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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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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 0
C and cooled in water bath at different temperatures 40, 50, 60 0
C.
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 0
C.
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.
