O&M Workshop
CP of CGD Gas Pipelines
MGL’s Statistics
 CNG Outlets
: 281 nos.
 Steel pipelines
: 546 Km
 Polyethylene pipelines
: 5596 Kms
 District Regulating stations : 65 nos.
 Meter regulating Stations
: 211 nos.
 Daily Gas volumes
: 3.3 MMSCMD
Basic information of MGL Steel pipeline
Life Cycle
Design
Construction
Operation
Parameters
Grade
Pipe size
Location class
Thickness
Pressure Rating
Pipeline Network
Type of coating
Protection
Protection(CP)
Jointing
Hydro Testing
Valve spacing
Operating Pressure
Velocity
Surveillance
Leak survey
TR / TLPspacing
Steel pipeline
API 5 L Gr. B
18”, 12”, 10”, 8”, 6”,4” NB
Class IV
Mostly 9.52 mm(Min.6.4mm)
# 150 / # 300
Non- piggable
3 Layer polyethylene
RCC Tile & Warning Tape
TCP at construction / ICCP post commissioning
Weld Joint (100% RT)
31 kg/ 80 kg
3.0 km (Avg.)
18 bar (max)
20 m/sec.
Patrolling (once a day)
Once in a year
8 km / 0.5 km (Avg.)
CP Types in MGL
The supplementary method to protect pipelines against external corrosion
after coatings is Cathodic Protection.
Types of Cathodic Protection in MGL
 Sacrificial anode CP system / Temporary Cathodic Protection
 Impressed Current CP System / Permanent CP system
Comparison of the two methods of CP is elaborated below:
Sacrificial anode / Temporary CP details
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In CGDs, pipeline laying is not continuous. It is laid
in bits and stretches depending on permission
availabilities, road surface etc.
Since it takes time for the line to become
continuous, we provide TCP in coordination with
project pipeline laying activity
A cross functional joint visit is carried out to
finalize the pipeline orientation
Soil resistivity is taken over the pipeline route
In TCP, the number of anodes is designed based on
data of pipeline size, soil resistivity, interferences
expected, cased crossings expected etc.
Sectionalizing valve locations are fixed at every 3
Kms. These SVs have Insulating Joints on both
ends.
In MGL, TLPs are fixed at every 500 mtrs. We install
Magnesium anodes and permanent reference
electrodes at every TLP.
In MGL, we are also providing
TCP to the short steel length span
in PE-Steel nallah crossings.
Impressed Current / Permanent CP Systems Details
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Once the pipeline becomes continuous, we convert the TCP to PCP.
We have approximately 6-7 Kms of Steel pipeline network under 1 TRU.
The PCP system is first designed based on the inputs of surface area of pipeline to be protected
and soil resistivity of the section
The type of anodes used in MGL were initially Hi-Si-cr. We are now using Mixed Metal Oxide
(MMO) anodes as the consumption rate of the same is very low.
Our TRs are typically rated for 50V / 50A.
Wherever we face power interruptions, we install a dedicated battery bank and charger for the
TRU.
EXTERNAL POWER SOURCE
_
OBJECT TO BE
PROTECTED
+
PROTECTIVE
CURRENT
ANODE
Type of anode-beds in MGL
• Horizontal anode-bed
(a) Installed where there are no
space limitations
(b) Takes up a space of 30mtrs X
10 mtrs for 15 anodes.
(c) Horizontal Remote distance of
40m from pipeline (varies based
on design)
(d) Difficult to find space in
congested city environments
(e) Susceptible to cable / anode
damages in 3rd party work
Type of anode-beds in MGL
• Deepwell anode-bed
(a) Installed at most CP
station locations in
MGL as space is a
constraint in Mumbai
(b) Vertical remote
distance of 40m from
pipeline (varies as per
design)
(c) MMO anodes used
(d) Total drilled length –
100 m (40m inactive
length and 60m of
active length)
Schematic of Deep-well anode-bed in MGL
PVC Casing
Coke breeze slurry
MMO Anodes with dual feed cable
Dead weight
CP ASSETS IN MGL AND MONITORING STRATEGY
CP ASSET
QUANTITY (nos.)
MONITORING FREQUENCY
Transformer Rectifier Units
56
Physical (Quarterly). RMU (Daily)
Test Lead Points
807
Quarterly
Cased Crossings
113
Quarterly
Insulating Joints
318
Quarterly
External ER probes
72
Quarterly
Internal ER probes
13
Quarterly
Corrosion Coupons
70
Quarterly
Health monitoring surveys –
CIPL and DCVG
546 Kms
Once in 3 years
AC monitoring
1238
Once in a year / based on survey results
PE-Steel nallah crossings
413
Six monthly
Horizontal anode-beds
13
Six monthly
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Remote Monitoring of TRUs
Our journey of Remote monitoring of our
TRUs started in the year 2010
Our GSM loggers were installed in our TRUs
and our Diode stations
The data is monitored using SMS over
standard GSM mobile phone. The data is sent
to the mobile nos. programmed in the system.
Data broadcast can be programmed from one
broadcast / 5 mins to one broadcast / day.
Alarm messages are sent immediately without
waiting for the scheduled broadcast time.
The data of PSP, DC output voltage, DC
output current, AC supply voltage and run
hours are sent in the broadcast messages.
Alarm messages are generated in the events
of under-protection, over-protection, reference
fail and TR door open.
The central server is located at our office with
advantages of data storage and data recall.
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CP REMOTE
DATA SUMMARY
REPORT
SAMPLE
MGL is in the
process of
integrating this
system with
SCADA so that
data can be
received on
SCADA server only
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Health Monitoring Surveys carried out in MGL
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Soil resistivity survey using Wenner’s 4 pin method – once in 10 years
CIPL survey – Once in 3 years . CAT survey done on paved / concrete
roads
DCVG survey – wherever CIPL is abnormal
External Corrosion Direct Assessment (ECDA) is also being done for 130 Kms
as a pilot project. Indirect inspection has been completed and direct examination
is in progress.
Interference Studies carried out in MGL
DC / HVDC Interference Study:
Initially MGL had a lot of DC traction interference. MGL was installing Diode Stations at the interference
locations for mitigations wherein the stray current was being returned to the railway tracks. In 2016, DC
traction in Mumbai has been converted to AC. No interference due to DC traction anymore.
HVDC interference effects started to be observed after discontinuation of DC traction. On further
investigation, it was found that there exists a HVDC substation at Anjur phata which when operated in
monopolar mode makes ground the return path for the huge DC current. This then interferes with the
metallic utilities present in the radius.
AC Interference Survey
After traction systems were converted from DC to AC, a survey was carried out for the entire pipeline
network of MGL. Software simulation was done using ELSYCA software for steady state and fault
conditions of the power line. Necessary mitigations were the designed. Implementation of these
mitigation methods are in progress.
Foreign Pipeline Interference Survey
This is carried out during the commissioning of PCP system wherever MGL crosses foreign pipeline /
vice versa. The TR interrupter is programmed and switched on for the specified interval. The effect of
ON/ Off readings are observed on both pipelines. TLP has a provision for resistance bonding in case any
interference is observed.
Internal Corrosion Monitoring in MGL
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We are sending pipeline coupons obtained on opportunistic basis (diversions, hot taps
etc) for lab testing wherein the corrosion rate (in mpy) is calculated, and the roughness
factor is calculated (As per PNGRB regulations, clause no 5)
Internal ER probes are being installed at various locations which give us the reading of
corrosion rate directly in mpy. As on date we have 13 nos. of internal ER probes.
Gas analyzers are installed and gas composition analysis is also done on a regular basis.
Corrosion rate of samples / probes are less <1mpy in MGL
Case Study 1 – HVDC Interference Mitigation
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Identified in April 2016 on MGL pipelines
HVDC – High Voltage Direct Transmission
Used for bulk transmission of electricity
Normally operates in bipolar mode – Positive & Negative conductor
One of the conductor non-operational – Monopolar Mode – Earth is used as
second pole
Other operator pipelines also affected.
Chandrapur
MUMBAI
MUMBAI
Anjur Phata,
Kalyan
HVDC Interference on Pipelines
Pickup – Coating Disbondment
Discharge – Corrosion / Damage
Chandrapur
Discharge
Anjur Phata
Earth electrode
Maximum current discharge in earth – 1500A
Pickup
HVDC Substation –
Location – Padhge Village, Bhiwandi
Grounding Electrode – Anjur Phata, Kalyan
Current grounded – 1500 A
Operator – MAHATRANSCO (Maharashtra
State Electricity Transmission co. Ltd.)
• In service since – 1999
• Total Length – 752 kms(Chandrapur to
Padghe)
• Ratings : +/- 500 kV ; 1500 MW
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HVDC effect on MGL pipelines
 During monopolar operation of HVDC system and subsequent grounding at
Anjur phata, total 145 Kms (in 25-30 Kms radius) of MGL pipeline in vicinity is
getting affected. Creating multiple cathodic and anodic sites on pipeline.
 The areas getting affected are Thane, Kalwa, Rabale, Mahape, Kalyan,
Dombiwali, Ulhasnagar, Bhiwandi, Ambernath, Badlapur, Taloja, Kalamboli and
Kharghar
 These are all highly populated areas. Any damage to the pipeline and
subsequent gas leakage may have serious consequences considering the huge
population residing along the pipeline route.
 HVDC system at Padghe is operational since 1999. The details of affected
pipeline sections are as below
Pipeline Section
Commissioned in
Thane
2005
Majiwada to Mahape
2009
Taloja - Kalamboli
2012
Ambernath
2013
Kalyan Dombiwali Ulhasnagar
2016
Steps followed for HVDC interference study
 Stage I - interference identification –
(a) MSETCL informed MGL before starting the monopolar operation.
(b) On the designated dates, all TRs were switched off so that there would be no
confusion between CP DC readings and DC PSP being developed due to monopolar
(c) TLP readings taken during monopolar operation.
(d) Expected PSP was -0.44 V DC. PSP observed as max. -2.4V DC (classified as pick-up
location). PSP observed as +1.2V DC (classified as discharge location)
(e) TRs then switched ON to observe the effect. TR outputs adjusted accordingly.
(reduced at pickup and increased at discharge).
(f) Scenario got reversed when HVDC polarity got reversed.

(a)
(b)
(c)
(d)
Stage II – Software Simulation and Design of Mitigation
24 hrs data logging done at selected sites
Software used for Simulation – ELSYCA CATPRO
Inputs are pipeline details and HVDC load details.
Simulation done at normal condition and HVDC monopolar interference condition
Stage III – Installation of Remedial measures
TR installation at anodic areas
Re-arrangement of pipeline sections by changing the bonding
Change in TR output settings
Provision of localized grounding for cathodic shifts
SSPCs at pick-up locations to ground only excess HVDC current without
affecting the CP current.
(f) Readings again taken post mitigation, during monopolar operation and found
satisfactory.

(a)
(b)
(c)
(d)
(e)
-1.40
DC IR Free PSP for the Suraj Water Park to Gaimukh (R28)Pipeline Before and After Mitigation at
the Max HVDC Negative Monopolar Operation
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
[0]
[157.63]
[306.59]
[464.18]
[607.18]
[712.03]
[906.63]
[1081.19]
[1258.11]
[1448.05]
[1627.14]
[1840.09]
[1947.4]
[1998.76]
[2103.16]
[2267.95]
[2448.59]
[2632.74]
[2779.68]
[2998.71]
[3216.28]
[3394.56]
[3599.06]
[3691.07]
[3813.9]
[3982.11]
[4163.74]
[4388.53]
[25.93648467]
[204.1286805]
[397.338904]
[603.2553347]
[780.6759476]
[955.0790773]
[1065.533761]
[1138.658467]
[1234.184402]
[1426.992785]
[1638.556537]
DC PSP (V)
-1.20
IR Free PSP After Mitigation (V)
IR Free PSP Before Mitigation (V)
Underprotection Limit
Chainage No: (m)
Case Study 2 – Composite Repair on Pipeline
Pipeline Details
• Pipe Grade - API 5L Gr. B.
• Pipe wall Thickness - 10.1 mm (measured).
• Construction Year - 1998.
• Use of cement concrete coated pipe below Box culvert.
Occurrence Details
• Date - Night between 11th and 12th Nov’2021
• Segment - 18” Steel P/L from CGS Sion to Kamani (on LBS Road).
• Exact Spot - Pravin Shirgaonkar chowk, Opp. Hari Masjid
• MCGM Contractor using mechanical excavator (breaker) for breaking culvert & concrete.
Site Details:
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Pipeline below cement concrete road.
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Pipeline top cover 2.3 meter from road surface.
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Total affected length of pipeline - 2.0 meter
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Defects orientation - Between 9 & 3 O’clock position.
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No sign of pitting / corrosion on pipe external surface
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Site Photographs
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Defect Schematic view
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Non-Destructive Test (NDT) Performed
• Magnetic Particle Inspection (MPI)
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Ultrasonic Testing (UT)
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Radiography Testing (RT)
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Phased Array Ultrasonic Testing (PAUT)
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Thickness measurement with special pencil type Probe
Analysis:
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Defect assessment / categorization as per BG standard & MGL. Defect assessment document (AI RF
008)
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Extreme defects - 02, Severe defect - 01.
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Maximum Thickness loss - 1.64 mm, Defect depth - 13 mm.
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Defects on Weld seam / HAZ - 02 nos.
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NDT Results  No crack or other anomaly observed in the RT
 No any crack like defect was observed in PAUT
 No Indication of lamination observed in UT
Based on the above results, it was decided to apply a composite repair system after proper
designing
7
Surface cleaning
Surface preparation done
Steel re-inforcement
bands applied
First layer of glass fibre tape applied
after polymer application
Polymer and glass fibre tape
applied for 4 layers
Composite repair S wrap - bi-axial
woven Fibre glass material and preimpregnated with resin applied as
the final layer – 3 layers applied
Major On-going and Cold
up-coming
activities
wrap applied over the composite repair
Neoprene sheets applied over the pipe
Challenges of CP in City Gas Distribution
Damage of CP assets due to 3rd party excavations, coating damages due to 3rd party
No dedicated ROU. Other utilities in close proximity
Close proximity of gas pipeline with
water pipeline
Coating damages by 3rd party,
with metallic foreign objects touching the
pipeline
70% of pipeline is under Cement Concrete rendering surveys difficult
Extremely high traffic movement at most times because of which permission availability
for carrying out surveys / coating anamoly rectification becomes an issue.
Fair season for construction / maintenance is only from October – May (8 months)
Way Forward
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Plotting of all CP assets on MGL GIS platform along with details of coating rectification
locations. We are also planning on integrating the PSP data on GIS.
ECDA of entire pipeline network (on-going)
Installation of more internal ER probes at vulnerable locations.
Remote monitoring of TLPs (SMART TLPs)
UT of all aboveground pipelines on annual basis.
Need to develop a common CP monitoring mechanism / integrity analysis of CGD
pipelines.
Frequency of indirect indirect inspection techniques to be increased from once in 5
years to once in at-least 3 years