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

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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