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AC Interference Mitigation and Monitoring Dale Lindemuth, P.E. Director of Engineering Houston, Texas FOR TODAY AC interference causes and concerns Mitigation techniques Mitigation project example AC corrosion / PRCI research Monitoring Q&A Utilidors Come In All Shapes and Sizes – 69kV to 1,000kV (69kV and lower typically not a major concern, but can be) 2 Steady-State AC Interference on Pipeline from Changing Electromagnetic Field: SAFETY & CORROSION CONCERNS Time-Varying Electromagnetic Field Produced By AC Current In Overhead Lines (300-5,000 Amperes, 24/7) Soil Pipeline AC corrosion rates as high as 400 mpy (10 mm/yr) ! Ingredients for AC corrosion: • AC power lines (or other AC) • High quality coating • Low soil resistivity • Excessive CP/DC on pipe AC Interference on Pipeline from Power Line Fault: MAINLY SAFETY CONCERNS, ALSO COATING & EVEN PIPE DAMAGE (Limited Reported Cases) Fault Current – 10,00040,000 Amperes total not uncommon, <0.1 second duration Pipeline Shield (“Sky”) Wire To Adjacent Towers Counterpoise Cable To Adjacent Towers AC Interference on Pipeline from Power Line Fault Underground High-Voltage AC Transmission Systems Copper Ground Cable (Typ.) A C B B C A Steady -State Pipeline Pipeline A C B B C A Power Line to Ground Fault Utilidors – Joint Pipeline / Power Line Corridors 1. Rights-of-way are increasingly difficult to obtain for new pipeline projects and for new power line projects 2. An attractive option is shared rights-of-way, i.e. “utilidors”: • New and upgraded power lines in existing pipeline corridors • New pipelines in existing power line corridors 3. Future projections are for more and more utilidors 4. Advances in pipeline corrosion protection coatings reduce the grounding (“earthing”) often associated with older generation coatings: • • • • Reduced cathodic protection current demand (a good thing) Unsafe AC voltages (a bad thing) Increased propensity for AC influenced corrosion (a really bad thing) Increased need for AC mitigation ($$$$) 5. Good neighbors, “do no harm”: • Who is “responsible” for controlling AC interference? • Who pays initially? • Who pays long-term? 8 Measured Pipe Potentials Under Power Line Steady State Operations AC Volts 60 40 20 0 9 AC PIPE-TO-SOIL POTENTIAL (Volts) Datalogging reveals conditions overlooked by instantaneous (“spot”) measurements 30 25 20 15 10 5 0 12:00 PM 6:00 PM Midnight 12:00 AM 6:00 AM Noon 12:00 PM 6:00 PM Midnight 12:00 AM Knowing and tracking power line operations is essential 11 AC Mitigation & Control - North American Standards/Codes and Regulations • • • • • • • NACE International – Corrosion Engineering Professional Society IEEE – Institute of Electrical Electronic Engineers CSA – Canadian Standards Association US Federal Regulations CFR 192 & 195 US DOT Operator Qualifications (OQ) Operator In-House Requirements Typical Corrpro Project Requirements: • 15 VAC Above and Below Grade (Steady-State) • 3,000 – 5000 VAC during Fault for FBE • AC Current Density < 30 amps / sq.meter (SP0169) • New NACE Standard under development (TG430) to address AC corrosion based on probe AC/DC current density and corrosion rate (Corrpro/MetriCorr/Elsyca research for PRCI) How far is far enough? • 1 meter per kilovolt rule-of-thumb: • 138kV = 450 feet • 230kV = 750 feet • 500kV = 1640 feet • European standards: • Overhead rural – 3000 feet • Overhead urban – 1000 feet • Underground, rural & urban – 150 feet • Typical consultant’s answer: it all depends, pay us to study it October-2015 INGAA Report (66 pages) 14 October-2015 INGAA Report – lots of look-up graphs 15 Many Complex Factors Contribute to AC Interference & Determining Effective Mitigation Pipeline: • Pipeline vs Transmission Line Geometry and Proximity • Length of Parallelism and Crossings • Coating Quality (better quality coating causes increased AC interference, but is also easier to mitigate when there is a problem) • Cathodic Protection (excessive CP can increase corrosion rates in presence of high AC levels) • Magnitude and Variation in Soil Resistivities • Electrical Breaks in Pipeline, e.g. Isolation Flanges • Influence of Existing Nearby Pipelines Power Line: • Transmission Line Conductor Configuration • Transmission Line Phase Transpositions • Tower grounding and Shield/Sky Wires Connecting Towers Parallel Mitigation, e.g. Zinc ribbon or copper cable, is often the primary mitigation measure for new pipelines (Best Value) 17 Grounding with Galvanic Anodes Overhead AC Transmission Line Underground Pipeline Sacrificial Anodes Induced Voltage Without Anodes With Anodes Distance Deep Anode Grounds – Typically 50-300 Feet Depending on Design 1) 2) 3) 4) Zinc ribbon Magnesium ribbon Copper cable High-silicon cast iron anodes in coke breeze 5) Galvanized steel water pipe with threaded joints (???) 19 So what does AC mitigation cost? New construction – parallel mitigation - $7-$9/Ft. Existing pipelines – parallel mitigation - $18 - $30/Ft. “Point mitigation” - $10K - $25K per location depending on design needs 20 PROJECT EXAMPLE: Proposed 42” Pipe, 170 Miles, 7 Power Line Circuits to 500kV 21 Computer Simulations – Without Mitigation RIGHT OF WAY SCHEMATIC 5 AC Circuit 3 - 115KV AC Circuit 7 - 500KV AC Circuit 2 - 230KV AC Circuit 6 - 500KV AC Circuit 1 - 500KV AC Circuit 5 - 115KV Cypress Pipeline AC Circuit 4 - 230KV 4.5 Crossings not shown for clarity 4 3.5 3 2.5 2 1.5 1 0.5 0 0 20 40 60 80 100 120 140 160 140 160 STEADY STATE PIPE TO EARTH VOLTAGE - NO MITIGATION 120 VOLTS 90 60 30 15-Volt Maximum 0 0 40 60 80 100 120 MAXIMUM PIPE TO EARTH VOLTAGE UNDER FAULT CONDITIONS - NO MITIGATION 12,000 VOLTS 20 8,000 4000-Volt Maximum 4,000 0 0 20 40 60 80 100 22 CONSTRUCTION MILEPOST 120 140 160 Computer Simulations – With Mitigation RIGHT OF WAY SCHEMATIC 5 4.5 Crossings not shown for clarity 4 3.5 3 AC Circuit 3 - 115KV AC Circuit 7 - 500KV AC Circuit 2 - 230KV AC Circuit 6 - 500KV AC Circuit 1 - 500KV AC Circuit 5 - 115KV Cypress Pipeline AC Circuit 4 - 230KV 2.5 2 1.5 1 0.5 0 0 20 40 60 80 100 120 140 160 STEADY STATE PIPE TO EARTH VOLTAGE - WITH MITIGATION VOLTS 30 Single Ribbon Mitigation Double Ribbon Mitigation 15-Volt Maximum 20 15-Volt Maximum 10 0 0 20 40 60 80 100 120 140 160 MAXIMUM PIPE TO EARTH VOLTAGE UNDER FAULT CONDITIONS - WITH MITIGATION Single Ribbon Mitigation Double Ribbon Mitigation 4000-Volt Maximum VOLTS 4,000 4000-Volt Maximum 2,000 0 0 20 40 60 80 100 23 CONSTRUCTION MILEPOST 120 140 160 Is the AC mitigation working? STEADY STATE AC PIPE TO SOIL POTENTIAL WITH MITIGATION 20 Design, Computer Simulation at Peak Power Demand Installed, Actual VOLTS 15 10 5 0 0 20 40 60 80 24 100 120 CONSTRUCTION MILEPOST 140 160 Corrpro In Action: Multi-Channel AC/DC Close Interval Potential Survey (data every 2.5 feet) Corrpro-Unique Multi-Channel AC/DC Close Interval Potential Survey (data every 2.5 ft.) 26 Common AC Corrosion Thresholds AC Current Density AC Corrosion Significance Less than 2-3 A/Ft.2 (20-30A/Sq.M) No or Low Likelihood 3 – 10 A/Ft.2 (30-10A/Sq.M) Medium Likelihood Greater than 10 A/Ft.2 (100A/Sq.M) Very High Likelihood Even in the Presence of Apparently Effective CP Qualitative only! Nothing about rate of corrosion, which is what really counts! Right? Coupon Potential & Current Measurements (-) mAac/dc (+) (+) Vac/dc on / instant-off PIPE COUPON REF. (-) AC Current Density (A/sq.m or A/sq.ft) = Measured Current / Coupon Surface Area Refined Criteria from PRCI Research Average AC Current Density (A/Sq.M) iAC vs. iDC, and or ER probe corrosion rate Average DC Current Density (A/Sq.M) Corrosion rate Measuring is knowledge DC ‘On’ potential MetriCorr Logger with Remote Monitoring Option DC IR compensated Potential DC current density AC potential AC current density Spread Resistance Ref. Electrode Pipeline MetriCorr Probe Flush type Rod type Time-stamped, simultaneous data collection, as frequent as 1 set of readings (7 channels of data) every minute Examples from the field: Modest level of CP does protect, even under high AC Examples from the field: With high AC, too much CP increases corrosion Examples from the field Impact of temporarily disconnecting AC mitigation for CP surveys ** Don’t do it! ** ~470 mils/year!!! Corrosion Rate DC Pipe-to-Soil Potential DC Current Density AC Pipe-to-Soil Potential AC Current Density CONCLUSIONS 1. 2. 3. 4. AC interference can be accurately predicted. AC interference can be safely and economically mitigated. • With good engineering, there is no technical basis to seek alternate pipe or power line routes because of AC interference. AC mitigation systems can be reliably monitored and maintenance friendly. • Practical mitigation designs with pipeline operator input is essential. In the presence of AC, excessive CP or cathodic DC interference can increase corrosion rates dramatically. • AC corrosion can be controlled in part by optimizing CP levels – not too little, not too much, just enough. Thank you…Q&A Dale Lindemuth, P.E (832)474-5361 [email protected] Effective AC Monitoring Technique? VICIOUS CIRCLE OF AC CORROSION Induced AC Small defect Too much CP Pre-requisites Depolarization Increased AC current Ohm’s law Increased CP SELFFEEDING AUTOCATALYTIC CORROSION Reduced Spread resistance Alkalinity What’s it called? Corrpro: ACIM = AC Interference Mitigation Power industry: EMI = Electromagnetic interference Dale: AC interference What’s going here? If you focus on corrosion rate, the rest is secondary VDC-ON (Volt) VDC-Instant Off (Volt) iDC DC Current Density (A/Sq.M) VAC (Volt) iAC AC Current Density (A/Sq.M) Rs Spread Resistance (Ohm-Sq.M) Personnel Safety: Equipotential Gradient Control Mats at Corrosion Control Test Stations, Valves & Other Aboveground Fixtures Test Station Parallel Ribbon & Mat connected to pipe through DC-decoupler, a.k.a “PCR” or “SSD” 7’x7’ Zinc Ribbon Mat “Spiral” – 8 inches below grade under well-drained gravel pad Pipeline Parallel Zinc Ribbon Main Line Valve, Pig Launcher/Receiver, Fence Grounding 41 Characterizing Soil Resistivity Low resistivity = High AC corrosion; High resistivity = More mitigation needed RIGHT OF WAY SCHEMATIC AC Circuit 3 - 115KV AC Circuit 7 - 500KV AC Circuit 2 - 230KV AC Circuit 6 - 500KV AC Circuit 1 - 500KV AC Circuit 5 - 115KV Cypress Pipeline AC Circuit 4 - 230KV 5 4.5 4 Crossings not shown for clarity 3.5 3 2.5 2 1.5 1 0.5 0 0 20 40 60 80 OHM-CENTIMETER OHM-CENTIMETER APPARENT RESISTIVITY 10000000 1000000 100 120 140 160 Average 1-1.5-2.5 Feet Average 4-5-6.5 Feet Average 10-15 Feet Average 25-40-50 Feet Average 65-75-100 Feet Average - All 100000 10000 1000 0 20 40 60 80 100 120 140 160 CDEGS EQUIVALENT RESISTIVITY 100000 10000 1000 0 20 40 60 80 100 CONSTRUCTION MILEPOST 42 120 140 160 CEN-EN 15280 AC Corrosion Criteria 1 A/m2 (DC) – cathodic current J AC 3 J DC 30 A/m2 (AC) Since AC-influenced corrosion is related to AC & DC, criteria for pipes with CP will be related to a combination of AC and DC current density using coupons…or a tolerable corrosion rate determined using suitable ER probes PRCI RESEARCH: CEN-EN 15280 AC Corrosion Criteria Vs. Precision ER Probe Corrosion Rate • ER data set from 31 pipelines, 218 points • From US, South America, Europe & Asia • 20% of ER data doesn’t conform with AC/DC current density criteria • Analysis is input to PRCI AC corrosion guidance How Best to Detect/Monitor AC and DC Interference? OR Simple Coupon OR Simple Electrical Resistance (ER) Corrosion Rate Probe Complete Monitoring System – Sophisticated Technology but Straightforward to Use Established Electrical Resistance (ER) Corrosion Rate Technology R (Ω) w d L R ρm (T) L W d ρm (T) ρm (T0 ) (1 α)T T0 As “d” (element thickness) is reduced because of corrosion, resistance is increased. Resistance increase over time can be related to corrosion rate (assuming constant temperature). Tools in the ACIM Tool Box Corrpro’s engineering strength is knowing which tool to use when and why • Safe Engineering Services ACIM ($60K): • Right-of-Way (soil resistivity profile) • Hi-Freq (single soil resistivity) • PRCI ACIM ($6K) • Elsyca ($60K): • IRIS (AC interference & mitigation) • ACCorSolver (AC corrosion) • CatPro (CP and DC interference) • Spreadsheets • Field evaluations and simulations • Good ole engineering experience • Existing AC interference issues vs. proposed pipelines/powerlines Existing 180-Mile Pipeline 26 Power Line Circuits to 230kV