes resistivity, seawater temperature, coating types, coating efficiencies and etc. [8]. However, for this study the only basis parameter will be analyzing such as soil resistivity, driving potential, design life, coating efficiencies and weight of anodes. This study only considers a design of cathodic protection of sacrificial anode method only and used a standard of DNV and NACE as guidance.

27 3 1.3 OBJECTIVES OF STUDY The objectives of study are; 1. To study overview process of pipeline design. 2. To prepare a spreadsheet for the design of cathodic protection in pipeline. 3. To determine factors effecting the efficiency of the design 1.4 SCOPE OF STUDY The scope of study including overview of the oil and gas pipelines from the design aspects, design stage, fabrication, installation, operation, and maintenance. This study also covers about the cathodic protection system design of pipelines and preparing the spreadsheet of cathodic protection method. The last topic is to analyze of the parameters effecting of the CP design.

28 4 1.5 SIGNIFICANT OF STUDY Corrosion can be a very big problem to pipelines, because its can reduce the system integrity of pipeline. To ensure the proper flow of the transported medium and to extend lifetime of pipeline, it is important to have adequate corrosion prevention. However, the effectiveness of the prevention system will depend on the method used in the design. The outcome of this project highlighted the factors affecting of the CP design.

29 CHAPTER II LITERATURE REVIEW 2.1 DESIGN CONSIDERATION Basic Requirements The bases for design consist of the basic requirements functionality, as well as a description of the environment into which pipeline will be placed, leading to selection of pipeline dimension and routing. Other main requirements also design are pipe properties, diameter, steel grade options and linepipe specification detail, including supplementary requirements to codes and guidelines. The important things in design to consider are parameters related to flow assurance and pressure containment, i.e. design temperature

30 6 and pressure, maximum and minimum operating, functional or operational of pipeline, authorities requirements, environmental impact Site Investigation Site investigation such as geophysical survey, geotechnical survey, soil sampling and in-situ testing and laboratory testing are established to obtain reliable data for the design, construction and subsequent operation and maintenance of the pipeline associated structures Meteo-marine Data The acquisition of meteorological and hydrographic data of relevance for the pipeline project is traditionally referred to as environmental investigation. The objective is to established hydrographic data and parameters to be used in pipeline design, installation and operational of marine pipeline. The most important data described wave, current and water level conditions, water temperature and salinity.

31 7 2.2 DESIGN Wall Thickness Determination The objective of the pipeline design is to determine the optimal wall thickness and steel grade of pipe. The wall thickness will be selected following a simple hoop stress calculation. The design of the pipeline wall thickness is based on the classification of the pipeline into safety classes, based on location and transport medium. Some designs also considered a trawl impact, trawl hooking and pull-over, external pressure only, and propagation buckling. The wall thickness design may result in pipe that is too thin-walled for practices use, or rather for comforts Hydrodynamic Stability On-bottom stability analysis is performed to ensure the stability of the pipeline when exposed to wave and current forces and other external loads. The procedure for onbottom stability included determination of near seabed flow conditions, determination of hydrodynamic forces and soil reaction forces and hydrodynamic stability check. Pipe and soil interaction is important for the stability of the pipeline on the seabed in the horizontal, as well as the vertical direction

32 Free Span Evaluation Free span analysis based on generally acceptable static and dynamic calculation methods. The free span shall have adequate safety against failure such as excessive yielding, fatigue, buckling and ovalisation. The free span data includes the pipe data, functional data, hydrographic data and geotechnical data. The analysis of loading also considered the static analysis, dynamic analysis, and fatigue analysis Corrosion Prevention and Insulation Internal corrosion of pipeline depends upon the aggressiveness of the transported medium and may be prevented by inhibitor injection, internal coating or the use of corrosion resistant alloy [2]. Coating of the steel surface protects against corrosion by creating physical barrier between the pipe and the electrolyte oxygen from reaching the steel. Cathodic protection also is considered the principal corrosion prevention Bends, Components and Structure Components included fittings and special components, formed passive parts of the pipeline system. This component is those may be actuated in connection with pipeline operation, such as valve that may be closed.

33 Concrete Coating The most commonly method of application of concrete is by impingement, a process whereby a fairly dry concrete mix is thrown at a rotating pipe. The other methods include wrapping concrete around the pipe Marking, Handling and Repair The finished coated pipe joints are stored at the coating yard; all the pipes must be marking to allow unambiguous identification of the individual pipe joint, including its history of coating, repair, and anode attachment. 2.3 FABRICATION Linepipe Production Linepipe production is the delicate economic and difficult technical decision to design up-front the chemistry and subsequent steel making processes, refining steps, casting sequence, rolling scheme and pipe forming procedure.

34 Internal Coating Internal coating of the pipeline may be specified to prevent internal corrosion, to resist erosion, or to reduce the flow resistance. The most common internal anti-corrosion coating is Fusion Bonded Epoxy (FBE), and epoxy paint. For coated structures where the coatings are selected and applied according to NORSOK Standard M-501 Surface Preparation and Protective Coating [5]. The current densities given in clause 5.1 of NORSOK Standard M-501 may be multiplied by a factor given in Table 2.1. The values in Table 2.2 shall be used for pipelines and when these coatings are used on items other than pipelines. The coating quality should be according to commonly applied industry standards. Table 2.1: Current density ratio for thin-film coated structures. Design life, Mean Final years Table 2.2: Current density ratio for pipeline coatings and pipeline heat insulation coatings. Design life, year Asphalt + concrete Rubber Polypropylene Mean Final Mean Final Mean Final

35 External Anti-corrosion coating External polyolefin coatings may be applied at the pipe mill as they are resistant to handling and transport damage. Most commonly use is asphalt enamel, three layer polyolefin coating, fusion bonded epoxy and elastomer coating Anode Manufacturing Sacrificial anodes for marine pipeline is normally of the bracelet type, i.e. cylindrical shell around pipe joint, and are produced by specialist anodes manufactures. When the anodes are installed on the individual pipe joints in a coating yard the mounting involves welding of protruding reinforcement straps of both sort Anode Installation Sacrificial anode type cathodic protection systems provide cathodic current by galvanic corrosion. The current is generated by metallically connecting the structure to be protected to a metal/alloy that is electrochemically more active than the material to be protected. (Both the structure and the anode must be in contact with the electrolyte.) Current discharges from the expendable anode, to the electrolyte, and onto the structure to be protected.

36 Concrete Coating The most commonly method of application of concrete is by impingement, a process whereby a fairly dry concrete mix is thrown at a rotating pipe. Other methods include wrapping concrete around the pipe Marking The finished coated pipe joints are stored at the coating yard; all the pipes must be marked to allow unambiguous identification of the individual pipe joint, including its history of coating, repair, and anode attachment. 2.4 INSTALLATION General Marine pipeline installation comprises all activities following the fabrications of the pipe joints, bends and components through the preparation of the pipeline commissioning. Prior to the installation activities, a proper survey must be carried out to determine the route and alignment of the pipeline. Several offshore installation methods can be envisaged, depending on the pipeline characteristics (diameter, length, water depth) and the availability of suitable equipment such as conventional pipelaying (Scurve), reeling, towing following assembly onshore (on-bottom, off-bottom, mid-depth and surface), and J-laying.

37 Pipe Assembly The individual pipe joints are assembled into pipe strings by girth welding. The welding can be carried out offshore during pipelaying, often referred to as marine welding. There are many processes considered for modern girth welding of pipeline such are; i. Friction welding ii. Explosion welding iii. Laser welding iv. Submerge arc welding, SAW v. Shield metal arc welding, SMAW vi. Gas metal arc welding, GMAW. After the strings are joined to other pipe strings, or to riser, valve assemblies, etc., mechanical connections may be used as alternatives to welding, whether hyperbaric or above-water. After welding the linepipe steel, the weld area and the adjacent coating cutback is protected by field joint coating Pipe Laying Commonly used method of pipeline installation is using laybarge, where welding individual pipe joints into pipe strings produce the pipeline offshore, which is paid out from the laybarge to the seabed. Depending upon the shape of the suspended pipe, a recent method to install pipe by use a J-lay and S-lay method. A laybarge is a floating factory where the pipe joints are welded on to the pipeline as it is installed. From the

38 14 laybarge the pipeline described an S-curve to the seabed and approximately for water depth less than 700m. However, J-lay is conditions where pipes string enters the water in a vertical or nearly vertical position and suitable for water depth exceed than 700m Trenching and Backfilling Trenching is a process to install the pipes permanently below the natural seabed to protect the pipeline from hydrodynamic forces, to protect the pipeline against mechanical damage, to eliminate or reduce free spans, to prevent upheaval buckling, and to increase thermal insulation of the pipeline Pre-commissioning Pre-commissioning covers all activities from performance of the acceptable pressure test, normally part of the scope for the installation contractors, up to filling the competed pipeline with product and the commencement of product transportation. The activities included flooding and hydro testing, gauging, cleaning, de-watering, drying, and nitrogen purging.

39 OPERATION General The operation and maintenance procedure should, at a minimum provide information with respect to organization and management, start-up and shut-down procedures, operational limitations, identification all items to be monitored, inspect and maintenance, pigging requirements Operation, Maintenance and Abandonment Pre-commissioning activities are hydrostatic pressure testing, cleaning of pipe with is components, gauging, and drying. Maintenance pipeline should consider as-built condition, results from start-up periodical and additional surveys, predicted inspection time interval, relevant legislation and statutory authorities. Changes in the design condition includes the changes of pipeline system include; change in environmental data, change of functional data, extension of design life, modification due to new developments in the vicinity, and damage to pipeline system will affect the system operation [3]. Liquids may be pumped, or pigged, out of the pipeline using water or insert gas. If the pipeline is to be abandoned it should be decommissioned, disconnected from other installations and left in a safe condition.

40 In-service Inspection The factors to be considered for subsequent inspection surveys are; verification that the required overburden is present along pipelines, inspection and measurement of pipeline expansion and riser displacement caused by pressure and thermal effects, visual inspection of mechanical couplings and flange connections, leak detection, verification. That operational parameters are within acceptable limits, verifications that instrumentation is properly installed and its functioning. The time gap between first inspection and frequency of future inspection is determined based on various factors such as the potential corrosive effect of the fluid, the detection limit and accuracy of the inspection system, results from previous inspection, and changes in the operation parameters for the pipeline system 2.6 CATHODIC PROTECTION SYSTEM IN PIPELINES General Corrosion is defined as a destructive attack on the metal by a chemical or electrochemical reaction with its environmental [3]. The driving force is tendency for refined metal return to a natural state characterized by a lower level of internal energy. In the case linepipe steel, the iron will tend revert to its natural state as ferrous oxides (iron ore). Internal corrosion of pipeline is depends upon the aggressiveness of the transported medium, and may be prevented by inhibitor injection, internal coating or used of corrosion resistant alloys. External corrosion of a pipeline in seawater is an electrochemical process. A galvanic element is created where an electric current flows

41 17 between an anodic area and a cathodic area, with the seawater acting as an electrolyte. Coating the steel surface protects against corrosion by creating a physical barrier between the pipe and the electrolyte, preventing oxygen from reaching the steel. Cathodic protection, on the other hand, renders the steel immune to corrosion by lowering the electrical potential Recommended CP potential criteria Offshore steels in aerobic environments can be protected from oxygen corrosion by depressing the steel to potentials below -800mV (Ag/AgCl) whereas for steels in anaerobic environments the criterion potential is -950mV (Ag/AgCl) [4]. However, it is possible to overprotect steel. In fact, overprotection may be as detrimental as under protection. As the potential is reduced below about -1000mV (Ag/AgCl) the risk of hydrogen cracking increases hence reducing the fatigue properties [4]. To prevent this occurrence, a lower limit of potential has been set at -1100mV (Ag/AgCl) [4]. For very high strength steels with ultimate tensile stresses (UTS) in excess of 700 N/mm 2, which are susceptible to hydrogen cracking, the lower limit of the cathodic protection potential for these materials is set to -1000mV (Ag/AgCl) [4].

42 Principal of Cathodic protection system Corrosion is a non-stop process by an electrochemical reaction, and an anodic and cathodic electrochemical reaction is occurring simultaneously. Anodic reactions involve oxidation of metal to its ions, e.g. for steel the following reaction occurs. Fe > Fe2+ + 2e (2.1) The cathodic process involves reduction and several reactions are possible. In acidic water, where hydrogen ions (H+) are plentiful, the following reaction occurs as shown in equation 2.2. But, in alkaline solutions, where hydrogen ions are rare, the reduction of water will occur to yield alkali and hydrogen as an equation H+ + 2e > H2 (2.2) 2H2O + 2e > H2 + 2OH- (2.3) However, unless the water is desecrated reduction of oxygen is the most likely process, again producing alkali at the surface of the metal. O2 + 2H2O + 4e > 4OH- (2.4) Equation (2.1) and (2.2) are shown schematically in Figure 2.1 where anodic and cathodic sites are nearby on the surface of metal. We can change the rate of these two reactions by withdrawing electrons or supplying additional electrons to the metal. It is an established principle that if a change occurs in one of the factors under which a system is in

43 19 equilibrium, the system will tend to adjust itself so as to annul, as far as possible, the effect of that change. Thus, if we withdraw electrons from the piece of metal the rate of equation (2.1) will increase to attempt to offset our action and the dissolution of iron will increase, whereas equation (2.2) will decrease. Conversely, if we supply additional electrons from an external source to the piece of metal, equation (2.1) will decrease to give reduced corrosion and equation (2.2) will increase. The latter case will apply to cathodic protection. Thus, to prevent corrosion we have to continue to supply electrons to the steel from an external source to satisfy the requirements of the cathodic reaction. Note that the anodic and cathodic processes are inseparable. Reducing the rate of the anodic process will allow the rate of the cathodic process to increase. These principles may be expressed in a more quantitative manner by plotting the potential of the metal against the logarithm of the anodic and cathodic reaction rates expressed as current densities. Typical anodic and cathodic curves are illustrated in figure 2.2. The corrosion current, Icorr, and the corrosion potential, Ecorr, occur at the point of intersection of the anodic and cathodic curves, i.e. where anodic and cathodic reactions rates are equal. If electrons are pumped into the metal to make it more negative the anodic dissolution of iron is decreased to a negligible rate at a potential E I, whereas the rate of the cathodic current is increased to I 1. Hence, a current I 1 must be supplied from an external source to maintain the potential at E 1 where the rate of dissolution of the iron is at a low value. If the potential is reduced to E 2 (Figure 2.1) the current required from the external source will increase to I 2. Further protection of the metal is insignificant, however, and the larger current supplied from the external source is wasted. The metal is then to be over-protected. In aerated neutral or alkaline solutions the cathodic corrosion process is usually the reduction of the oxygen.

44 20 Anodic reaction (1) Cathodic reaction (2) H + Fe 2+ H 2 +2e -2e metal e e Figure 2.1: Anodic and cathodic reactions at metal surface E Anodic reaction (1) E corr I 2 E 1 I 1 E 2 cathodic reaction Irr Log 1 Figure 2.2: Kinetics of anodic and cathodic reactions

45 21 The kinetics of this cathodic process are controlled by the rate at which oxygen can diffuse to the surface of the metal, which is slower than the rate of consumption of oxygen by the cathodic reaction. Thus, the rate of this reaction does not increase as the potential of the metal is made more negative but remains constant unless the rate of supply of oxygen to the surface of the metal is increased. The influence of flow velocity on cathodic protection parameters is illustrated in figure 2.3. A current of I 1 is initially required to maintain the metal at the protection potential E 1. However, if the flow rate is increased the limiting current for the reduction of oxygen is increased (dotted line) and the current required to maintain the metal at the protection potential is increased by I. Thus, the current density required to maintain the correct protection potential will vary with service conditions. Clearly, cathodic current density is not a good guide as to whether a structure is cathodically protected. The correct protection potential must be maintained if corrosion is to be prevented. If the structure is over-protected and the potential is reduced to a potential region where reduction of water (equation 2.4) can take place, further current will be required from the external source and current will be wasted. In Figure 2.3 reducing the potential from E 1 to E 2 will increase the current required from the external source from I 1 to I 2 as a result of an increased rate of reduction of water. Excessive negative potentials can cause accelerated corrosion of lead and aluminium because of the alkaline environments created at the cathode. These alkaline conditions may also be detrimental to certain paint systems, and may cause loss of the paint film. Hydrogen evolution at the cathode surface may, on high-strength steels, result in hydrogen embrittlement of the steel, with subsequent loss of strength. It may also cause disbanding of any insulating coating: the coating would then act as an insulating shield to the cathodic protection currents.

46 22 Figure 2.3: Diffusion- controlled reduction of oxygen Choice of Cathodic Protection System For the cathodic protection of land based buried pipelines an impressed current system is preferred. The type of cathodic protection system to be applied (i.e. sacrificial anodes or impressed current) shall be as indicated on the requisition. If not specified, the Contractor shall select the type of cathodic protection and shall justify his choice in his basic design. The following factors should be considered when making the selection. i. Soil resistivity ii. Total current demand iii. Economic considerations

47 23 iv. Presence of stray currents v. Availability of power supply vi. Site layout vii. Presence of other conductors viii. Maintenance ix. Possibility to use existing, principal owned cathodic protection systems. If the above factors do not clearly justify one particular system, impressed current shall be used. If stray currents may influence the pipeline under protection, impressed current shall be applied Methods of Applying Cathodic Protection. Cathodic protection may be achieved in either of two ways. By the use of an impressed current from an electrical source, or by the use of sacrificial anodes (galvanic action) Sacrificial Anode Method To understand the sacrificial anodes for cathodic protection system, it is necessary to have in mind the galvanic series of metals. The galvanic series for a few selected metals in seawater is shown in Table 2.2. When the tendency for metal to go

48 24 into solution as metal ions increases (leaving an excess of electrons on the metal surface), i.e. M > M+ + e (2.5) the metal becomes more electronegative [10]. Thus, since zinc, aluminium and magnesium are more electronegative than steel they are increasingly able to supply electrons to the more electropositive steel when in electrical contact in water, and will effect cathodic protection of the steel surface. Clearly, if steel was coupled to copper in seawater, steel would supply electrons to copper, which would become cathodically protected, and the corrosion of the steel would be enhanced. The cathodic protection of a steel pipe with sacrificial anodes is illustrated in Figure 2.4. Electrons are supplied to the steel pipe, via the electrical connection, and a corresponding amount of anode material goes into solution as metal ions, according to the laws of electrolysis. Some anode material is lost by self-corrosion, and the anodes are not converted to electrical energy with 100% efficiency. Zinc, aluminium and magnesium area the metals commonly used for sacrificial cathodic protection. The driving voltage of sacrificial anodes is now compared with impressed-current anodes, and sacrificial anodes must be located close to the structure being protected. Although almost any piece of zinc could provide cathodic protection over a short period of time, cathodic protection schemes are usually required to operate over periods of several years. Anodes can lose their activity and become passivated, developing a non-conducting film on their surfaces so that they no longer are able to supply current. This can be avoided by careful control of the concentrations of trace impurities in the anode materials, and by alloying. For zinc anodes the level of iron, for example, must be kept below 0.005% for satisfactory long-term operation of the anodes. To prevent passivation of aluminium anodes, alloying with, for example, indium has been found to be successful. The previously successful alloy with mercury is now disliked on environmental grounds.

49 25 Table 2.3: Galvanic series of some metals in sea water Electropositive Platinum Titanium Stainless steel Monel Copper Lead Iron, cast iron, or steel Cadmium Zinc Aluminium Magnesium Electronegative More Electropositive Structure without sacrificial anode CP method Structure with sacrificial anode CP method Figure 2.4: Cathodic protection anodes system

50 Impressed Current Method In this method, the driving voltage is provided by a power supply. If a DC power supply is all available, the power will first need to be rectified. The terminals are then connected to the cathode and to the auxiliary electrode (the anode). When the impressed current method is used to protect structures buried in soils, the auxiliary electrode can be an electronically conductive metal. For this, scrap iron or graphite is frequently used. It is also common practice to place a conductive backfill in the area around the anode material in order to reduce the resistance of the soil around the anode. A range of materials has been used as non-consumable anodes for impressed-current systems. The sorts of properties required by these anodes are; i. Good electrical conduction, ii. Low rate of corrosion, iii. Good mechanical properties, able to stand the stresses which they may be subjected to during installation and in service, iv. Readily fabricated into a variety of shapes, v. Low cost, vi. Able to withstand high current densities at their surfaces without forming resistive barrier oxide layers, etc.

51 Sacrificial Anodes vs. Impressed Currents The sacrificial anode technique and the impressed current method have their individual strengths and weaknesses. The advantages of sacrificial anodes are: i. They operate independent of a supply of electrical power ii. They are simple to install and if adequate protection does not occur at commissioning, additional anodes are often easy to install iii. They cannot be incorrectly attached to the structure iv. There is no control function to be exercised. The advantages of the impressed current techniques include: i. That it is possible to have a large driving voltage so that it may be used to protect large, even uncoated, structures in high receptivity environments ii. It needs comparatively few anodes iii. The voltage may be tuned to control the performance of the system. The most severe limitation of the sacrificial anode method is the small driving force that restricts its use to conductive environments, short current throws and marine use only. By contrast, the disadvantages of the impressed current system are the need for a reliable DC power supply, the danger of overprotection if the system is badly tuned, the difficulty of achieving a satisfactory potential profile over a complex shape. There are some inherent dangers in using the impressed current method, as it is possible to connect the terminals the wrong way round inadvertently. If this occurs, instead of reducing the corrosion rate, the corrosion will increase dramatically.

52 Anodes Types of anode There are many type of anodes that be used in cathodic protection depends on the type of groundbeds, soil resistivity, voltage accuracies etc. i. Graphite Anodes: Commonly used for impressed current systems and to protect undergroundbed structures. Suitable for deep, shallow vertical, or horizontal groundbeds with carbonaceous backfill. ii. High Silicon cast iron anodes: Used widely in underground application in both shallow and deep groundbeds, especially in high silicon cast iron anodes and seawater. iii. Platinized Niobium/Tantalum anodes: Used when high driving voltage is required. Take advantage of the properties of platinum, but avoid the low driving voltage restriction of platinized titanium anodes. iv. Platinized Titanium anodes: Take advantage of the low consumption rate and high current density. Voltages in excess of 10 Volts will result in severe pitting of the titanium core causing premature failure. v. Magnetite anodes: Quite expensive but have an extremely long life. They are therefore an economical choice for some applications. vi. Mixed Metal Oxide anodes: Consist of a high purity titanium substrate with an applied coating consisting of a mixture of oxides. The titanium serves as a support

53 29 for the oxide coating. The mixed metal oxide is a crystalline, electrically conductive coating that activates the titanium and enables it to function as an anode. When applied on titanium, the coating has an extremely vii. Low consumption rate, measured in terms of milligrams per year. As a result of this low consumption rate, the tubular dimensions remain nearly constant during the design life of the anode - providing a consistently low resistance anode. viii. Bracelet anodes: Subsea pipeline are normally used a bracelet anodes, supplied as two half bracelets. The half bracelet may be half shell of anodes material or segmented anodes, considering of slender anodes welded to a steel bracelet as shown in Figure 2.5. Depending on the design the two halves are connected by bolting or welding. The anodes should be installed so as to prevent slippage. It is recommended to use an epoxy coating on the inner surface of the bracelet anode facing the pipe, to the surface facing the concrete coating and to the exposed parts of the bracelet anode. The anode shall be installed over the anti-corrosion coating. Any cut-outs in the coating to attach electrical connected shall be replace similar to the original. Dimensional tolerances shall conform to NACE RP0492.

54 30 Figure 2.5: Bracelet for anode attachment Anode s Material a. Aluminium alloys Aluminum Alloy anodes are limited to use in seawater or very brackish water use (must have more than 1000 ppm chloride ion concentration for Indium alloyed material and 10,000ppm Cl- for Mercury alloyed material. Aluminum Anode operates at approximately 95% efficiency yielding approximately 1250 amp-hrs-lb or a consumption rate of approximately 6.8 lbs./amps-yr in seawater applications only [9]. This efficiency may drop in half or more in brackish waters. There are lots of advantages Aluminium anodes that are;

55 31 i. Low driving potential (e.g volts to protected steel) ii. Lowest Galvanic Anode Cost ($ per Ampere-Year of current generated) iii. Are never used with select backfill and thus are installed as bare ingots. They typically are mounted to the structure they are intended to protect via their integrally cast galvanized iron core straps, pipes or rod b. Magnesium Alloys Anodes. Magnesium alloys is the highest operating Voltage of all common Galvanic Anodes but has the lowest efficiency and highest cost per ampere year of current flow. Typically used in soils and waters with resistivities higher than 1500 ohm-cm [9]. The electrochemical properties of Magnesium Anodes are; i. Ampere Hour/Pound Consumed Theoretical ii. Current Efficiency... 50% iii. Ampere Hours/Pound Consumed Practical iv. Pounds Consumed per Ampere-Year of Output...17 The advantages of Magnesium alloys for anodes application [9] are; i. Very high efficiency = >90% ii. Highest Available Driving Potential This is an advantage in higher resistivity soils. Generally this is the only applicable anode material in soils having a resistivity of 2000 ohm-cm or higher. iii. Lowest cost in terms of Dollars per Pound of Anode Metal and Lower in Cost vs. Magnesium Anodes in underground applications where soil resistivities are less than 2000 ohm-cm.

56 32 iv. Available for use both underground and under water applications but not generally recommended for us in salt water and soils less than 1000 ohm-centimeters resistivity due to short life in these environments. v. Available in the greatest number of sizes and shapes for many applications. vi. No temperature limitations (up to 212 F). vii. Select Backfill is not required although its use is highly recommended. If not used, lower efficiencies and selective attack of the magnesium metal will occur resulting in shorten anode operating life. viii. No danger of potential reversal except if alloy used is off spec (outside alloy permissible specification. ix. Will almost always have lowest total galvanic anode CP cost in environments with resistivities over 2000 ohm-cm when cost of installation is included in the evaluation. The only exception to this is when the current required for specific structures are only a few milliamperes total. Magnesium alloys limitations of are; i. Relative low efficiency = approximately 50% for all alloys except AZ- 63, Grade C which may be a low as 20% - 30%. ii. Most expensive common galvanic anode metal both in $dollar cost/pound of metal and material cost per ampere-year of corrosion protection provided. iii. Typically significantly higher material cost per ampere-year of cathodic protection provide than Aluminum Anodes in Seawater Applications. iv. Due to high driving potential, should not be used (except under very special.

57 33 c. Zinc Zinc Anodes were first used in 1826 by Sir Humphrey Davies to protect the copper cladding in seawater used on wooden ships in the English Navy [9]. This was the first use of cathodic protection to prevent corrosion of metal structures. Zinc was an ideal material in this environment because it has a very high operating efficiency and a relatively low driving voltage, which is an advantage in the very conductive (low resistivity) seawater [9]. Electrochemical Properties of Zinc are; i. Chemical composition ii. Current capacity Theoretical iii. 372 amp-hours/pound or 23.5 lbs. per amp-yr iv. Current efficiency above 90% underground and up to 95% in sea water v. Current capacity at 90% efficiency 335 amp-hours/pound or 26 lbs. per amp-yr vi. Potential in sea water or Select Backfill underground 1.1 volts vs. Sat. Cu-CuSO4 Two types of select backfill are commonly used with zinc anodes. The standard backfill has a higher resistivity and is general used with anodes to be installed in very conductive soils. The zinc anode advantages are; i. Very high efficiency = >90% ii. Low driving potential This is an advantage in low resistivity environments such as seawater, brackish waters and soils with resistivities less than 2000 ohm-cm.

58 34 iii. Lowest cost in terms of Dollars per Pound of Anode Metal and Lower in cost vs. Magnesium Anodes in underground applications where soil resistivities are less than 2000 ohm-cm. iv. Available for use both underground and under water (both salt and fresh waters. v. Available in many size and shapes for many applications vi. All of the design formulae and principals of design used with magnesium anodes apply equally with zinc. The zinc anode limitations are; i. Must not be used in applications where temperatures exceed 1200 Fahrenheit because inter-granular corrosion attack of the zinc will cause very premature failure of the material. ii. Susceptible to potential reversal if installed as bare anode material instead of installing with select GBSS Backfill in underground applications. Generally, this material should never be used underground except when installed with this Select Backfill. iii. Typically higher cost per ampere-year of cathodic protection provide than Aluminum anodes in seawater applications. Due to low driving potential, iv. Should not be used (except under very special circumstances) in soil resistivities greater than 2000 ohm-cm.

59 CHAPTER III METHODOLOGY 3.1 FLOW OF STUDY The flow chart shows in Figure 3.1 is the steps in the execution of these study. The objectives and the scopes of study are also being discussed after the determination of the title. The following step is the collection of information that related to the study from various sources such as conference paper, books, journal and related sources from the internet. Discussion has been carried out with supervisor on choosing the computer software to be used in the analysis and design of CP system.

60 CODES AND STANDARDS In marine pipeline there are many standard that widely recognized included; ASME B31G (B31G, 1984 AND 1991), SHELL-92, ISO 13623, BS 8010 Part 3 and DNV RP- F101 (DNV, 1999). For this study, all the parameters, equation, definition, commentary material, model equation, factors, classification, design consideration, etc. in pipeline, may be referred accordance to the DNV Standard RP-B401 Cathodic Protection Design 1993 and NACE Standard RP guideline, which is common used by designer in marine pipeline design. 3.3 SPREADSHEET For the analysis of data, spreadsheet is used because of the easy of use. By using a spreadsheet also easy to manipulate and friendly.

61 36 Gathered books and related resources related to the topic, also select code of practice to be used. Search and study the available data for CP design. Data analysis and evaluation. Design a spreadsheet Study on the parameters on the design of CP Conclusion Figure 3.1: Study flow chart 3.4 DESIGN OF CATHODIC PROTECTION The Figure 2.6 shows the methodology to determining the pipeline cathodic protection system design

62 37 1. Make sure that sufficient anode material is provided to satisfy the mean current demand over the design life of the system [5]. This criterion will determine the minimum total mass of anode required and is calculated using the mean values of current density and corrosion coating breakdown as follows: W = Z x E x J x B x πod x L (3.1) 100 μ Where: W = Minimum net anode mass (kg); Z = Design life (years); E = Anode consumption rate (kg/a years); J = Mean current density (A/m 2 ); B = Mean coating breakdown factor (%); OD = Outer diameter of steel pipe (m); L = Total length of pipeline requiring protection (m); μ = Anode utilization factor. 2. Calculate the net mass of anodic material required for each anode bracelet assembly. The sum of the individual anode mass must not only equal or exceed the minimum total mass requirement as calculated above, but each anode must be able to provide the necessary current output sufficient to guarantee protection based on initial and final design parameters [7]. 3. Calculate the current output requirement per anode spacing, which is dependent on the amount of exposed bare steel present between adjacent anodes and is calculated as follows [7]:

63 38 I = J x B x As (3.2) 100 Where; I = Initial/final current output required per anode (A); B = Initial/final coating breakdown factor (%); J = Initial/final current density (A/m 2 ); A s = Pipe surface between anodes (m 2 ) Assign all the parameters involved in design Estimate wetted surface area of pipes section, Aw (m 2 ) Calculate Cathodic Current Demand I c = (A)(I )(1.0-CE) Calculate total circuit resistance, RT = driving potential/i Calculate the structure electrolyte resistance, Rc = R/Aw Calculate max. allowable

64 39 groundbed resistance, Ra = RT-Rc Calculate number of anodes Estimate the spacing between anodes Figure 3.2: Sacrificial anodes CP design flowchart 3. Calculate the current output supplied by each anode is dependent on the anode resistance, which, for bracelet type anodes, is calculated using McCoy s formula [7]: Where: R = 0.315ρ (3.3) (A)^1/2 R = Anode resistance (ohm); ρ = Seawater resistivity (ohm-m); A = Anode s exposed surface area (m 2 ); 4 Determine the initial anode resistance, and to determine it the initial anode dimensions are used to calculate the exposed surface area of the anode. To determine the final anode resistance, it is first assumed that the anode mass has been consumed to its utilization factor, thereby resulting in final anode dimensions which are then used to calculate the exposed surface area of the remaining anode [5].

65 40 The current output (I ) for each anode is obtained using Ohm s Law, i.e. Where: I = V /R (3.4) V = Potential difference between the anode and the bare steel. To ensure satisfactory cathodic protection, the current outputs at the beginning and end of the anode design life must equal or exceed the initial and final current demands, respectively. Otherwise the size of the anode must be increased and/or the spacing reduced Crack Propensity Ratio The anodes dimension is limited to a certain length of thickness ratio to prevent the potential of the anode material cracking. The crack propensity check is calculated based on following formula: Crack Propensity Ratio (CPR)

66 41 CPR = π L x ID x 5T 3 (3.5) Where: ID = Bracelet anode inner diameter (mm) T = Bracelet anode thickness (mm) L = Bracelet anode length (mm) It is impossible to make adjusted until the ratio of inner diameter, thickness and length obtain a CPR value of 5 or less. This will ensure less probability of cracks during anode manufacture. The alloy selected for a sacrificial anode cathodic protection system should possess a sufficient negative potential to drive the structure to the required potential, high anode efficiency and an ability to remain active [4].

67 CHAPTER IV RESULT 3.1 DESIGN PARAMETER The parameters for the CP design as shown in Table 4.1 include the pipe parameters, geotechnical information, anodes parameters, services parameter and other parameters related to design. These parameters are very essential to be identified before the design process begins.

68 SPREADSHEET DEVELOPMENT SECTION OF PIPE LENGTH (ft) Table 4.1 Table of Pipe Parameters DIAMETER (ft) WETTED PERIMETER (ft 2 ) Defueling header Defueling return Supply line Refueling headers Hydrant lateral Table 4.2 Table for Geotechnical Information GEOTECHNICAL PARAMETER Soil resistivity 5000 Ohm-cm Table 4.3 Anode parameters ANODE PARAMETER Weight of anodes 10 Lb Current output of anode 1 Ma/ft2 Capacity of the anode 1230 Ahrs/kg Types of anodes Magnesium Driving potential -0.9 Volt Effective coating resistance 2500 Ohm/ft2 Coating efficiencies 30 %

69 44 Table 4.4 Services parameters SERVICES PARAMETER Design life Year 25 Table 4.5 Other Parameters Related to Design CP OTHER PARAMETERS Length backfill column 1.42 Ft Diameter backfill column 0.5 Ft For the design of CP, there are four major steps involved, which are; i. Parameter input used in the calculation ii. Calculation of the parameters that need for the next calculation based on the specify equation. iii. Number of anode calculation which use the previous result for the input iv. Graph plotting. Step 1 Data input of the CP design for pipelines such as geotechnical data, pipeline parameters, anode data and other additional parameters as Figure 4.1.

70 45 Input parameter. Figure 4.1: Example of spreadsheet for input Parameters Step 2 Calculation of the parameters such as current requirement, total circuit resistance, structure to electrolyte resistance, number of anode and spacing between anodes as shown in Figure 4.2 and the equation based on NACE Standard RP06-75 [7], was used as below; Cathodic Current demand;

71 46 I = (A)(I')(1.0-CE) (4.0) A = pipe area I' = current output of anodes CE = coating efficiencies Total circuit resistance (R T ) is given by equation; R T = A/I (4.1) Structure to electrolyte resistance, Rc is using the equation Rc = č/a. (4.2) č = effective coating resistance Maximum allowable groundbed resistance is given by equation; R T = Ra+Rw+Rc (4.3) Ra = Anode-to-electrolyte resistance Rw = Anode lead resistance (ignore) Number of anode; N = (p) (ln bl/d-1) (4.4) (Ra)(L)

72 47 I= (A)(I')(1.0-CE) Compare the number of anodes calculated based on design life and groundbed resistance and take a greater value as a final result. Number of anodes for the designed CP Figure 4.2: Example spreadsheet of number of anode calculation Step 3 From the calculation on step 2, the final number of anode for every section of pipe length and spacing of each anode are calculated as shown in Figure 4.3

73 48 N 1 =Pipe length 1 /area to be coverage Figure 4.3: Example of spreadsheet of anode s number and the anode spacing for specified length of pipe.