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.
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
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
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
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.
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External base plate cathodic protection is required by code.
Ringwall sand pad foundation is most common.
High resistivity sand pad is intended to limit rate of corrosion, but also provides a challenge for cathodic protection system design and operation.
GACP – Mg, Zn anodes. Can also be “ribbon” type installed under tank bottom.
ICCP – HSCI, Graphite, MMO
Deep Anode Bed – “Remote” from tank bottom
Pro – Can be installed outside of tank ring wall
Con – High parasitic current losses to facility ground system / other buried foreign steel structures.
Shallow Anode Bed - Typically installed around periphery of tank.
Pro – Can be installed outside of tank ring wall
Con – Unlikely to provide any corrosion protection away from the tank perimeter.
GACP – Mg or Zn ribbon
ICCP – Mixed metal oxide typically
Pros – Even protection of tank bottom if designed and installed properly
Low parasitic current losses to foreign structures.
Cons – Typically installed prior to tank construction; cannot be replaced
Anode Horizontal Spacing – 2 to 5 foot depending on soil resistivity and depth of burial
Anode Burials Dept – 6 to 12 inch below tank bottom
Stationary Ref Cell.
Provides means to measure tank to earth potentials that indicate level of cathodic protection / corrosion protection.
Have a finite life.
Corrosion Coupons
Permit application of polarization formation / decay criterion.
Eliminate issues associated with “mixed potential” corrosion measurements.
Potential Monitoring Tubes.
External access for portable reference electrodes.
Eliminate issue with ref cell finite life.
Can back into the polarized potential based on actual measurements of current and voltage gradients under the tanks.