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Ac Interference
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Mitigating Hazards and Corrosion Associated With HVAC Co-location
Co-location of Pipeline and HVAC powerline is becoming more common as new right-of-way is needed.
Co-Location Effects
Continuous Corrosion Damage Slight to Moderate Personnel Hazard
Instantaneous Isolation Device/Equipment Damage Severe Personnel Hazard
Underground Arc Damage
High-voltage Line Co-Location
Number of towers Number of conductors
HVAC: What To Look For
Number of insulators Height of towers
HVAC: What to look for
AC Coupling: Capacitive
AC Coupling: Resistive
AC Power
Induced AC
AC Coupling: Inductive
Valve YardHIGH Personnel DangerHIGH Risk of Equipment Damage
Block ValveMODERATE Personnel DangerHIGH Risk of Equipment Damage
Well SiteLOW Personnel DangerMODERATE Risk of Equipment Damage
AC Coupling: Resistive
11
Two Approaches to AC Mitigation
Goal: Reduce risk of equipment damage, personnel hazard, and AC corrosion
Modeling Design Engineered approach Requires tons of field work Model output is dependent upon
quality input and parameters used Does not take advantage of
available natural grounds Generally very expensive
Field Design Practical approach Designs sometimes need to be
adjusted during/after installation Takes advantage of available
resources Generally less expensive
Two Approaches to AC Mitigation
Modeling: How much grounding do I need to prevent anything bad from happening?
Answer: A ton 0.6 M
iles
Two approaches to AC Mitigation
Field Design: Address the issues step by step
Protect personnel first
Identify threats to the asset
Add corrosion protection and re-test
0.6
Mile
s
C
C CC
C C
FLANGE INSULATION KITS
INSULATED UNIONS
INSULATED TUBING FITTINGS
Isolation Equipment Damage
1. Eliminate unnecessary isolation devices
2. Bond across necessary isolation with decoupling devices
3. Use robust isolation devices in lightning prone areas
Prevention
Occurs when high amounts of current discharge off a pipeline to return to a source.
Electric Generation
Substations
HVAC Towers
Direct Discharge Damage
Install High Current Drain Points between pipeline and return structure.
Bare Copper Conductor
Decoupling Device
Protective Anodes
Prevention
Personnel Hazards
Prevention
A carefully engineered, properly built ACLM system using components specifically designed for the purpose.
De-Coupling Devices
Gradient Control Mats
High Resistivity Backfill
Galvanic Cathodic Protection for Mats
PCR
SSD
Prevention
Gradient Control Mats
Installation of Magnesium Anodes Under Mat Area
Gradient Control Mats
Gradient Control Mats
Finished Exothermic Weld Connection
Gradient Control Mats
Properly Coat Finished Connection
Gradient Control Mats
Magnesium Anode Installation
Properly Sized Lead
Minimize Lead Length
Exothermic Connection to Mat
De-Coupling Devices
SSD
Pin-Brazed directly to pipe
De-Coupling Devices
SSD
Coupling nut attaches to pipe
Mounted Close to the Ground
Ready to Cover
AC Power
Induced AC
AC Coupling: Inductive
Does AC Really Cause Corrosion?
YES
A specific AC corrosion morphology
Proven results in the lab
Observed and recorded field occurrences
Why are we seeing this now?
Factors influencing AC corrosion rate: Induced AC Potential Discharged AC Current Density Defect Size Isolation From Ground Soil pH Frequency Changes in Pipeline/Powerline Geometry
What Does AC Corrosion Look Like?
Morphology Characterized by
Hard Tubercle
Corrosion Product
Soil @ Coating Defect
What Does AC Corrosion Look Like?
Coating
Disbondment at the Coating Defect Area
What Does AC Corrosion Look Like?
Active Corrosion
What Does AC Corrosion Look Like?
Smooth Rounded
Pits within Pits
What can we measure?
NACE: Keep pipe/soil AC potentials below 15 VoltsSafety Standard Only!
AC Corrosion State-of-the-Art: Corrosion Rate, Mechanism, & Mitigation Requirements #35110
AC CURRENT DENSITY AC CORROSION RISK0-20 A/M2
NO or LOW LIKELIHOOD20-100 A/M2
UNPREDICTABLE100+ A/M2
VERY HIGH LIKELYHOOD
The Prinze Diagram
How Can We Measure It?
External Corrosion Coupons
Consider: Coupon Size
~1 CM2 yields the most accurate results
How Can We Measure It?
External Corrosion Coupons
Consider:
Coupon Placement
How Can We Measure It?
External Corrosion Coupons
Consider:
Coupon Placement
How Can We Measure It?
External Corrosion Coupons
Consider: Measurement Method
1 CM2 Coupon 1.0 mA = 10 A/m2 on pipeline
Meter MUST have low-range AC
current reading mode with a 0.1
mA resolution or better
Fluke 179 will read to .01mA
Example: 12.25 mA = 122.5 A/m2
Coupon
Pipeline
Mitigating AC Corrosion
Field Design Methodology1. Analyze Parallelism
2. Designate Potential High Current Drain Points
3. Install Coupons for Current Density Measurement
4. Connect Available Natural Drains
5. Install Additional Grounding Where Required
0.6
Mile
s
C
C
C CC
C C
Mitigating AC Corrosion
De-Coupling Devices: Kirk Cell
(Polarization Cell)
PCR (Polarization Cell
Replacement)
SSD (Solid State Decoupler)
Mitigating AC Corrosion
Good natural drains:
Well Casings
Road Casings
Plant Grounding Systems
Bare Pipe
Large Bull Guards
Drainage Culvert
Adding additional drains:
Gradient Control Mats Part of personnel safety equipment Grounding is provided by multiple anodes SSD decouples mat from Pipeline
Mitigating AC Corrosion
Mitigating AC Corrosion
Adding additional drains:
Deep Vertical GroundGenerally 100+ ft. deepCopper core surrounded by backfill Conductive concrete increases ground contactA PCR is used to de-couple the pipeline from the ground
PCR
Mitigating AC Corrosion
Adding additional drains:
Linear Cable GroundingEasy To install at pipe depthLong runs must be connected via PCR at every road and creek crossingSubject to excavation damage if not clearly marked on one-callsMay act as a secondary conductor
PCR
Mitigating AC Corrosion
Adding additional drains:
Zinc Anodes
Easy To install with coupon test stations
Provide a local point drain that each CTS location that can be easily disconnected if needed
Co-Location Threats
InstantaneousPersonnel Hazard Isolation DamageDischarge Damage
ContinuousCorrosion Damage
Mitigation Methods
Gradient Control MatsDe-Coupling DevicesDesigned Discharge Points
Coupon Test Stations (Monitoring)Gradient Control Mats (If Used)Engineered Grounding Deep Type Linear Cable
Recap
References
Technical Report on the Application & Interpretation of Data from External Coupons Used in the Evaluation of Cathodically Protected Metallic Structures #35201
AC Corrosion State-of-the-Art Corrosion Rate, Mechanism, & Mitigation Requirements #35110
49 CFR 192.467 (f)External Corrosion Control; Electrical Isolation
NACE SP0177-2007 Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems
Questions?
Jordan Groodyjordan.groody@bass-eng.com(903) 759-1633
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