Pipelines Division of IndianOil : Assets
™ IOCL Pipeline network having total length of more
then 10541 km, comprising pipelines of sizes
ranging from 8” to 48” dia and 72 MMTPA (1.44
Million bpd) capacity
™ 72 installations across India
™ 3 Single Point Mooring systems
™ 63 bulk crude storage tanks (approx. total capacity
25 Million bbl)
™ Dedicated Telecom (with over 6,500 km OFC),
SCADA system
OPERATING PIPELINES (As on
31.03.2010)
Length
(KM)
Capacity
(MMTPA)
Crude Oil pipeline
6175
34.86
Product Pipeline
4366
40.40
Total
10,541
75.26
PIPELINES
Crude Oil pipeline
Product Pipeline
- LNG pipeline (Dadri- Panipat)
R
Product pipeline (under
Construction/Proposed)
LPG Pipeline ( Panipat Jalandhar)
IOCL PIPELINES
•
IOCL pipelines, those commissioned in 60’s have
already served for more than 50 years and still being
operated at Max. allowable operated pressure &
achieving the yearly throughput target.
•
Implementation of effective health monitoring &
corrosion prevention programme has helped in
achieving the safe, economical
& reliable
operations of pipelines.
Why do pipelines fail?
• Causes of pipelines failures
– Third party damage
– Corrosion (Internal/External)
– Construction/Material defect
– Natural Calamities/Ground movement
– Other causes (operational error)
Failures in IOCL’s Operating Pipelines
50
%
P/L FAILURES
40
30
20
10
0
Mech/Material Corrosion
Third
failures
failures party/Pilferages
failures
Others
Integrity Management of Pipelines
Spillage of oil
&
Fire hazard
Environmental
damage
near leak spot
Pipeline
Failure:
Consequences
Legal Issues,
Financial Loss
Interruption
in petroleum
supply
Integrity Management Practices in Indian Oil
Prevention Against Corrosion : Approach
™
Identification of possible causes of corrosion
™
Evaluating approaches / methods to deal with corrosion
™
Selecting Corrosion Monitoring & Mitigation
comprising CP and diverse coating solutions
™
Dealing with challenges in achieving effective corrosion
mitigation measures
™
Instituting an effective corrosion mitigation programme and
experience sharing
methods
Identification of possible causes of Pipeline corrosion.
Major Causes of Pipeline External Corrosion :z
Poor/defective Coatings.
z
Inadequate Cathodic Protection (CP).
z
Coating defects combination with inadequate CP.
z
Interference due to external agencies.
z
Stress & Bacterial corrosion.
Major Causes of Internal Corrosion :z
Corrosive nature of fluid transported through pipeline.
z
Erosion – Corrosion.
z
Localized Chemical attack/bacterial corrosion.
Integrity Management Practices in Indian Oil
Thrust
Areas
Monitoring
Monitoring
Pipeline
Integrity
Cathodic
Protection
Monitoring
Coating
Selecting Corrosion Mitigation methods.
Mitigation Of External Corrosion in Pipelines:
i) Protective Coating
• Effective coating/painting on metal structures is the
best and most economical way of corrosion control.
• For cross-country pipeline, the primary protection is
coating .
• Coating isolates the metal surface from contact with
the surrounding & avoid corrosion.
Pipeline Coatings
Plant Coating
– Coal Tar Enamel Coating
– 3 Layer Polyethylene Coating
– Fusion Bonded Epoxy
– Dual Fusion Bonded Epoxy
Field Coating/Refurbishment Coating
– Coal Tar Enamel Coating
– Hot Applied Coal Tar Enamel Tape
– Cold Applied Tape
– Polyurethanes coating
– Epoxy Coatings
SHOT BLASTING UNIT
SHOT BLASTED PIPE
INDUCTION HEATING
EPOXY POWDER SPRAY CHAMBER
EPOXY POWDER BEING SPRAYED
SIDE EXTRUSION OF ADHESIVE & PE LAYERS
THREE LAYING COATING PLANT
SCHEMATIC
Mitigation Of External Corrosion in Pipelines
ii)
Cathodic Protection (CP)
• CP is a viable tool for Corrosion prevention.
• Corrosion is an electrochemical phenomenon,
therefore effectively mitigated by altering the
electrochemical condition.
• Due to potential difference at various points on
pipelines current flows. The points where current
leaves the pipeline and enters electrolyte, corrosion
takes place.
• The points where current flows from electrolyte to
pipe, called cathode, no corrosion takes place and
pipe is protected.
PRINCIPLE OF CATHODIC PROTECTION SYSTEM
ANODIC
CATHODIC
CURRENT FLOW
In a buried cathodically unprotected pipeline, due to Various
conditions like difference in soil resistivity, Differential
aeration, etc., Cathodic and anodic regions are formed,
which will set up a corrosion cell (short cell or long cell)
among themselves.
Anodic regions will discharge current to the soil and hence,
would corrode. Current thus flowing is termed as corrosion
Current.
Selecting Corrosion Mitigation methods.
Mitigation Of External Corrosion in Pipelines:
ii)
Cathodic Protection (CP)
• In cathodic protection dc current is forced to flow from
external source to metallic structures (reversing natural
corrosion current). When current density is adjusted
properly it will over power corrosion current
discharging from anodic areas.
• There will not be current flow from pipe surface to soil
(electrolyte) and hence corrosion will be stopped.
• If all points on pipeline are made to collect current from
electrolyte, no corrosion will take place because entire
pipeline will become cathode. This is what cathodic
protection (C P) does.
BASIC THEORY OF CATHODIC PROTECTION
• CH-3
CH-3
Selecting Corrosion Mitigation methods.
Mitigation Of External Corrosion in Pipelines:
ii) Cathodic Protection (CP)
• Pipe to soil potential (PSP) measurements are carried out to know
the extent to which the corrosion to the pipeline has taken place.
• The minimum PSP shall be more negative than (-) 0.85v with
respect to copper –copper sulphate electrode.
• In areas where anerobic bacteria are active, minimum psp shall be
more negative than(-) 0.95v instead of (-) 0.85v.
• Over protection of pipeline to be avoided by ensuring that
polarisation potential (instant off potential ) is below –1.20 volts
wrt cu-cuso4 half cell.
TYPES OF CP SYSTEMS
• SACRIFICIAL (OR GALVANIC) ANODE CP
SYSTEM
• IMPRESSED CURRENT CP SYSTEM
SACRIFICIAL SYSTEM
Cathodic Protection with Galvanic Anodes
•
•
•
•
•
The corrosion cell resulting from contact of dissimilar metals, one
metal is active (negative) with respect to the other and corrodes. In
CP with galvanic anodes, this effect is taken advantage of by
purposely establishing a dissimilar metal cell strong enough to
counteract corrosion cells normally existing on pipelines..
Under normal circumstances, the current available from galvanic
anodes is limited. For this reason, CP by galvanic anodes normally
is used where the current required for protection is small
Similarly, the driving voltage existing between pipe steel and
galvanic anode metals is limited. Therefore, the contact resistance
between the anodes and the earth must be low for the anodes to
discharge a useful amount of current.
This means that, for normal installations, galvanic anodes are
used in low-resistivity soils.
There are also instances where galvanic anodes are placed at
specific points on a pipeline (often termed hot spots) and maybe
expected to protect only a few feet of pipe, especially where the
line is bare.
IMPRESSED CURRENT SYSTEM
CATHODIC PROTECTION WITH IMPRESSED
CURRENT
• To be free of the limited driving voltage associated with
galvanic anodes, current from some outside power
source may be impressed on the pipeline by using a
ground bed and a power source.
• The most common power source is the rectifier. This
device converts alternating current (AC) electric power to
low-voltage direct current (DC) power. Rectifiers usually
are provided with the means for varying the DC output
voltage in manual and auto mode so that we can made
small increments over a reasonably wide range.
Cathodic Protection Station
Effect of the Coating on Cathodic Protection
Effect of the Coating on Cathodic Protection
•
•
•
•
•
The engineer also must be able to estimate the rate of degradation of the
coating so that the CP system can be designed to protect the pipeline as the
coating degrades.
Very long lengths of pipeline can be protected with a single CP system. For
example, it is frequently possible to protect over 50 miles of cross-country
pipeline from one location, if the pipeline has a large-diameter and is well
coated.
it is easier to protect long lengths of large-diameter pipe than of small-diameter
pipe from as ingle CP installation.
Current flow at any location on the pipe is inversely proportionally to the total
resistance of the system at that location, based on Ohm’s law. Once the current
enters the mass of the earth from a ground bed, it is in a very low resistance
conductor and theoretically will travel great distances if there is a suitable return
conductor. In pipeline work, the pipe itself is the return conductor..
For a given wall thickness, large-diameter pipe has a lower resistance than
small-diameter pipe because the former has a larger cross-sectional area and
the resistance of a conductor is inversely proportional to the cross-sectional
area.
GROUND BED
MULTITECHNIQUE PIPELINE COROSSION MONITORING
Category
Example
First Pass
Reading of CP test station
Second Pass
Close Interval Potential survey
“Hot spot survey”
Third Pass
CAT, DCVG, Soil Resistivity survey
Final Pass
Selective excavation , ultrasonic and
magnetic flux measurement,
Microbiological testing
Increasing detail, information and confidence in characterizing
corrosion damage is obtained by moving down( as detailed above)
and across this matrix i.e. by utilizing an increasing number of
technique.
ON/OFF POTENTIAL MEASUREMENT
700
750
Potential
(mV/CSE)
Polarization
Decay
800
Instant – off
Potential
850
IR
Drop
900
‘ON’ Potential
950
CP System
Switched OFF
1000
1050
To
Pipelines Division
NOIDA
Time
Tx
6
Potential Plot
UCu/CuSO4
18,0 μA/m 2
(V)
20 k Ω.m
2
16,2 μA/m 2
22 k Ω.m
15,9 μA/m 2
2
25 k Ω.m
2
-1,40
-1,30
-1,20
-1,10
-1,00
-0,90
-0,80
-0,70
1,16A
a
-0,60
0,35A
0,30A
0,22A
0,00A
R LA R
8,980 8,360
R
7,280
R
5,360
I (1,5 Ohm)
0,000
-0,50
8,850
km
3
4
8
7
7
0
1
0
8
0
0
0
0
0
0
6
0
0
6
6
1 1.33
1 1.63
1 1.81
1 6.63
1 9.63
2 6.25
2 9.49
3 2.50
3 3.11
3 6.10
3 7.90
4 3.80
4 5.80
4 7.76
5 0.39
5 2.64
5 4.39
5 7.44
5 9.01
6 5.15
4 .9 2 6
2 .0 1 5
0 .2 5 0
PS P V O L T (-)
PSP profile
2.05
1.95
1.85
1.75
1.65
1.55
1.45
1.35
1.25
1.15
1.05
0.95
0.85
0.75
0.65
0.55
Qtr:2nd (April.-June 2006)
OFF PONTIAL
DATUM
PPMAX
CHAINAGE (KM)
Latest Trend
•
•
•
The latest trend is to evaluate the effectiveness of Cathodic
Protection on the basis of Instant “off” pipe to soil potential.
Measuring probes if installed along ROW at all test station will
provide facilities for measuring absolute potential , Instant off
potential and data for study the mitigation of the interference
problem. Holiday in the coating can be simulated by the way of
steel electrode of various area & size , connected to pipe via
TLP.
The measuring probe in combination with Computerized Test
Station can provide data base for further analysis of the
effectiveness of the Cathodic Protection . Recorder installed in
the Computerized test station and stored data can be retrieved
for further analysis/ remedial measures. Self contained
measurement and as well as registration of corrosion effect
over a period of time is stored in the recorder
Measuring Probe
•
•
•
•
Measuring probes consist of a permanent reference
electrode and auxiliary metal electrode simulating damaged
coating having various area sizes. Metal of the auxiliary
electrode are same as that of pipe.
Surface area of auxiliary electrode may 10 or 100 cm2
,thickness around 3mm and dia from 36 mm to 113 mm.
In case of measuring probe 110 or 200 , one of the coupon
either 10 or 100 cm2 is connected to pipeline through test
lead point with an isolating switch . Normally this switch is
kept “On” position . Other coupon is left unconnected . The
former simulates a holiday in pipeline coating and later
simulate bare pipe in the soil without Cathodic protection.
The resistance between coupon to pipe is measured using
once in a six month.
Typical Diagram of Measuring Probe
3 X 4 MM2 CABLE
AREA 10 OR 100 CM2
AREA 100 CM2
CU- CUSO4 ELECTRODE
Application of Measuring Probe
•
•
Probes are used to determine the corrosion of buried steel
pipelines and tanks including stray current area. The places
where stray current influences are expected , or
interference of CP connected to foreign pipelines are
existing, or the soil strata consisting of hard rock of very
high resistively , or where equalizing current flow through
soil due to vastly different PSP of two adjacent structures,
the over the ground PSP would not give a correct
potential of pipeline under test. In such circumstances , the
Measuring Probes could be put to use for obtaining the
correct potential of the pipe.
Without requirement of special measuring tool or
instrument, measuring probes are helpful in accurate and
faster check of the state and effectiveness of Cathodic
protection
Application of Measuring Probes
Probes are to be placed permanently in locations with
complicated
conditions from the point of view of following applications.
• In the vicinity of the grounding system where interference
problems are suspected.
• In places of more line construction crossings or parallel
locations to determiner their interference and its
elimination.
• To eliminate the interference at insulating joints.
• Vulnerable locations with drastic change in soil resistively.
• Where corrosion has already been determined.
• At HT overhead line crossings and selected locations
where HT overhead line is in the vicinity of main pipeline
• At any other location considered vulnerable.
Field Measurements and Evaluations
Measuring Probes may be utilised most frequently for the
following
field measurements.
• The determination of polarization potential of pipeline (
without IR drops
• The determination of Cathodic protection effectiveness
using criteria of the protective current density on a defined
steel area.
• The determination of the corrosion danger or degree of
Cathodic protection Of underground steel structure
affected by stray current. .
• Measurement of on potential pipeline to soil.
• Measurement of on potential metallic electrode to soil or
off potential metallic electrode to soil
• Measurement of current entering the auxiliary metallic
electrode or discharging from the metallic electrode.
Field Measurements and Evaluations
•
•
•
Measurement while reducing the stray current interference
at a foreign pipeline
Measurement to reduce the stray current interference at
insulating joint
utilization of the Pearson holiday detector while measuring
signal above the metallic electrode with area of 100cm2 as a
comparative standard for the purpose of quantification's of
holiday in the coating.
Measurement of On Potential Pipe to Soil
V
100 10
2’
2
1
1’
COATED PIPELINE
CU-CUSO4
ELECTRODE
MEASURING PROBE
100
10
Measurement of Off/ On Potential Metallic Electrode to
Soil
V
100 10
2’
2
1
1’
COATED PIPELINE
CU-CUSO4
ELECTRODE
MEASURING PROBE
100
10
Measurement of On Potential Pipeline to Soil and
Current entering the Auxiliary Electrode
V
mA
100 10
2’
2
1
1’
COATED PIPELINE
CU-CUSO4
ELECTRODE
MEASURING PROBE
100
10
Measurement AND Reducing Stray Current
Interference at a Foreign Pipeline
mA
VARIABLE RESISTOR
100 10
3’
3
1
1’
4
5
5
CATHODICALLY PROTECTED PIPE
CU-CUSO4
ELECTRODE
MEASURING PROBE
100
10
FOREIGN INTERFERRED
PIPELINE
Measurement and Reducing Stray Current
Interference at an Insulating Joint
mA
VARIABLE RESISTOR
100 10
3’
3
1
1’
4
5
5
PROTECTED
PIPE
COATED PIPE
CU-CUSO4
ELECTRODE
MEASURING PROBE
100
10
INSULATING JOINT
Casing Pipe Measurement
road
Measurements
• Resistance
Potential
difference
between pipeline and
•
casing pipe
contact between casing and pipeline
I=I +I
s
I
Ltg
Ltg
-
I
cathodic
protection
station
s
pipeline
+
anodes
U
uncoated casing
in V
Cu/CuSO
4
- 1,1
protective potential criterion
- 1,0
- 0,9
- 0,8
- 0,7
- 0,6
potential shift on area of casing in contact with pipeline
Corrosion risk Analysis of Carrier Pipe in the Casing
Case 1
casing pipe
pipeline
protective current
coating
line current
coating defect
•casing pipe isolated from the pipeline
electrolyte in the ring room of the casing pipe
•no no
• coating defect within the annular space
Î no corrosion risk
Corrosion risk Analysis of Carrier Pipe in the Casing
Case 2
coating defect
casing pipe
protective current
coating
line current
pipeline
isolated from the pipeline
•casing pipe
no
electrolyte
in
the
ring room of the casing pipe
• coating defect within
the annular space
•
Î no corrosion risk
Corrosion risk Analysis of Carrier Pipe in the Casing
Case 3
casing pipe
protective current
coating
line current
coating defect
pipeline
Electrolyte
isolated from the pipeline
•casing pipe
in the ring room of the casing pipe
•electrolyte
•no coating defect within the annular space
Î no corrosion risk
Corrosion risk Analysis of Carrier Pipe in the Casing
Case 4
metallic contact
protective current
coating
line current
coating defect
pipeline
contact between casing pipe and pipeline
•metallic
no
electrolyte
the ring room of the casing pipe
• no coating in
defect
within the annular space
•
Îno corrosion risk
Corrosion risk Analysis of Carrier Pipe in the Casing
Case 5
protective current
coating
line current
coating defect
Electrolyte
pipeline
isolated from the pipeline
•casing pipe
in the ring room of the casing pipe
•electrolyte
•coating defect within the annular space
Îno corrosion risk
Corrosion risk Analysis of Carrier Pipe in the Casing
Case 6
protective current
coating
line current
coating defect
pipeline
contact between casing pipe and pipeline
•metallic
in the ring room of the casing pipe
•no electrolyte
coating
defect
within the annular space
•
Îno corrosion risk
DIFFERENCE BETWEEN GALVANIC ANOD /
IMPRESSED CURRENT CP SYSTEM
Sl.No
Galvanic
Impressed Current
1
Require no external power
External power required
2
Fixed Driving Voltage (EMF)
Voltage can be varied
3
Limited Current
Current can be varied
4
Suitable
for
electrolytes
LOW
resistivity Can be used in almost any resistivity
environment
5
Suitable for low current
requirements.
/LOW Life Can be designed for almost all current
/ Life requirement
6
Frequent monitoring and maintenance Regular Monitoring / maintenance
not required
required.
7
Remote monitoring and control is Can be designed for remote monitoring
difficult
and control.
8
Measurement of instant OFF-OFF Can be designed for measurement of
potentials is difficult if not impossible
instant OFF/ON potential
9
Create minimum interference problem
10
Suitable for offshore plate form / Usually not recommended for such
Structures,
temporary
cathodic applications.
protection etc.
Interference
considered
problem
must
be
TYPICAL VERTICAL GROUND BED
Anode header cable 1x35 Sq.mm. copper
1.75 M
0.25 M
Anode conn. Cable
1x10 mm2
copper
3.5 M
4.0 M
25 Cm
Bore hole dia = 25.4 cm.
Bore hole depth = 350 cm
Backfill material = Petroleum grade coke breeze in sieve size of 1mm or less
TYPICAL HORIZONTAL ANODE BED WITH MS RAIL
WHERE SOIL RESISTIVITY INCREASES WITH DEPTH
OR ROCKY AREA
Anode header cable 1x35 mm2
1x10 mm2 cable
1x10 mm2 cable
3METRE MS RAIL
Selecting Corrosion Mitigation methods.
Coating And Cathodic Protection
• Ideally, perfect coated pipe should not take
any current.
• However, even newly coated pipe requires current
for making it above protection.
• The modern pipeline corrosion control work
Comprises the use of good coatings in combination
with suitable CP system as the main lines of defense.
• Supplementary defense, such as use of insulated
coupling, interference mitigation device, local
environmental control etc. reinforce the main defense.
Selecting Corrosion Mitigation methods.
Mitigation Of Internal Corrosion in Pipelines:
Main Contributing factors
• Corrosive nature of the transported product.
• Moisture/Traces of water, CO2, oxygen, H2s, bacteria etc.
•
Erosion - Corrosion.
Mitigation Measures
• By regular and periodic pigging of pipeline for internal
cleaning.
• Introduction of corrosion inhibitor in pipeline
• Ensuring transported product free from moisture &
corrosive compound.
Dealing with challenges in rehabilitation
of old operating pipelines.
Challenges
•
•
•
•
•
•
Mostly CTE (over the ditch) coated
High current density i.e poor coating.
Conventional CP system.
Inconsistent SEB Power availability/Theft of Solar
panels.
Highly corrosive soil.
Low frequency ERW mainline pipes.
Requirement of Coating Surveys
• Coating deteriorates with passage of time & the load
on CP system increases day by day.
• It slowly reaches a limiting condition where any
amount of additional CP protection does not improve
the situation.
•
Therefore, identification of coating defects with
highest accuracy becomes very important, so that
coating repairs & subsequent Line Protection is
achieved in shortest possible time.
Selecting Suitable Surveys
CURRENT
ATTENUATION
TECHNIQUE
(CAT)
PEARSON
SURVEY
Coating
Surveys
DC VOLTAGE
GRADIENT
SURVEY(DCVG)
CLOSE INTERVAL
POTENTIAL
SURVEY (CIPS)
Selecting suitable Surveys
CURRENT ATTENUATION TECHNIQUE (CAT)
9
Over all assessment/classification of
coating quality for
different stretches.
9
Most Suitable coating surveys for priority fixing for coating
refurbishment.
DC VOLTAGE GRADIENT SURVEY(DCVG)
9
DCVG for pin pointing the coating defects.
APPROACH
9
Combination of CAT & DCVG for coating assessment &
finalizing locations for refurbishment.
PEARSON SURVEY
KEY
OPERATOR
SIGNAL GENERATOR
RECEIVER
GROUND
TLP
LOCATOR COIL
20 FEET
PRINCIPLE OF ELECTROMAGNETIC CURRENT
ATTENUATION SURVEY
Transmitter
Test Post
Earth Stake
Receiver
Current loss through
coating
d
Roa
Location of 1st
Reading
Current loss at
defect
Current flow in
pipe
Coating Defect
d
Roa
Location of 2nd
Reading
CAT SURVEY
C1 = CURRENT AT POINT 1
C2 = CURRENT AT POINT 2
L = DISTANCE BETWEEN POINT 1 & 2
d = DISTANCE FROM THE PIPE CENTER TO THE BOTTOM
COIL
ACCORDING TO LENZ LAW Vb = K C1/ d
Vt = K C1/ d+ s
Vb = VOLTAGE AT THE BOTTOM COIL
Vt = VOLTAGE AT THE TOP OF COIL
k = CONSTANT
S = DISTANCE BETWEEN TOP & BOTTOM COIL
1
2
CAT SURVEY
Vt / Vb = d/ d+s or d = Vt . S/ (Vb – Vt)
SUBSITUTING THE VALUE OF d IN EQUATION 1
Vb = KC1 .(Vb – Vt) / Vt xs
C1 = s Vb.Vt / K( Vb-Vt)
THUS RECEIVER CAN MEASURE BOTH C1 (CURRENT)
AND DEPTH d AT THAT POINT.
THEORTICALLY ,THE SIGNAL IS ATTUNUATED LOGARITHMICALY ,
THEREFORE CURRENT C1 IS CONVERTED
TO DECIBLE AND STANDARISED db/ Km
ATTUNUATION AT POINT S1= 20 Log C1 db
ATTUNUATION AT POINT S2 = 20 Log C2 db
RATE OF ATTUNUATION BETWEEN 1 & 2 = R=L.( S2-S1)/1000
db/km
TYPICAL PLOT OF RESULTS OF CAT SURVEY:
DB LOSS PER KM
BAD
SECTION
FAIR SECTION
OK SECION
GOOD
SECION
100
300
200
DISTANCE IN METRES
400
500
CAT SURVEY
BASED ON DB LOSS OBSERVED FOR PIPELINE, COATING DEFECTS
CAN BE CLASSIFIED AS UNDER :
SL.
NO.
DB/KM LOSS
CLASSIFICATION
1.0
< 10 DB/KM
GOOD COATING
2.0
10 – 25 DB/KM
FAIR COATING
3.0
25 – 70 DB/KM
BAD COATING
4.0
ABOVE 70 DB/KM
MASSIVE DEFECT
DVANTAGES
SURVEY NOT REQUIRED WALKING ALL ALONG PIPELINE.
BETTER ACCURACY.
INDEPENDENT OF TRANSMITTER OUTPUT.
RECEIVER NOT REQUIRED ELECTRICAL CONTRACT
WITH
SOIL.
DISADVANTAGES
PIPE DEPTH CAN BE OBTAINED.
COATING
DEFECT
LOCATING
CAN
BE IDENTIFIED
INDIVDUAL
COATING
DEFECT
DIFFICULT
TO DETECT.
BY REDUCING SURVEY STEP.
EFECTIVENESS REDUCES IN CASE OF LARGE DIA
PIPE/POOR COATING.
GIVES ONLY QUALITATIVE INDICATION.
NO INDICATION OF CORROSION.
C VOLTAGE GRADIENT SURVEY(DCVG)
¾
THE DC VOLTAGE GRADIENT COATING DEFECT IDENTIFICATION
SURVEY IS VERY EFFECTIVE IN LOCATING THE SPOT COATING
DEFECT ALONGWITH ITS SIZE AND POSITION.
¾
ONCE IMPRESSED CURRENT THROUGH CP IS GIVEN TO THE
BURIED PIPELINE, A VOLTAGE GRADIENT IS ESTABLISHED IN THE
GROUND DUE TO PASSAGE OF CURRENT THROUGH THE SOIL AT
THE COATING DEFECT AREAS.
¾
THE POTENTIAL GRADIENT BETWEEN TWO CU/CUSO
4 A
ELECTRODES HELD BY ONE OPERATOR IS MEASURED ON
SENSITIVE VOLTMETER. WHILE CARRYING OUT THE SURVEY, THE
OPERATOR WALKS ALONG THE PIPELINE ROUTE, TESTING AT 2M
INTERVAL PREFERABLY ABOVE THE PIPE TO PICK UP THE VOLTAGE
GRADIENT FROM THE COATING DEFECT AREA.
DCVG SURVEY
¾ This method is used for locating and sizing of coating defect of buried
pipelines.
¾The technique is fundamentally based on measuring the voltage gradient
in the soil above a catholically protected pipeline.
¾The voltage gradient becomes larger and more concentrated the greater
the current flowing and the closer to coating defect. Larger the defect ,
the greater the current flow and hence the voltage gradient.
¾The DC Voltage gradient method utilize measuring millivoltmeter along
with two copper/ copper sulphate half cells .If placed half meter apart in
a voltage gradient, one half of cell will adopt a more positive potential
than other, which enables to find the direction of current flow.
¾Highest voltage gradient is recorded in close proximity of defect.
¾
WHEN A DEFECT IS APPROACHED, THE VOLTMETER RESPONSE
BEGINS TO INCREASE AND WHEN THE DEFECT IS PASSED, THE
NEEDLE
DEFLECTION
COMPLETELY
REVERSES
AND
SLOWLY
DECREASES AS THE SURVEYOR MOVES AWAY FROM THE DEFECT.
¾
BY RETRACING TO THE DEFECT, THE POSITION OF THE PROBES CAN
BE FOUND WHERE THE NEEDLE SHOWS NO DEFLECTION I.E. A NULL.
¾
THE DEFECT IS THEN SPOTTED MIDWAY BETWEEN THE TWO HALF
CELLS. AFTER IDENTIFICATION OF NULL POINT (EPICENTER) PIPETO-REMOTE EARTH POTENTIAL IS MEASURED AT THE HOLIDAY
EPICENTER AND IR DROP CALCULATED FOR ALL SUCH LOCATIONS.
THE VALUE OF PERCENTAGE IR DROP INDICATE THE EXTENT OF
COATING DEFECT.
D
C
V
G
P
R
I
N
C
I
P
L
E
DCVG SURVEY
VT= Applied voltage
• VOLTAGE DROP
VI=Potential difference
pipe to soil interface
Vs= voltage diff. Between
pipe/soil & remote earth
VT
VS
VI
CURRENT FLOW
REMOTE EARTH
PIPE
VT=
SOIL
Value of signal measured at test posts
VT = VI + VS
DCVG SURVEY
•
SIZING OF COATING DEFECT
S2 = 300 MV
S1 = 800 MV
400M
0
TP1
1000M
dx
d1
DISTANCE
COATING DEFECT
130MV
TP2
d2
DCVG SURVEY
¾
¾
¾
¾
¾
Measured voltage at TP1 say 800mv
Measured signal at TP2 say 300 mv
Drop between TP to TP2 500mv
Say defect is at dx from TP1which is 400 m from TP1.
Pipe to earth voltage P/RE= S1- (dx/ d2-d1) x (S2-S1)
= 800 – 400( 800-300 )/ 1000
= 600 mv
¾ If the epicenter to remote earth potential was observed
130mv
% IR = 130X 100 / 600 = 21.1% IR loss
¾ In general 6% IR % indicate a defect with bare steel I
contact with soil of app. 10sq cm( one meter depth)
Selecting suitable Surveys
CIPS Survey
9
Reflects the actual status of line protection for entire section.
9
Indicates interference problems, if any.
9
Detects deficiencies in CP system that go undetected during
routine monitoring.
STATION & MAINLINE
MAINTENANCE
Typical Pump Station layout
IC
12”MOV
12”
SLB
From
P/S
IC
To Next P/S
SRB
14”
14”
MOV
8”
12”MOV
8”
3”
14”
MOV
2”
12”
IFD
12”
12” MOV 12”
TM
6”
12”
8”
6”
12”
8”
TM
12” MOV
14” MOV
6”
E
H
10”
10”
MP-3
6”
TM
10”
6”
14”
14”
10”
10”
S/F
MP-2
14”
HSD
6”
14”
8” 8”
E
12” 12” MOV
14”
10”
12” MOV
TM
Strainer
12”
6”
6”
12”
12”
SK
ATF
MS
MP-1
H
IMPORTANT STATION EQUIPMENTS
¾MAINLINE PUMP/ENGINE/MOTOR
¾BOOSTER PUMP/MOTOR
¾EMERGENCY GENERATOR –DIESEL ENGINE
¾FIRE FIGHTING ENGINE
¾FIRE FIGHTING PUMP & GEAR HEAD
¾SUMP PUMP /OIL WATER SEPARATOR PUMP
¾AIR COMPRESSOR AND AIR VESSELS
¾SURGE RELIEF TANK AND SURGE RELIEF PUMP
¾VALVES
¾STRAINER
¾SEPARATOR FILTER
¾STATION MAIN INCOMING AND OUTGOING PIPELINE
¾STATION UNDER GROUND AND ABOVE GROUND PIPING
Maintenance Target:
•Maximize Economic Usage of equipment
•Maintain Equipment Reliability
•Technical Planning and Control of Maintenance Activities
•Reconditioning of parts
•Analyze equipment failure and performance
•Modifications in equipment for higher efficiency and
improvement
•Cultivate maintenance related expertise in maintenance
personnel
Maintenance Practice
•Corrective Maintenance : When the engine deviates
from its “desirable” performance conditions, it requires
corrective maintenance to get it back into desirable
performance condition
•Preventive Maintenance : To ensure “desirable”
performance, the regular or timely (running hour based)
maintenance taken is known as Preventive Maintenance
•Predictive Maintenance : This type of maintenance is
based on the current condition of different parameters like
Jacket Water, Lube Oil, Exhaust Gases, Vibration of Rotary
Parts
•Condition monitoring.
PRIME MOVERS FOR MAINLINE
PUMPING UNIT
1.
2.
3.
DIESEL ENGINE DRIVEN
MOTOR DRIVEN- FIXED SPEED TYPE
MOTOR DRIVEN VARIABLE SPEED TYPE
THE ENGINES ARE DRIVEN BY DIESEL FUEL
OR CRUDE FUEL . IN CRUDE OIL PIPELINE,
CRUDE OIL BEING AVALABLE DIRECTLY
FROM LINE , THE CRUDE FUEL ENGINE ARE
PREFERRED. FOR PRODUCT PIPELINE , THE
DIESEL FUEL IS USED.
MAINLINE PUMPING
UNIT WITH
AUXILIARY
EQUIPMENT
MAINLINE FACILITIES
• Boundary Pillar (BP)
• Turning Post (TP)
• Kilo Meter Post (KMP)
• Vent Pipe (VP)
• Test Lead Post (TLP)
• Caution Board
• Block Valve (BV)
• CP Station
•Repeater Station
•Repeater cum CP Station (RCP)
INSPECTION OF R.O.W.
• To observe surface condition
¾ Wash outs
¾ Leaks
¾ Encroachments
• To inspect the Markers & accessories
¾ Markers
¾ TLPs
¾ Block Valves
¾ CP / RCP stations
• To inspect Crossings & vulnerable locations and
special attention to suspended crossings, exposed
area etc.
TYPES OF MAINLINE MARKERS
•Boundary Pillars
•Test Lead Points
•Kilometer Posts
Contd….
MARKER BOARD
TYPES OF MAINLINE MARKERS
•Inter Mediate Posts
•Turning Points
•OFC markers
•Vent Pipes
•Warning Posts
KILOMETER POST
MAINLINE AREA
From Station Limit Valve of one station to the Station
Limit Valve of next station in normal width of 55 feet
STN Limit Valve
A
M
B
A
L
A
BV
12” dia Pipe
BV
15’
45’
We call this mainline area as ROW (Right Of Way)
J
A
L
A
N
D
H
A
R
MAINLINE LAYOUT
Position of M/L markers
IOCL
IOCL
KBPL
KBPL
TLP
VP
BP
VP
KMP
TP
154
Casing
Pipe
IOCL
KBPL
RO
A
D
Caution
Board
IOCL
KBPL
MAINLINE PATROLLING
• Daily Patrolling by Line Patrol Man (LPM)
• Surprise check by officers
• Mainline Patrolling by officers
• Daily Patrolling Report
• Monthly Patrolling Report
• Surprise Check Report
• Report on M/L Inspection by officers
ROW MAINTENANCE
• Providing missing M/L markers
• Painting of existing M/L markers
• Updation of Caution Boards
• Removal of bushes, trees etc from ROW
• Attending washouts
• Removal of encroachments
• Attending shorted cased crossing
• Refurbishing of Coat & Wrap
LIST OF PIPELINE REPAIRING TOOLS:
01.
LEAK CLAMP WITH SPARE GASKET
02.
CHAIN PULLEY BLOCK- 5 TON CAPACITY
03.
TRIPOD
04.
MECHANICAL SCREW JACK- 2 NOS.
05.
FULL ENCIRCLEMENT SPLIT SLEEVES
06.
WHEEL MOUNTED WATER TANKER-1000 LTRS
07.
PNEUMATICALLY OPERATED PIPE CUTTING SAW
08.
DIESEL DRIVEN AIR COMPRESSOR
09.
WHEEL MOUNTED SELF PRIMING PUMP
10.
PNEUMATIC SUMP PUMP
11
WELDING GENERATOR
Mainline Repair
A complete range of leak repairing tools should be kept in
stock in each base maintenance.
As majority of the pipeline emergency is caused due to minor
leaks , the same can be handled by the effectively handled by
the above tools for a safe and temporary cold repair with
minimum shutdown of operation.
In case of major leaks where a pipe joint or pup is required to
be replaced/inserted, it is an acceptable practice to carryout a
cold repair with a weld-end coupling as temporary repair to
make the line operational as the earliest and to arrest spillage
of product with prolong shutdown and spillage.
These temporary measure is made permanent at the
first opportunity by any of the following methods:-
a)
Welding of approved leak coupling
b)
Weld end coupling
c) Welding of sleeves
All welding should be carried out after ensuring the area is
“CLOCK
sleeving.
gasd)
free Providing
and the line
pressureSPRING”
is minimum
.
Physical Damage of pipeline
Pipeline after replacement of damaged
portion
LEAK CLAMP BEING
FITTED ON PIPELINE
WELDING OF LEAK CLAMP
CLOCK SPRING
Pilferage in Pipelines
Pipelines-- Fitting with welded patch
plate
CORROSION INHIBITOR
• IN CROSS-COUNTRY PRODUCT PIPELINE, WE ARE
USING CORROSION INHIBITOR TO MITIGATE THE
INTERNAL CORROSION OF PIPELINE.
•PRESENTLY UNICOR-J @ 6PPM IS BEING USED.
•CORROSION INHIBITOR FORMS A LAYER INSIDE
THE PIPE AND MAKE IT PASSIVE.
•IN CRUDE PIPELINE, NO C.I. IS INJECTED IN IOCL
PIPELINE
•BH CRUDE FORMS A LAYER OF WAX.
CORROSION PROBES & COUPONS
INTERNAL CORROSION RATE OF PIPELINE IS
BEING MONITORED BY :1) CORROSION COUPON :- INSTALLED AT
NRVs/AT SUITABLE LOCATIONS.
2) CORROSION PROBES:- INSTALLED IN
MAINLINE & WORKING ON RESISTANCE
MEASUREMENT.
INTERNAL CORROSION RATE
As per NACE RP-0775-91 corrosion rate is categorized as
Category
Low
Average corrosion
rate ( MPY)
< 1.0
Moderate
1.0 – 4.9
High
5 – 10.0
Severe
> 10.0
INTERNAL CLEANING OF PIPE
•
Pigging operation
Types of Pig: Cleaning Pig, Batching Pig,
Caliper Pig,Foam Pig, Instrument Pig
•
Purpose of pigging:
1.
2.
3.
4.
To clean the new pipe debris.
To know the inside pipe dia profile.
For inspection and measurement of any
corrosion or metal loss.
For generating initial pipe line data.
PIGGING AND ITS IMPORTANCE
• Scrapper pigs, which
have a central body
tube, or mandrel, and
various components like
PU cups and spring steel
brushes which can be
assembled onto the
mandrel to configure a
pig for a specific duty.
PIGGING AND ITS IMPORTANCE
• BI-DI or Batching
pigs, which have a
central body tube and
disc components can
be assembled onto
the body to configure
a pig for a specific
duty;