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 • • • • • • • • 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 • • • • • • 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 10 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. 11 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 12 Health Monitoring Surveys carried out in MGL • • • 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 • • • • 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 • • • • • • 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 • • • • 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: • Pipeline below cement concrete road. • Pipeline top cover 2.3 meter from road surface. • Total affected length of pipeline - 2.0 meter • Defects orientation - Between 9 & 3 O’clock position. • No sign of pitting / corrosion on pipe external surface 1 Site Photographs 2 Defect Schematic view 6 Non-Destructive Test (NDT) Performed • Magnetic Particle Inspection (MPI) • Ultrasonic Testing (UT) • Radiography Testing (RT) • Phased Array Ultrasonic Testing (PAUT) • Thickness measurement with special pencil type Probe Analysis: • Defect assessment / categorization as per BG standard & MGL. Defect assessment document (AI RF 008) • Extreme defects - 02, Severe defect - 01. • Maximum Thickness loss - 1.64 mm, Defect depth - 13 mm. • Defects on Weld seam / HAZ - 02 nos. • 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 • • • • • • • 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