This document discusses advancements in cathodic protection design for on-grade storage tanks. It covers regulatory requirements for cathodic protection, foundation design considerations, different cathodic protection methods including galvanic anode and impressed current systems, criteria for cathodic protection system design, and recommendations to improve cathodic protection system specifications and validate protection criteria.

1. February 2021
ADVANCEMENTS IN CATHODIC PROTECTION
DESIGN FOR ON-GRADE STORAGE TANKS

2. TABLE OF CONTENTS
Slide 03 Regulatory Requirements
Slide 05 Foundation Design
Slide 08 Cathodic Protection Methods
Slide 14 Cathodic Protection System Design
Slide 20 Protection Criteria
Slide 24 Recommendations

3. REGULATORY REQUIREMENTS

4. CATHODIC PROTECTION IS REQUIRED BY CODE
49 CFR part 195.565
 “Breakout Tank” Defined
• Relieve Surges in a Hazardous Liquid Pipeline System
• Receive and Store Hazardous Liquid Transported by a Pipeline for Reinjection
and Continued Transportation by Pipeline.

5. FOUNDATION DESIGN

6. API 650 – Appendix B
COMMON TYPES
 Earth Foundation*
 Concrete Ringwall/Sand Pad*
 Reinforce Concrete Slab
*CP for Tank External Base Plate Required
Ring Wall / Sand Pad
Foundation

7. NACE SP0193
API 651
Industry Guidelines
SAND PAD PROPERTIES
 Chlorides < 10 ppm
 pH ≥ 5
 ρ > 5,000 Ω-cm (saturated)
 Sulfates < 200 ppm
 Sulfides < 0.1 ppm
 Chlorides – No Consensus
 pH ≥ 5
 ρ > No Consensus
 Sulfates – No Consensus
 Sulfides – No Consensus

8. CATHODIC PROTECTION METHODS

9. SYSTEM TYPES
API 651 – Section 6
 Galvanic Anode Cathodic Protection Systems (GACP)
• Rarely Specified
 Impressed Current Cathodic Protection Systems (ICCP)
GACP ICCP

10. ICCP SYSTEMS
API 651 – Section 9
 Deep Anode Bed
 Shallow Anode Bed
Deep Anode Bed Shallow Anode Bed

11. ICCP SYSTEMS
API 651 – Section 9
 Close Coupled Anode Bed
• Common for New Tank Construction
Close Coupled Anode Bed

12. CLOSE COUPLED SYSTEMS
New Tank Construction
 Concentric Ring Anode
 Parallel Anode
Concentric Ring Anode
Parallel Anode

13. GOOD TO HAVES
New Tank Construction
 Stationary Reference Cells
 Corrosion Coupons/UT Coupons
 Potential Monitoring Tubes
Stationary Reference Cell
& Corrosion Coupon
Potential Monitoring Tube

14. CATHODIC PROTECTION
SYSTEM DESIGN

15. Aspects that require consideration per API & NACE
WHAT DO WE MEAN – DESIGN?
 Proximity effects (Anode to
Cathode Distances)
 Soil electrolyte challenges
• The sand/electrolyte is never
uniform
• High resistivity materials are
used (poor conductivity)
• Confined areas/remote-earth
does not apply
 Steel Floor Plates
• Uneven – lap welds
• Different polarization
requirements - ASTM A516 GD
60/Heat Affected
Zone/Weld/Mill Scale

16. NACE SP0193 / API 651
ACCEPTANCE CRITERIA
 Proximity effects (Anode to Cathode
Distances)
 When the coupon and reference are
located approximately 133% to 200%
closer to the anode – The -850mV On
(less IR error)?
How much surface area does one PRE
cover ? ±0.25ft2
 The -850mV Off/IR-Free is seldom used
(poor design practices often make the
impossible to achieve)
 100mV formation/decay polarization

17. ADVANCED 3D CAE MODELLING
Advantages of 3D CAE Computational Modelling
 We can model from uniform to actual soil resistivities – not restricted

18. ADVANCED 3D CAE MODELLING
Advantages of 3D CAE Computational Modelling
 We can model the actual current and potential distribution and not assume “linear
analytical based uniform” values
 The analytical approach assumes uniform currents and uniform potentials – which
does not happen in reality

19. ADVANCED 3D CAE MODELLING
Advantages of 3D CAE Computational Modelling
The modelling is based upon CAD/eDrawings/converted PDF and replicates the actual
installation – actual polarization, resistivity, anode voltage drop, spread resistance, etc.,
are all accounted for - We can determine if the system works prior to installation

20. PROTECTION CRITERIA

21. NACE SP0169 – actually NACE SP0193
WHICH IS APPLICABLE?
 -850 mV ON
• Non-Starter
 -850 mV INSTANT OFF
• Difficult to Achieve ($)
 100 mV Polarized Potential
• Not Valid For “Mixed
Potential” Systems

22. Typical Tank Grounding System
MIXED POTENTIAL SYSTEM
 Anodic Metal - Steel
 Cathodic Metal - Copper

23. POLARIZATION CURVE
NACE SP0169
Potential
(-mV)
(+)
( )
ON Potential
OFF Potential
IR
IR
Native (Free Corroding, Static) Potential
100 mV
Polarization
100 mV Depolarization
“ON-IR” -850 mVCSE
“OFF” -850 mVCSE
Potential
(-mV)
(+)
( )
ON Potential
OFF Potential
IR
IR
Native (Free Corroding, Static) Potential
100 mV
Polarization
100 mV Depolarization
“ON-IR” -850 mVCSE
“OFF” -850 mVCSE

24. RECOMMENDATIONS

25. RECOMMENDATIONS
Bryan Louque – Audubon Companies
 Specification of on-grade tank CP systems must be improved to facilitate technical
and economic evaluation among system types
• Failure to do so will result in least cost / low value installation
 Critical for comparison are
• Anode spacing and depth parameters
• Anode current capacity versus design life
• Anode circuit redundancy
 Corrosion coupons and potential monitoring tubes must be emphasized / included
in system design to allow valid application of CP criterion
• Failure to do so will result in non-compliance / fines from regulators

26. RECOMMENDATIONS
Gerald Haynes – Elsyca Inc
 Using CLSM backfills we can avoid damage to CP and ensure uniform electrolytes.
 3D CAE modelling can verify/validate CP designs prior to or after construction and
are fully API 651/NACE SP0193 compliant.
 3D CAE modelling can determine protection and risks over the entire tank floor and
not just a 1% area.

27. THANK YOU
QUESTIONS OR
COMMENTS ?

28. People | Flexibility | Relationships | Experience
D:
D:
C:
C:
Vice President, Asset Integrity & Corrosion, Audubon Companies
blouque@auduboncompanies.com
918.514.5879
BRYAN LOUQUE
US Regional Manager, Corrosion Engineering, Elsyca Inc.
gerald.haynes@elsyca.com
GERALD HAYNES
913.221.3446
404-907-1261 720-651-1285