Cathodic Protection for on grade Storage Tanks and buried piping


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Cathodic Protection for on grade Storage Tanks and buried piping

  1. 1. Cathodic Protectionfor On-Grade Storage Tanks and Buried Piping John Fitzgerald Corrpro Freshwater Spills Symposium April 6-8, 2004
  2. 2. Why is Corrosion Control Important?• Preserve Assets• Reduce Maintenance Costs• Governmental Compliance• Preserve The Environment
  3. 3. What I Will Cover….- Causes of Corrosion- SPCC/State/OPS Regulations- Cathodic Protection Applications- Maintenance Requirements
  4. 4. Spill Prevention Control and Countermeasure (SPCC) Regulation (Implementation Required by 2/18/05 )- Provide buried piping that is installed orreplaced after August 16th, 2002 with aprotective coating and cathodic protection.- Should a section of line be exposed for anyreason it must be inspected for deterioration.If corrosion damage is found you must takeadditional examination and corrective action.
  5. 5. Federal Level (Breakout Tanks)a) Relieves surges in a hazardousliquid pipeline system or b) receiveand store hazardous liquid transportedby a pipeline for reinjection andcontinued transportation by pipeline
  6. 6. Breakout Tank Piping (DOT) OPS Inspection Valve M Meter ProductM Tank M (Breakout) Main Line
  7. 7. State Level- Approximately 25% of States nowrequire cathodic protection be installedand maintained on new, refurbished, orrepaired tanks in contact with soil or sandfoundations.- A number of other states are in theprocess of implementing regulationsgoverning AST’s.
  8. 8. Terminal Tankage OPS Inspection No OPS Inspection Valve Loading Product Product M Terminal M Meter Tank Tank(Terminal) (Terminal) OPS Inspection Stops (Enforcement Policy) Main Line
  9. 9. Corrosion Can be Defined as Either: Practical Tendency of a Metal to Revert to its Native State Scientific Electrochemical Degradation of Metal as a Result of a Reaction with its Environment
  11. 11. 1) ANODE2) CATHODE Anode Cathode3) ELECTROLYTE -600mV -550mV4) ELECTRICAL CONNECTION -575mV
  12. 12. Corrosion of Metallic Structure
  13. 13. Cathodic Area (+) Anodic Area Structure (-)Current Flow
  14. 14. Corrosion Cell on TankBottom Steel Tank Floor CATHODE ANODE CATHODE CURRENT FLOW SAND CLAY
  15. 15. Corrosion Caused byPoor Water Drainage WATER MOIST SANDDRYSAND
  16. 16. New Steel Coupled to Old Steel New Bottom (Anode) CURRENT FLOW SAND Old Bottom (Cathode) SAND
  17. 17. Galvanic Anode Cathodic Protection4 Current is obtained from a metal of a higher energy level
  18. 18. PRACTICAL GALVANIC SERIES Material Potential* Pure Magnesium -1.75 Magnesium Alloy -1.60 Zinc -1.10 Aluminum Alloy -1.00 Cadmium -0.80 Mild Steel (New) -0.70 Mild Steel (Old) -0.50 Cast Iron -0.50 Stainless Steel -0.50 to + 0.10 Copper, Brass, Bronze -0.20 Titanium -0.20 Gold +0.20 Carbon, Graphite, Coke +0.30* Potentials With Respect to Saturated Cu-CuSO4 Electrode
  19. 19. Galvanic Cathodic Protection on Coated Pipeline StructureMagnesiumAnode Current Flow
  20. 20. Cathodic Protection Test Station Test Station Coated PipeMagnesiumAnode
  22. 22. Galvanic Anodes• Typically limited to new piping, that has a good quality coating and electrical isolation.• If the particular location is lacking any of the above, an impresses current system may be warranted.
  23. 23. Internal Corrosion Fuel ProductWater / Sediment Anode Cathode
  24. 24. Internal Corrosion
  25. 25. AnodeCoating Bolt Tank Bottom
  26. 26. Conventional CP Systems for AST’s - Shallow (Distributed) Anodes - Deep Anode Groundbed
  27. 27. Impressed Current Transformer Rectifier Unit
  28. 28. Impressed Current SystemRectifier (-) (+) Anode Groundbed Pipeline (Structure) Current Flow
  29. 29. Rectifier (+) (-) Tank Splice AnodeTypical Depth 20’ Shallow Anodes
  30. 30. Rectifier Anode (+) (-) Tank Shallow Anodes
  31. 31. RectifierJunctionBox + - Anodes
  32. 32. Directional Boring Under Existing AST
  33. 33. Aboveground Storage Tank Test/Access Station Grade 10’3”∅ PVC 20% TypicalExposure Anode Material Anode Tube ABOVEGROUND STORAGE TANK CATHODIC PROTECTION
  34. 34. New/Refurbished ASTBottoms with or withoutSecondary Containment
  35. 35. Secondary Containment4 Environmental Protection4 Minimize Liability4 State and Local Regulations
  36. 36. New Tank Construction with Liner
  37. 37. Anode & Reference Cell Placement in High Resistance Sand
  38. 38. FloorConduit Anode Liner CP Installation on Double Bottom Tank
  39. 39. New Floor Installation on Existing AST
  40. 40. CP Installation on Rebottomed Tank
  41. 41. Installation of CP System on Lifted AST
  42. 42. Maintenance of Cathodic Protection Systems - Conduct Annual Testing - Meet NACE Criteria/Standards - Conduct Bi-Monthly Rectifier Checks - NACE Qualified Technicians
  43. 43. NACE Cathodic Protection Criteria• -850mV or more negative with current applied• -850mV “Instant off”• -100mV shift between “Instant off” and “Native”
  44. 44. Annual Cathodic Protection Survey
  45. 45. (+) -850mV Tank Portable Reference CellSoil ? ? Rim Potential Measurements
  46. 46. bovegroundtorage Tank Test / Access Stationade 3’ Typical Bullseye® Monitoring Reference Cell Tube Rim 25 Center 55 Rim On -1411 -698 -404 -601 -1455 Off -902 -664 -402 -578 -911 Potentials (mV)
  47. 47. Test Station StructureStray Current Monitoring Test Station
  48. 48. Computerized Potential Logging SurveyTest Backpack ComputerStation Unit Chainer/Wire Dispenser & Counter Reference Cells Pipeline
  49. 49. Monitoring• Record volts and amps every 30-60 days• Compare values to target setting• Conduct annual cp survey by NACE engineer• Maintain cp records
  50. 50. Bi-Monthly Rectifier Check
  51. 51. Visual Check of Volts/Amps
  52. 52. Record Keeping- Provides History- Computer Records/Data Collection Remote Monitoring Hand Held Computers Close Interval Surveys Data Printouts Flagging of Problem Areas Prioritize Action Items- As Built Drawings- Store Data & Records for Life
  53. 53. System Characteristics Galvanic Impressed8No external power 8 External power required8Fixed driving voltage 8 Voltage can be varied8Limited current 8 Current can be varied8Small current requirements 8 High current requirements8Used in lower resistivity 8 Used in almost any environment resistivity environment8 Usually negligible 8 Must consider interference interference with other structures
  54. 54. Recommended PracticesAPI-651 - Cathodic Protection of Aboveground Petroleum Storage Tanks: “Galvanic anodes method is not practical for protection of large bare structures.”NACE RP0193-01 - External Cathodic Protection of On-Grade Metallic Storage Tanks: “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.”
  55. 55. Questions…