JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
ELECTRICAL ENGINEERING
CATHODIC PROTECTION SYSTEM AND IT’S
CONDITION MONITORING IN PETROLEUM
REFINERIES USING GSM BASED REMOTE
MONITORING UNIT RMU
1 MR.
PRASHANT KORADIA, 2 PROF. M N BHUSAVALWALA
1 Prashantkumar
Koradia ,ManageEssar Oil Ltd. ,Refinery Site, 39 KM, JamnagarOkha Highway , Vadinar - 361305
2 Prof. M. N. Bhusavalwala M.E.. Associate Professor, Head Of The Department ,S V
National Institute of Technology (SVNIT), Surat
Prashantkumar.Koradia@essar.com, mnb@eed.svnit.ac.in
ABSTRACT— Cathodic protection is technique used to protect steel materials against corrosion i.e.
underground vessels, pipelines, storage tank bottoms etc. buried underground or in sea water against corrosion.
The condition monitoring of cathodic Protection systems have received considerable attention in recent years
because corrosion may lead to spillage of oil and leakage of gases from storage tanks and Pipelines. Routine
measurements of CP level are required to comply with regulatory safety standards. In most of cases, the length
of pipelines for which CP level are to be measured are in lengths of kilometers. This paper includes the method
of condition monitoring of cathodic protection system in petroleum refinery using GSM based remote
monitoring unit (RMU).
Keyword:- Corrosion, Cathodic Protection, Condition Monitoring, GSM Based Remote Monitoring System,
Pipe To Soil Potential And Tank To Soil Potential.
I.
INTRODUCTION
In petrolieum refineries and petrochemical plants,
steel tanks and underground vessels for the storage
of crude oil and products as well as pipelines for
transferring the crude and products from crude
distrillation plant to storage area and then to product
storage & dispatch area are among the most parts of
the fixed plant facilities. Corrossion leads to not only
lossess of the metal and disconnection of the tank and
pipelines from the regular plant operation, but also
lossess of the product and severe environment
problems. Corrossion was a factor in 21.5% (28/128)
of all accidents in refineries reported to the MARS
database. Since 1980, 3 accidents account for the
majority of 60 deaths and 370 injuries arising from
these events (if BP Texas city -2005 is included). An
accident in Germany in 2006 estimated € 9.5 million
in environmental damage.
Cathodic Protection is a technique to reduce the
corrosion of a metal surface by making that surface
the cathode of that electrochemical cell.[1]
In 1971 Galvani noticed that when two metals having
different energy level or potential are coupled
together current will flow. The direction of positive
current flow will be from the metal with more
negative potential through the electrolyte to that
which is more positive. Corrosion will occur at the
point where positive current leaves the metal surface.
Corrosion is degradation of a metal by its chemical
combination with nonmetal such as oxygen sulphur
etc. [2]
Cathodic protection is an electrical method of
mitigating corrosion on structures that are exposed to
electrolytes such as soils and waters. Corrosion
control is achieved by artificially causing direct
current to flow from auxiliary anodes, through the
electrolyte (soil or water), and onto the structure to be
protected. It is a scientific method which combats
corrosion by use of the same law which causes the
corrosion process. It has widespread application on
underground pipelines, water storage tanks, lack and
gate dams, storage tanks bottom, Underground
storage tanks, pipelines under sea water etc. It has
been proven most effective corrosion control method.
[3]
II.
WHAT IS CORROSION ?
Corrosion is degradation of a metal by its chemical
combination with a non - metal such as oxygen,
sulphur etc. It is return of the metal to the form in
which it originally existed as an ore with complete
loss of its metallic properties. Naturally occurring
ores are oxides, sulfides or carbonates, and energy
must be expended in converting these ores to metal.
Corrosion is reverse process and it requires no
energy. Metals most easily obtained from their ores
requiring less energy in smelting least prone to
corrosion. Corrosion on underground pipeline if not
mitigated results in metal loss. One ampere of direct
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ELECTRICAL ENGINEERING
current discharging into the usual soil electrolyte can
remove approximately 9 Kg. of steel in one year. In
other words, corrosion is the wearing away of metals
due to a chemical reaction [4]
1.
Electrolytic corrosion.
Electrolytic corrossion is a result of direct current
from outside sources entering and then leaving a
particular metallic structure by way of electrolyte.
When current enters the structure, that part is usually
unaffected or is provided with some degree of
protection but when the current leaves the structure,
corrossion occurs. In underground work, this type of
corrossion is usually reffered as stray current
corrossion. This type of corrossion usually results
due to current entering the soil from sources of DC
like DC motors or DC powerhouse.
Fig : 1 Corrosion process.
Fig 4 : Stray Current Corrosion /Electrolytic
Corrosion.
Fig 2 : Chemical process of corrosion
2.
Galvanic corrossion.
All metals have specific relative electrical potential.
When metals of different electrical potential are in
contact in the presence of moisture, a low energy
electric current flows from the metal having the
higher position in the galvanic series. This is called
"galvanic action." Galvanic corrosion is a form of
electrochemical corrosion that occurs when two
dissimilar metals come together in the presence of an
electrolyte to form an electrical couple, known as a
galvanic couple. The more noble or cationic the
metal, the less likely it will corrode relative to the
other metal with which it is in contact. The more
active, or anodic, metal corrodes rapidly while the
more noble, or cathodic, metal is not damaged. The
difference in potential can arise from the coupling of
two dissimilar metals, variation of electrolytes, nonhomogeneity of the metal, or a combination of the
above.[6]
Fig 3 : Underground pipelines and seawater
corrosion.
III.
CORROSION MECHANISM
Electrochemistry contributes an understanding of the
mechanism that is basic to the corrosion of all
metallic objects. Metals in electrolytes get corroded
by the following two basic mechanisms [5]
1) Electrolytic corrosion.
2) Galvanic corrosion.
Fig 5 : Electrolytic Cell.
Current will be generated when two dissimilar metals
are electrically connected and immersed in an
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electrolyte. One of the metals will corrode. The path
of the current will be from the corroding metal,
through the electrolyte (soil) to the non-corroding
metal and then back through the connection
(conductor) between the two metals. The corroding
metal is the one where the current leaves to enter the
electrolyte and is called an anode. The metal that
receives the current is called the cathode.
The same metallic structure, when placed in an
electrolyte (e.g. soil) can develop differences in
potential as a result of metal grain composition,
milling imperfections, scratches, threads, etc., being
exposed. Those portions will usually be anodic to the
remainder of the surface and will corrode.
Fig 6 : Impression of local anodes and cathodes of
corrosion cells occuring on the same metal surface.
Corrosion can occur due to differences in the
electrolyte. These differences may be in the soil
resistivity, oxygen concentrations, moisture content
and various ion concentrations. The variations
produce current flow from one location, through the
electrolyte to another portion of the same metallic
structure.
It has been established that electric current can
generate corrosion, corrosion, in turn can generate
electric current. As indicated by these phenomena, it
is then possible to prevent corrosion by use of
electrical current. This is the basis for cathodic
protection. When direct current is applied with a
polarity which opposes the natural corrosion
mechanisms, and with sufficient magnitude to
polarize all the cathodic areas up to the open circuit
potential of the anodic areas, corrosion is arrested.
IV.
CATHODIC PROTECTION
Cathodic protection is a technique to reduce the
corrosion of a metal surface by making that surface
the cathode of that electrochemical cell. [1]
The concept of CP has been around for quite some
time. Marine vessels have used CP for almost 200
years The first recorded use of CP occurred in the
early 1800s. In 1824, Sir Humphry Davy was
consulted by the British Admiralty, which was
concerned about “the rapid decay of the copper
sheeting of His Majesty’s ships of war and the
uncertainty of the time of its duration.” Davy
proposed the attachment of a small piece of zinc to
nullify electrochemical action on the copper
sheathing. Davy also investigated this action using an
impressed current system [7].
Currently, CP is mandatory for underground, metallic
pipelines of hazardous gas and liquids [8], [9], and
for water storage tanks with a 250,000 gallon
capacity or greater [10]. Cathodic protection also is
recommended for underground piping systems
located within ten feet of steel reinforced concrete.
Galvanic corrosion will occur between the steel rebar
and the pipeline if the two systems are too close [10],
[11].
V.
TYPE OF CATHODIC PROTECTION
There are basically two methods of applying cathodic
protection.[12]
1) Sacrificial Anode Cathodic Protection.
2) Impressed Current Cathodic Protection
A)
Sacrificial Anode Cathodic Protection
Fig 8 : Sacrificial anode cathodic Protection
This is the simplest method of installation of cathodic
protection. As its name indicates, in this method, the
anodes used are of galvanic type with a higher
potential with respect to structure to be protected and
capable of self generating the DC current necessary
for the cathodic protection where the pipes/tanks are
cathodes. These anodes are mitigated as the time
passes and as they sacrifice themselves for protection
of cathode they are called sacrificial anodes.
Galvanic or sacrificial anodes are made in various
shapes and sizes using alloys of zinc, magnesium and
aluminum.
B)
Impressed Current Cathodic Protection
Fig 7 : Corrosion caused by dissimilar soils
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In this method, anodes are installed in the electrolyte
and are connected to the positive terminal of DC
power source while the structure to be protected is
connected to negative terminal of source. Direct
current is forced to flow from external source i.e.
transformer rectifier units. As this method uses
rectifier units it is referred as a rectifier type or
impressed current type cathodic protection. The flow
of this current is adjusted to overpower corrosion
current discharging from all anodic areas it provides
a complete protection.
Table 2 : CP readings in tabulated form
VII.
DIFFICULTIES IN CATHODIC PROTECTION
READINGS
Fig 9 : Impressed current cathodic protection
This method is widely used for pipelines and small
underground tanks to large petroleum tanks ranging
from 5 meter diameter to 80 meter diameter tanks. It
has an advantage that we can apply uniform current
of the same on piping and tanks and so through
protection occurs. Moreover it has a long life of 50
years after installation if maintained properly.
Table 1 : Comparison of GCP and ICCP
The following difficulties have been observed during
taking the CP readings:
1) Collection of periodic data is very essential as per
the defined frequency considering NACE standards.
Now as the pipe lines ranges in kilometers, collection
of data is a time consuming job. This also needs
travelling and vehicles etc to collect the data
frequently.
2) Collecting data at a periodic interval manually is
essentially reactive as the faults in the CP system can
go undected for at least a month at TRU’s and test
stations. This risks the pipeline being unprotected for
a long periods, accelerates corrosion and shortens the
life of structure.
3) As the pipelines passes through many geographical
locations, many CP control stations are difficult to
access and may need permission of land owner to
access the test stations.
4) At test stations with induced AC from power lines,
electric shocks can be generated from touch and step
potential voltages and high current level.
5) Highly skilled engineers/technicians are needed for
the data collection. There are chances of
manipulation of data which are actually not taken by
the engineer/technician from engineer/technician
side. As the data are taken manually the accuracy of
the data is not up to the desired accuracy.
6) This hard data is again needed to be converted into
soft copy in form of excel sheet or word format as per
the requirement and in this case also there are
chances of mistakes from the data operator.
7) There are chances of insect bites, animal attacks,
honeybee attacks etc near the test stations.
VIII.
REMOTE MONITORING OF CP SYSTEM
USING GSM
BASED REMOTE MONITORING DATA
LOGGERS
The comparison of sacrificial anode cathodic
protection system and impressed current cathodic
protection can be shown as above.
VI.
CATHODIC PROTECTION READINGS
The frequency of cathodic protection readings should
be weekly. The value of PSP or TSP should be noted
fortnightly from each test station unit. The tabulated
form of the same is shown below.[1]
Fig 10 : Front view of one of RMU
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of data from about 25 to 50 RMU’s in the field into
the central computers kept at the control room.
Fig 10B : lower view of one of RMU
The present trend in remote monitoring of the
cathodic protection has turned to GSM based remote
monitoring units (RMU) data logger instead of
manual data collection or data collection by old type
of data loggers without screen and memories.
GSM based remote monitoring units data logger are
highly accurate, compact, low powered, low cost,
microcontroller based units with built in GSM
modem which enables continuous centralized
monitoring of CP TR parameters at the central station
wherever required. Moreover they have the facilities
of configuration of mobile numbers. The unit
provides data by means of SMS sent to the
programmed mobile numbers.
Fig 11 : Data in graphical form
The RMU enables easy and wireless centralized
monitoring of TR parameters like AC supply voltage
and current, DC output voltage, DC output current,
reference potential (PSP), AC supply voltage. Also
this RTU generates alarm conditions like pipe or tank
overprotection, pipeline or tank underprotection,
reference fail, TR door open especially as theft
monitoring.
At remote end the data could be received using a
GSM interface module connected to the computers
installed with the CP software provided by the
manufacturer of this RMU. This software displays
the acquired data of TR unit in analytical and
graphical formats and stores the data in the standard
databases like MS ASCESS which is used for
generating reports for further analysis of structure
under protection. The datas can be exported into MS
EXCEL spreadsheet as well as tables and graphs. The
interface modules are designed to direct downloading
Fig 12 : Laptop software screen for setup
The data logging and broadcast schedule may be
fully programmed from 1 reading in 5 minutes to 1
reading per day as per the requirement of user and
this data is also directly received in the mobile
phones of maintenance personnel for the reactive
action against the protection of pipeline.
Apart of sending the TR data to the remote stations,
these RMU also logs the data in their volatile
memory with accurate day-date-time stamp for each
reading at the programmed logging interval and thus
they also work as local data loggers. Also they have
small 2 line LCD display to verify the datas and
ensure that the input is connected properly and logger
is receiving signals from the field. The RMU can
store about 20-000 to 30-000 date readings which can
be downloaded through laptop or computer using a
RS 232 port. The stored data can be retained for 10
years without any external powers. These RMU also
has commands for starting and stopping the unit
current interruption of TR units wherever desired.
This gives us flexibility of making the TRU ON/OFF
from the control station whever required.
The RMU also have local key pads through which set
parameters for the alarm conditions can be feed or
changed as per the requirement. The real time clock
setting with day date and year can be done along with
password protections so that the exact time stamping
of data or alarms can be stored.
The most important feature of these RMU is that they
are housed in a compact and sturdy non corroding
enclosure inside the existing TRU with direct or
channel mounting and dimensions ranging from
200mm X 200mm X 150 mm to less compact size of
180 mm X 150 mm X 100 mm. These RMU are
micro processor based, they can work on any supplies
like 230V + 20 % AC, 20 to 120 V DC, 12V DC etc
and can work in the temperature range from -10
degree celsius to 75 degree celsius. These RMU can
be feed directly from the power fed to TRU.
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The costs of this type of RMUs range in between
25,000 to 75,000 rupees. It has a payback period of
about 3-5 years if data required monthly readings of
TRU and test stations.
IX.
LIMITATIONS OF RMU :
Along with all these there are some drawbacks of
RMU’s as stated below:
1) The RMU cannot do remote monitoring at the
spaces where there are weak or no signals of GSM.
2) The cost of GSM SIM card is one time amount to
be paid to GSM network operator. Also monthly
amount to operate this card is to be paid to GSM
network operating from which SIM is purchased as a
billing amount each month.
X.
LIST OF ABBREVATIONS :

CP = Cathodic Protection.

GSM = Global System for Mobile
Communications.

RMU = Remote monitoring unit.

CM = Condition monitoring.

TRU = Transformer Rectifier unit.

PSP = Pipe to Soil Potential.

TSP = Tank to soil potential.

GCP = Galvanic cathodic protection.

ICCP = Impressed current Cathodic
Protection.

SIM = Subscriber identity Module.
XI.
CONCLUSION
Cathodic protection is one of the most economical
methods of preventing corrosion. This method needs
continuous monitoring of data as per the predefined
frequency. Remote monitoring of cathodic protection
on buried metal pipelines, underground vessels and
tankage base was one of the significant technical
challenges for petroleum industries.
The development of low power consumption
microprocessor based electronics with affordable
communication system has helped to overcome these
challenges. Petroleum and gas industries are now
adopting the remote monitoring system using GSM
based remote monitoring units for cathodic protection
TRU’s and CP test stations. This has enabled better
utilization of human reducing the shock hazards. By
identifying and reporting the problems as they occur,
remote monitoring units ensure continuous and
effective cathodic protection and hence increase the
life of structure to be protected.
REFERENCES
[1]
NACE SP0169:2007 - Control of External
Corrosion on Underground or Submerged Metallic
Piping Systems.
[2]
The corrosion and cathodic protection.
[Online].
Available:
http://www.generalcorrosioncorp.com/TechInfoSubP
ages/GCC_CPTraining2.pdf
[3]
Cathodic protection anode selection, Public
work technical bulletin 420-49-27, 15th June 200.
[Online].
Available:
http://www.wbdg.org/ccb/ARMYCOE/PWTB/pwtb_
420_49_37.pdf
[4]
Roberge, Pierre R, Handbook of Corrosion
Engineering 1999.
[5]
Cathodic Protection [Online]. Available:
cpcorrosion.blogspot.com/2009/08/corrosionmechanism.html
[6]
Matthew
Stuart,
“Dissimilar
metal
corrosion”
[Online].
Available:
http://www.pdhonline.org/courses/s118/s118.htm
[7]
Sir H. Davy, “On the corrosion of copper
sheeting by seawater, and on methods of preventing
this effect, and on their application to ships of war
and other ships,” Proc. R. Soc. Lond., vol. 114, no.
1824, pp. 151–246 and vol. 115, no. 1825, pp. 328–
346.
[8]
Department of Transportation, Washington,
DC, Transportation of Natural Gas and other Gas by
Pipeline. 49 CFR, Part 192.
[9]
Department of Transportation, Washington,
DC, Transportation of Hazardous Liquids by
Pipeline, 49 CFR, Part 195.
[10]
Department of the Army, Washington DC,
Maintenance of Mechanical and Electrical Equipment
at Command, Control, Communications, Computers,
Intelligence, Surveillance, and Reconnaissance
(C4ISR) Facilities, TM 5-692-2, Chapter 31, Apr. 15,
2001.
[11]
Department of the Army, Washington DC,
Electrical Design, Cathodic Protection,
[12]
J. Paul Gayer, An Introduction to cathodic
protection, El Macero CA, 2009.
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