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Preface:

Corrosion is chemical degradation under the corrosive environment which leads the flaws and

imperfection in the usefulness of engineering materials. So, corrosion is an undesired materials

property. To mitigate the adverse effects of corrosion, national association of corrosion

engineering (NACE) has introduced many reforms and precautions in order to minimize the

hazardous caused by corrosion. The commonly used corrosion protecting activities in industries

including SNGPL are simple or multilayer coatings and cathodic protection (CP) by using

sacrificial anode. These activities are economical feasible and ensure the services delivery

without any damage to the customers with the view of their satisfactions.

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Table of Contents 1-Introduction: ................................................................................................................................ 5

1.1-Problem & Purpose:.............................................................................................................. 5

1.2-Scope: ................................................................................................................................... 5

1.3-Limitations: ........................................................................................................................... 5

Section I .......................................................................................................................................... 5

1-Overview: .................................................................................................................................... 5

Section II ......................................................................................................................................... 7

2-Corrosion mitigation: ............................................................................................................... 7

2.1- Coating system: ................................................................................................................... 7

2.2-Cathodic Protection: ............................................................................................................. 7

2. 2.1-Transformer Rectifier (TR): ............................................................................................. 8

2. 2.2-Pipe line current mapper (PCM):...................................................................................... 8

Section III........................................................................................................................................ 9

3-Coating inspection work .............................................................................................................. 9

3.1-Primer strength test: .............................................................................................................. 9

3.2-Softening point test: ............................................................................................................ 10

3.3-Density test: ........................................................................................................................ 10

3.4-Automatic high temperature oven: ..................................................................................... 10

3.5-Volatile matter determination test: ..................................................................................... 11

3.6-Sieve analysis: .................................................................................................................... 11

3.7-Ultimate tensile strength machine: ..................................................................................... 12

3.8-Preparation of Thermo glass: .............................................................................................. 13

3.9-Penetrometer: ...................................................................................................................... 13

3.10-Automated Rockwell test: ................................................................................................ 14

3.11-Flame photometer: ............................................................................................................ 14

4-Conclusion: ................................................................................................................................ 15

5- Appendix: ................................................................................................................................. 16

6-References: ................................................................................................................................ 17

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List of Figures:

Figure 1: Pipe line corrosion ......................................................................................................... 05

Figure 2: Cathodic Protection ....................................................................................................... 07

Figure 3: Transformer Rectifier TR .............................................................................................. 08

Figure 4: Pipe line current mapper (PCM) ................................................................................... 09

Figure 5: primer ............................................................................................................................ 10

Figure 6: Softening point machine ................................................................................................ 10

Figure 7: Automatic high temperature oven ................................................................................. 11

Figure 8: Volatile determination oven .......................................................................................... 11

Figure 9: Seiving ........................................................................................................................... 12

Figure 10: Universal testing machine UTM ................................................................................. 13

Figure 11: Preparation of Thermo glass........................................................................................ 13

Figure 12: Penetrometer ................................................................................................................ 14

Figure 13: Superficial Rockwell ................................................................................................... 14

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Abstract:

This experimental documents comprises the effects and mitigations of the chemical corrosion of

gas pipe line which is consider the assets of sui northen gas pipe lines limited SNGPL. It is very

imperative to take expedient steps to encounter the adverse effect of corrosion successfully.

Numbers of techniques such as protective coating system or cathodic protection (CP) along with

sacrificial anode have been developed to abort the corrosion cycle.

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1-Introduction:

1.1-Problem & Purpose:

Corrosion is basically the destruction of engineering materials mainly metal gas pipe lines which

leads the materials towards limited values in their applicability. So, we have to face many

problems associated with corrosion. That’s why it is very crucial to elect the suitable methods

which can efficiently abort the development of the corrosion cell in gas pipe lines. The selection

of corrosion protecting activity depends upon the nature of installing materials and geographical

and physical location.

1.2-Scope:

With the help of this experimental document, it can be deduced that in what ways we might be

able to harness the adverse effects caused by corrosion. Every method has its own applications

and limitations. So, chosen proper and perfect activity will assist in the protection of gas pipe

line from toxic environment interactions.

1.3-Limitations:

Multilayer coating system is efficient in order to enhance the life of pipe lines but its high

cost distract its usefulness

Soil stresses and soil contaminations should be successfully encountered to avoid the

degradation of applied coating over pipe lines

Selection of suitable corrosion protecting method vary as processing variables like type

of material, location, installation method or cost

Experience and expert instructors are required to manage the operating system

Section I

1-Overview:

One general definition of corrosion is the degradation of a material through environmental

interaction. This definition encompasses all materials, both naturally occurring

and man-made and includes plastics, ceramics, and metals. This book focuses on the

corrosion of metals, with emphasis on corrosion of carbon and low-alloy steels used

in underground pipelines. This definition of corrosion begs the question; why do metals corrode?

The answer lies in the field of thermodynamics, which tells whether a

process such as corrosion will occur. A second logical question is what is the rate

of corrosion or how long will a pipeline last? Corrosion kinetics can help provide an

answer to this question.

A significant amount of energy is put into a metal when it is extracted from its

ores, placing it in a high-energy state. These ores are typically oxides of the metal such

as hematite (Fe2O3) for steel or bauxite (Al2O3·H2O) for aluminum. One principle of

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thermodynamics is that a material always seeks the lowest energy state. In other words,

most metals are thermodynamically unstable and will tend to seek a lower energy state,

which is an oxide or some other compound. The process by which metals convert to the

lower-energy oxides is called corrosion.

Figure 1: Pipe line corrosion

Corrosion of most common engineering materials at near-ambient temperatures occurs in

aqueous (water-containing) environments and is electrochemical in nature. The

aqueous environment is also referred to as the electrolyte and, in the case of underground

corrosion, is moist soil. The corrosion process involves the removal of electrons (oxidation) of

the metal [Equation (1)] and the consumption of those electrons by

some other reduction reaction, such as oxygen or water reduction

Fe Fe ++

+ 2e-

O2 + 2H2O + 4e

- 4OH−

2H2O + 2e- H2 + 2OH

-

The oxidation reaction is commonly called the anodic reaction and the reduction

reaction is called the cathodic reaction. Both electrochemical reactions are necessary for

corrosion to occur. The oxidation reaction causes the actual metal loss but the reduction

reaction must be present to consume the electrons liberated by the oxidation reaction,

maintaining charge neutrality. Otherwise, a large negative charge would rapidly develop

between the metal and the electrolyte and the corrosion process would cease.

The oxidation and reduction reactions are sometimes referred to as half-cell reactions

and can occur locally (at the same site on the metal) or can be physically separated.

When the electrochemical reactions are physically separated, the process is referred to

as a differential corrosion cell. There are four necessary components of differential cell.

Anode

Cathode

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Metallic path for the electric connection between cathode and anode

A conductive electrolyte which is moist soil in gas pipe line under ground

There are different ways in order to abort the corrosion in gas pipe line system.

Coating

Cathodic protection

Passivation

First are commonly applied in gas pipe line industries like in SNGPL.

Section II

2-Corrosion mitigation:

The principal methods for mitigating corrosion on underground pipelines are coatings

and cathodic protection (CP). Although each will be treated in greater detail in the

following chapters, these two methods are briefly described here.

2.1- Coating system:

Coatings normally are intended to form a continuous film of an electrically insulating

material over the metallic surface to be protected. The function of such a coating is to

isolate the metal from direct contact with the surrounding electrolyte (preventing the

electrolyte from contacting the metal) and to interpose such a high electrical resistance

that the electrochemical reactions cannot readily occur. In reality, all coatings, regardless

of overall quality, contain holes, referred to as holidays that are formed during application, or

during transport or installation of mill-coated pipe. Holidays in coatings also

develop in service as a result of degradation of the coating, soil stresses, or movement of

the pipe in the ground. Degradation of the coating in service also can lead to disbonding

from the pipe surface, further exposing metal to the underground environment. The primary

function of a coating on a cathodically protected pipe is to reduce the surface area of

exposed metal on the pipeline, thereby reducing the current necessary to cathodically

protect the metal.

2.2-Cathodic Protection:

One definition of CP is a technique to reduce the corrosion rate of a metal surface

by making it the cathode of an electrochemical cell. This is accomplished by shifting the

potential of the metal in the negative direction by the use of an external power source

(referred to as impressed current CP) or by utilizing a sacrificial anode. In the case of an

impressed current system, a current is impressed on the structure by means of a power

supply, referred to as a rectifier, and an anode buried in the ground. In the case of a

sacrificial anode system, the galvanic relationship between a sacrificial anode material,

such as zinc or magnesium, and the pipe steel is used to supply the required CP current. [1]

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Figure 2: Cathodic Protection

2. 2.1-Transformer Rectifier (TR):

The discontinuity of the coating materials is judge by the transformer rectifier (TR). In this

context, AC current is step down from 220 volts to 50 volts and this AC current is transformed

into DC current. Both single-phase and three-phase units are in common use.

Figure 3: Transformer Rectifier TR

2. 2.2-Pipe line current mapper (PCM):

The hand held receiver unit is used to locate the pipeline, even in heavily congested areas such as

conduits, and then provides the operator with a measurement of depth current strength and signal

direction applied by the transmitter to quickly pinpoint corrosion related problems. The receiver

makes the required calculations and instantaneously displays the results. This provides the

operator with an improved method that accurately troubleshoots the CP system by pinpointing

metallic contacts and locating areas of coating defects. [2]

Figure 4: Pipe line current mapper (PCM)

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Section III

3-Coating inspection work

3.1-Primer strength test:

Coal tar is heated at 260 0C and cooled in water bath at different temperatures 40, 50, 60

0C.

Then the peeling is applied to check the stability of primer over attached material. The layer of

primer which is peeled must be able to retain during the test when peeling is carried out. If it is

stable without damage, the primer is passed for use over pipes as coating materials.

Primer is also heated in oven at high temperature for 72 hours and again peeling is done after

cooling in water bath at 40, 50, 60 0C.

Coal tar enamel 260°C

Water bath 40, 50, 60°C

Peel

Oven 72 hours

Water bath 40, 50, 60 °C

Peel

Primer applied on metal sheet is shown in below figure.

Figure 5: Primer

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3.2-Softening point test:

This advanced microprocessor controlled automatic tester is used to determine the softening

point of bitumen using, as heating fluid, water or glycerol. The softening point is taken by two

light barriers suitably positioned and the temperature measured by a sensor placed in a middle

position. During operation a magnetic stirrer with adjustable speed assures temperature

uniformity in the vessel. The temperature gradient is strictly maintained throughout the test by

the electronic system conforming to the standards.

Temperature 5 to 200°C

Heating rate 5°C /minute

Depth of pin 5-12mm

Weight of sample 100g

Figure 6: Softening point machine

3.3-Density test:

The sample is placed in the water. Density is determined according to the Archimedes Principle

which should be beween 1.4-1.6g/cm3.

3.4-Automatic high temperature oven:

Used for bond/peel test for C.T and oil based enamel. Temperature is around 400°C at which

material is heated and then cooled at 70°C where peel/bond checking is done.

The percentage of carbon present inside sample is checked through this test present is ash.

Temperature 700-760°C

Time 3hours

After every 1 hour weight if sample is checked.

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Figure 7: Automatic high temperature oven

3.5-Volatile matter determination test:

Moisture content present inside sample is checked in this test. Heating is done in oven at 20-

200°C. Our set point is between 105-110°C. Time is almost 3 hours.

Figure 8: Volatile determination oven

3.6-Sieve analysis:

A sieve analysis (or gradation test) is a practice or procedure used (commonly used in civil

engineering) to assess the particle size distribution (also called gradation) of a granular material.

The size distribution is often of critical importance to the way the material performs in use. A

sieve analysis can be performed on any type of non-organic or organic granular materials

including sands, crushed rock, clays, granite, feldspars, coal, soil, a wide range of manufactured

powders, grain and seeds, down to a minimum size depending on the exact method. [3]

For Hard coke

Mesh size 10 mm

Passage (undersize) 85%

Mesh size 12 mm

Passage (undersize) 100%

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For Breeze coke

Mesh size 20 mm

Passage (undersize) 98%

Mesh size 10 mm

Passage (undersize) 80%

Figure 9: Sieve analysis

3.7-Ultimate tensile strength machine:

Tension and compression test are performed on fiberglass to determine its strength.

Thickness of film = 13 mils

Fiberglass is clamped in the chucks and load is applied.

13 pounds/227 Newton load is desirable at which material is passed for further

processing.

ASTM 900 standard is followed.

Figure 10: Universal testing machine UTM

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3.8-Preparation of Thermo glass:

Pultration technique is used to make strong, lightweight composite material in plant to protect

the pipe from corrosion. Fiberglass over which the melted coal tar enamel is coated is pulled

through continuous roller method. At end they are cut to desired length and then rolled.

Length = 21 inch width = 3 inch

Figure 11: Preparation of Thermo glass

1) fiber glass

2) roller for pushing fiber glass inside melted C.T.E

3) melted C.T.E

4) fiber glass coated with C.T.E coming out of furnace

5) cooling time is given and powder is poured over the fiber glass coated with C.T.E

6) rollers pushing the fiber glass coated with C.T.E

7) fiberglass coated with C.T.E cutting

3.9-Penetrometer:

For testing of penetrative of asphalt and coal tar enamel (CTE). BS 4147, 4146

With ASTM 36 D standard

Max. load / weight 100 gm

Penetrating time 0 to 999 min and 59 sec

Range of penetration is 0.1 mm to 58 mm

Accuracy 0.02 mm

Figure 12: Penetrometer

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3.10-Automated Rockwell test:

This is used for measuring of hardness by testing comparative depth of two carefully controlled

indentations one superimposed on other. For thin section, normally superficial scale is used. [4]

Figure 13: Superficial Rockwell

3.11-Flame photometer:

This is standard operating procedure in order to check the purity of potassium in a solution.

A photoelectric flame photometer is a device used in inorganic chemical analysis to determine

the concentration of certain metal ions, among them sodium, potassium, lithium,

and calcium. The operating procedure is

It must show 000 reading on digit screen

Make ppm solution of different concentrations like 20, 40 and 60 ppm

Take 2 ml of It stock solution with 98 ml of deionize water to make 20 ppm sol

Similarly 4 ml stock solution with 96 ml of ionize water to make 40 ppm sol

Similarly 6 ml stock solution with 94 ml of ionize water to make 60 ppm sol

Take emissivity reading from flame meter and draw calibration graph

Take 2.59 ml KNO3 and dissolve in 1000 ml of deionize water, 1000 ppm sol is ready to

use

Test this sol and draw its emissivity reading where it cut reference line from this point

draw a straight line on x-axis to get result

Result = (Reading on x-axis / sample sol n ppm) * 100 = % purity of potassium

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4-Conclusion:

The whole discussion reported in this document reveals that corrosion is a serious problem and

conducive steps need to be taken to mitigate the adverse effect of corrosion. So, to avoid the

destruction of gas pipe lines, different techniques have been developed by the national

association of corrosion engineering (NACE). Coating system and cathodic protection (Cp) with

protective or sacrificial anode are commonly used to avoid the chemical degradation of pile

lines. Before installing the protection methods, different test are used to check the service

applications of applied techniques and proper modification are to be carried out to improve the

efficiency of applied technique to reduce the chances of environmental interaction of pipe lines

system.

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5- Appendix:

1. Cathodic protection (CP) pg. # 5

2. Transformer rectifier (TR) pg. # 6

3. Pipe line current mapper (PCM) pg. # 6

4. Primer pg. # 7

5. Programmable Oven pg. # 8

6. Sieving pg. # 9

7. UTM pg. # 10

8. Penetrometer pg. # 11

9. Thermo glass pg. # 11

10. Flame photometer pg. # 12

11. Automated Rockwell pg. # 12

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6-References:

[1]: Peabody’s control of pipeline corrosion edition 2, chapter 1

[2]: http://zebu.uoregon.edu/text/cathodic protection

[3]: http://en.wikipedia.org/wiki/Strength_of_materials

[4]: http://www.jenway.com