Mitigating Hazards and Corrosion Associated With HVAC Co-location Client Date Presenter
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Mitigating Hazards and Corrosion Associated With HVAC Co-location
ClientDate
Presenter
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
11
Parallelism
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
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 HVAC
HVAC
1.4 Miles0.22 Miles
0.5
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0.9 Miles
0.6
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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
HVAC
HVAC
1.4 Miles0.22 Miles
0.5
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0.9 Miles
0.6
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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
Sub-
Station
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 CouponsConsider:Coupon Placement –
How Can We Measure It?
External Corrosion CouponsConsider:Coupon Placement –
How Can We Measure It?
External Corrosion CouponsConsider: Measurement Method1 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 .01mAExample: 12.25 mA = 122.5 A/m2
CouponPipeline
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
HVAC
HVAC
1.4 Miles0.22 Miles
0.5
Mile
s
0.9 Miles
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 Grounding
Easy 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
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