Why is Cathodic Protection Important? Preserve Assets Avoid - - PDF document

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Why is Cathodic Protection Important? Preserve Assets Avoid - - PDF document

Sep 06, 2023 123 likes •446 views

Cathodic Protection for ASTs Presented by: James T. Lary Corrpro Companies, inc. 1055 West Smith Road Medina, Ohio 44256 jlary@corrpro.com 330-241-6615 Why is Cathodic Protection Important? Preserve Assets Avoid Disruption of

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Cathodic Protection for AST’s

Presented by: James T. Lary Corrpro Companies, inc. 1055 West Smith Road Medina, Ohio 44256 jlary@corrpro.com 330-241-6615

  • Preserve Assets
  • Avoid Disruption of Service
  • Enhance Safety
  • Prevent Leaks
  • Governmental Regulations
  • Reduce Maintenance

Costs

Why is Cathodic Protection Important?

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Terminal Tankage

Main Line

M

Valve OPS Inspection Meter

M

No OPS Inspection OPS Inspection Stops (Enforcement Policy) Loading Terminal

Product Tank (Terminal) Product Tank (Terminal)

Breakout Tank

M

Main Line

Valve OPS Inspection Meter

M

Product Tank (Breakout)

M

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Charleston, WV Spill

The investigation found that two small holes ranging in size from about 0.4-inch to 0.75-inch in the bottom of the 48,000- gallon tank 396 were caused by corrosion, likely resulting from water leaking through holes in the roof and settling on the tank

  • floor. Furthermore, the CSB inspection

found a similar hole penetrating the bottom of nearby tank 397, containing the same chemical at the facility, located in

  • Charleston. Other tanks also showed

multiple signs of pitting and metallurgical damage, investigators said. The growing corrosion in these tanks went unnoticed until the bottom of 396 was breached and up to an estimated 10,000 gallons of product made their way through the underlying mixture of soil and gravel under the facility and into the Elk River on January 9, 2014.

  • Causes of Corrosion
  • Cathodic Protection Applications
  • Installation & Maintenance
  • Rectifier Monitoring

What we will cover….

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Early Oil Tanks & Piping did not Employ CP

IRON OXIDE REFINING MILLING STEEL CORROSION IRON OXIDE

THE PROBLEM…..

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Anodic Area

  • 600mV

Cathodic Area

  • 550mV

SAND CURRENT FLOW

External Corrosion of Tank Bottom

MFL Floor Inspection

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SAND CURRENT FLOW

Corrosion Cell Caused by Foreign Material in Sand Cushion

CLAY

Steel Tank Floor

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DRY SAND MOIST SAND WATER

Corrosion Caused by Poor Water Drainage

New Bottom (Anode)

CURRENT FLOW SAND SAND

New Steel Coupled to Old Steel

Old Bottom (Cathode)

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8 Leak detection grove under under bottom Tank bottom required 30% floor replacement after 5 years in service

Concrete Slab

Types of Cathodic Protection

Galvanic: Current obtained from a metal with a higher energy level. Impressed Current: Requires external power source (transformer rectifier).

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System Characteristics

Galvanic Impressed

No external power  External power required Fixed driving voltage  Voltage can be varied Limited current  Current can be varied Small current requirements  High current requirements Used in lower resistivity  Used in almost any environment resistivity environment  Usually negligible  Must consider interference interference with other structures Above Ground Storage Tank With Galvanic Anodes

Anodes Tank Anodes

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10 Above Ground Storage Tank With Galvanic Anodes Is Protection Being Achieved?

Anode Tank Uncoated Tank Bottom Tank Grounded to Other Structures

Test Box Anode Cells Tank

Galvanic Anodes

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  • With the advent of secondary containment

liners for AST’s, some oil companies initially installed galvanic (zinc or magnesium) anode cathodic protection systems. Many of these same companies have now abandoned this approach due to the inability to obtain effective levels of cathodic protection or limited system design life.

  • The industry preference for cathodic protection

for large AST’s is now impressed current.

Galvanic Anode Installation on AST. Note that anode life and current output are dependent upon sand / backfill conditions. Reference cells were rarely installed to monitor performance. Galvanic Anode

(Many galvanic systems installed by tank contractor)

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Recommended Practices

API-651 - Cathodic Protection of Aboveground Petroleum Storage Tanks: “Galvanic anodes method is not practical for protection of large bare structures.” NACE RP0193-2001 - External Cathodic Protection of On- Grade Carbon Steel Storage Tank Bottoms: “Galvanic protection systems can be applied to tank bottoms where the metallic surface area exposed to the electrolyte can be minimized through the application of a dielectric coating or the area is small due to the tank size or configuration.”

(+) (-)

Return Rectifier Anode CURRENT FLOW

Impressed Current Cathodic Protection

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Impressed Current Cathodic Protection System  Anodes  Rectifier  Wiring

Tanks & Piping

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14 Above Ground Storage Tank Vertical Impressed Current Anodes - Existing Tanks

Sand Anodes Rectifier Negative Connection

+

  • Concrete

Ringwall Tank Anodes Rectifier

  • +

Negative Connection Tank

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Anodes Junction Box Rectifier

  • +

Deep Anode

Tank

(+) (-) Rectifier

Tank Tank Tank

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Computer Guided Horizontally Bored Anode System

Tank

Rectifier (+) (-)

Anode Splice Box Anode Pipe Monitoring Pipe Anode Pipe

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ABOVEGROUND STORAGE TANK CATHODIC PROTECTION

3” PVC 20% Exposure Anode Material Anode Tube 10’ Typical Test/Access Station Grade Aboveground Storage Tank

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Rectifier Units

Explosion or Non Explosion Proof ? AC Input ? AC Availability ?

CP Applications for Re-bottomed or New Tanks

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CP Installation on Rebottomed Tank

Above Ground Storage Tank Bottoms with Secondary Containment

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20 Liner Floor Anode Conduit

CP Installation on Double Bottom Tank New Tank Construction with Liner

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21 Anode Reference Cells Tank Impressed Current Junction Box (-) (+) Rectifier

Anode & Reference Cell Placement in High Resistance Sand

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Installation of CP System on Lifted AST Installation of CP System on Lifted AST

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23 Cathodic Protection Survey (When Tank is Full) Tank

Rim Potential Measurements

Portable Reference Cell Soil (+)

? ?

  • 850mV
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24 Soil Access Station (Thru Liner or Asphalt)

Reference Cell Placement Under Tank Bottom (Note obtain and store native readings)

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Reference Cell Monitoring Conduit

Tank

Monitoring Conduit

Cathodic Protection Monitoring

  • Read rectifiers every

30 days.

  • Conduct annual

inspection (obtain potentials) by NACE certified individuals.

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26 Hot Asphalt Tank Bottoms

Stray Current ?

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Pipeline Integrity Inspections

Qualifications

  • f the corrosion engineer
  • Certified by N.A.C.E.

(National Association of Corrosion Engineers)

  • Experienced in Cathodic Protection
  • Experienced in Cathodic Protection of Fuel

Storage Systems

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Internal Corrosion

Anode Cathode Water / Sediment Fuel Product

Internal Corrosion

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Coating Anode Bolt Tank Bottom

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Recommended Practices

API-651 - Cathodic Protection of Aboveground Petroleum Storage Tanks: NACE RP0193-2001 - External Cathodic Protection of On- Grade Carbon Steel Tank Bottoms:

Iron Water Fire Water Piping

Pitting (concentrated) corrosion attack on ductile iron pipe.

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Questions?

Thank You

James T Lary Corrpro Companies, Inc. 1055 West Smith Road Medina, Ohio 44256 330-723-5082 email jlary@corrpro.com