DESIGN AND INSTALLATION OF CATHODIC PROTECTION SYSTEM USING ZINC ANODE


DESIGN AND INSTALLATION OF CATHODIC PROTECTION SYSTEM USING ZINC ANODE    

TABLE OF CONTENT

LIST OF TABLES

LIST OF FIGURES

CHAPTER ONE            INTRODUCTION

1.1    Background of study………………………………………………………..….3

1.2    Problem statement………………………………………..……………………..4

1.3     Aim and objectives……………………………………………….…………….4

1.4     Significant of study…………………….……………..………………………..4

1.5     Scope of study………………………….…………………………...………….4

CHAPTER TWO        LITERATURE REVIEW

2.1    Introduction ……………………………………………………………………5

2.2    What is corrosion……………………….…………………..…………………..5

2.2.1    Corrosion reaction….…………………..………………………....5

2.2.2    Factors affecting corrosion (corrosion cell).………………………6

2.2.3    Corrosion of Steel…………………………………..………….…..6

2.3    Forms of corrosion………………………………………..………………..…..7

2.3.1    Soil and Water Corrosivity Factors……………….………………8

2.3.2    Soil Corrosivity……………………………………………………8

2.3.3    Water corrosivity………………………………………………….9

2.3.4    Factor Affecting Underground Corrosion…………………………9

2.4    Principle of cathodic protection………………………………………………..10

2.5    Method of applying cathodic protection system………………………….…....10

2.5.1    Impressed current cathodic protection……………………….……10

2.5.2    Sacrificial anode cathodic protection……………………………..12

2.5.3    Comparison table of the types of CP systems..………………..… 13

2.5.4    Protection criteria……………………………….…………………15

2.5.5    Limitations of cathodic protection system……………………..….15

2.5.6    Environmental parameters affecting cathodic protection………... 15

2.6    Cathodic protection system component…………………………………………16

2.6.1    Coatingsin Conjunction with cathodic Protection……….……. ...16

2.6.2    Reference Electrode……………………………………………… 16

2.6.3    Current Requirement Testing……………………………………...17

2.6.4    Soil Resistivity Measurement…………………………………...…17

2.6.5    Monitoring And Maintenance Of Cathodic Protection…………...19

2.7    Anode Resistance………………………………………………………………..19

2.7.1    Total Anode Resistance……………………………………………19

CHAPTER THREE        METHODOLOGY

3.1    Introduction…………………………………………………………………….21

3.2    General steps and evaluations………………………………………………….21

3.1.1    Cathodic protection criteria………………………………………..24

3.1.2    Design Parameters………………………………………………..24

3.3    Designing Test Rig……………………………………………………..........

3.4    Weighing Before and After Testing…………………………………………

3.5    Soil pH Testing………………………………………………………………

REFERENCES…………………………………………………………………………………..25

LIST OF TABLES

Table 2-1.Corrosivity of soils on steel based on soil resistivity………………………………..……...9

Table 2.2 Resistivity of some environment……………………………………………………….………9

Table 2.3 Anode materials for ICCP system…………………………………………………………….11

Table 2.4 Sacrificial Anode Materials …………………………………………………………………..13

Table 3.1 Some structure and their potential……………………………………………………………21

Table 3.2 Current density of some electrolyte…………………………………………………….…….23

LIST OF FIGURES

Fig. 1. Corrosion cell…………………………………………………………………………………..……5

Fig 2. Corrosion reaction………………………………………………………………………………..…6

Fig 3. Corrosion Cell Element…………………………………………………………………………..…6

Fig 4. Typical ICCP System………………………………………………………………………..………11

Fig 5. Sacrificial Cell……………………………………………………………………………………….12

Fig 6. Galvanic Anode Cathodic Protection System…………………………………………………...12

Fig 7. Cost Comparison of Cathodic Protection………………………………………………………..14

Fig 8.Wenner four-pin method for measuring soil resistivity ………………………………………….…18

Fig 9.Soil box method for measuring soil resistivity……………………………………………………..18

Fig 10. Anode resistance………………………………………………………………………...20

CHAPTER ONE:                  

INTRODUCTION

1.1 Background of the study

Cathodic protection (CP) is a method of controlling corrosion or a means of preventing corrosion of metaland can be applied to any buried and/or submerged metallic structures. It is normally used in conjunction with coatings and can be considered as a secondary corrosion control technique.

Cathodic protection can, in principle, be applied to any metallic structure in contact salty media(electrolyte). In practice its main use is to protect steel structures buried in soil or immersed in water. Structures commonly protected, includes:

      Cross country pipelines

      Exterior surfaces of pipelines immersed in water

      In plant piping

      Above ground storage tank bases

      Buried tanks and vessels

      Internal surfaces of tanks, vessels, condensers and pipes

      Well casings

      Foundation piling, steel sheet-piling

      Piling – tubular, sheet steel and foundation

      Marine structures including jetties, wharfs, harbours, piers

      Ships, hulls

      offshore platforms

      Reinforcing steel in concrete

Corrosion is a very serious problem. Three areas in which corrosion are important are in economic, improved safety and conservation of resources. The leakage of hazardous materials from a transport pipeline represents not only the loss of natural resources but also the potential for serious and dangerous environmental impact, and human fatalities. While pipelines are designed and constructed to maintain their integrity, diverse factors (e.g., corrosion) make it difficult to avoid the occurrence of leakage in a pipeline system during its lifetime.

All metals needs energy to be transformed from their oxide (natural) state to a refined state. The process of taking this energy away from the metal is called corrosion. Metals tend to revert back to their natural state when reacting with the environment. This corrosion reaction that occurs is an oxidation-reduction reaction. The purpose of cathodic protection is to stop this corrosive process.

Cathodic protection is the most important of all approaches to corrosion control techniques. One of the types of cathodic protection is sacrificial anode or galvanic cathodic protection. Corrosion occurs through the loss of the metal ions at anodic area to the electrolyte. Cathodic areas are protected from corrosion because of the deposition of hydrogen or other ions that carry current (Sandoval, A., et.al 2001). By using the sacrificial anode technique, the steel pipe will be protected from corrosion but the other metal which is the anode will corrode. In designing this method we must analyze parameters such as factor affecting corrosion, the amount of anode and rate of corrosion, the current densities and the total resistance.

Corrosion is an electrochemical process in which a current leaves a structure at the anode site, passes through an electrolyte, and reenters the structure at the cathode site. Differences in potential at different points along the pipe begin to develop. For example, because it is in a soil with low resistivity compared to the rest of the line, current would leave the pipeline at that anode site, pass through the soil, and reenter the pipeline at a cathode site. These potentials generate corrosion currents which leave the pipe to enter the soil at certain selective locations.

1.2 Problem statement

Despite many corrosion control method and inhibition techniques, there are still many challenges relating to cost effective operational performance, asset integrity management and maintenance of piping and other process equipment in the oil and gas industries due to corrosion effect.

Since carbon steel is commonly used in industrial units and for any buried and/or submerged metallic structures because of it’s low cost and excellent mechanical properties, it suffers severe corrosion attack in service.

Aside the detrimental effect of corrosion to humanity, it reduces the optimum transportation and delivery of crude oil and other products in the Oil and Gas industry. When this material (pipeline) comes in contact with salty media, corrosion will occur due to the loss of metal ions at the anodic area to the electrolyte, hence there is a need for a secondary corrosion control technique that will effectively prevent external corrosion of pipelines buried in the soil or water and to reduce material degradation rate.

1.3Aim and objectives

The main goal or aim of this work is to design and install a cathodic protection system as a secondary corrosion control technique for pipeline buried underground, using zinc anode.

The objectives in carrying out this study is to

investigate the effect of corrosion for underground steel pipeline Evaluate Factors affecting cathodic protection system underground The application of corrosion mitigation methods, particularly cathodicprotection Design acathodic protection system using sacrificial anode (zinc) for underground steel pipeline.

1.4 Significant of the study

Mitigating corrosion is important from both an operational and cost standpoint. Among other consequences, ignoring corrosion can shorten structure life, increase equipment or system out-of-service time, and increase maintenance cost. In addition to the dollar cost, the loss of critical material and human effort are also quite important. Measures such as cathodic protection help diminish such losses. It can also help to protect these structures from damaging. The need for cathodic protection system for pipelines cannot be overemphasized. When corrosion damages a pipeline and the content leaks out, it can destroy aquatic life, and this can in turn affect us as humans.

It is estimated that somewhere between 3 and 5 % of the gross national product (GNP) of industrialized countries is attributed to corrosion damage. Corrosion of metals costs the USA economy almost $300 billion per year and it is estimated that one third of this value could be saved with better selection of corrosion prevention techniques, including cathodic protection.

1.5Scope of study

Due to its wide range of the application of cathodic protection system and variations both in the design and installation, I decided to narrow it;

Sacrificial AnodeCathodicProtect (SACP) system will be used Using zinc as the anode of the system Applied in buried steel pipeline Designing the test rig at the site and sample preparation Analyze of the parameters; coating and type of anode that can be used forcathodic protection.

CHAPTER TWO:            LITERATURE REVIEW

2.1 Introduction

The first practical use of cathodic protection is generally credited to Sir Humphrey Davy in the 1820s. Davy’s advice was sought by the Royal Navy in investigating the corrosion of copper sheeting used for cladding the hulls of naval vessels. Davy found that he could preserve copper in sea water by the attachment of small quantities of iron or zinc; the copper became, as Davy put it, “cathodically protected”.

Later, in the early 1900's, when steel began to be used as a shipbuilding material in preference to naturally corrosion resistant iron on the grounds of economy and better mechanical properties, corrosion of ship's hull was identified as a serious problem. The area worst affected was at the after end of a vessel - an area of high wave turbulence and adjacent to the bronze propeller which creates a galvanic couple causing pitting of the adjacent steel. This problem was alleviated by the installation of zinc anodes around the stern frame and on the rudder - a practice that continues even today.

In the United Kingdom, where low-pressure thicker-walled cast-iron pipes were extensively used, very little cathodic protection system was applied until the early 1950s. The increasing use of cathodic protection has arisen from the success of the method used from 1952 onwards to protect about 1000 miles of wartime fuel-line network that had been laid between 1940 and 1944. The method is now well established.

The most rapid development of cathodic-protection systems was made in the United States of America to meet the requirements of the rapidly expanding oil and natural gas industry which wanted to benefit from the advantages of using thin-walled steel pipes for underground transmission. For that purpose the method was well established in the United States in 1945.

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DESIGN AND INSTALLATION OF CATHODIC PROTECTION SYSTEM USING ZINC ANODE



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