This document discusses considerations for impressed current ground beds. It defines three types of ground beds - conventional, deep, and distributed - and explains where each is best suited based on soil resistivity and other factors. It also covers topics like ground bed layout, anode and backfill material selection, cable specifications, and venting requirements. The goal is to help readers understand how to design ground beds that match site conditions and protection needs.

1. MATERIALS
CONSIDERATIONS FOR
IMPRESS CURRENT
GROUND BEDS
Charlie Poore
NACE Senior Corrosion Technologist #53904

2. INTRODUCTION / OBJECTIVES
At the conclusion of this session, you should be able to:
• Differentiate between three types of groundbeds
• Define the location and type of a ground bed
• Select the anode and backfill materials to
complement the groundbed design

3. GROUNDBED DESIGN VARIABLES
• Amount of Structure to be
protected
• Coating Quality
• Current Attenuation
• Soil Resistivity
• Grou ndbed Depth
• Desired Groundbed Life
• Anode Material
• Backfill Material
• Cable Material
• ROW Limitations
• Aquifer issues
• Anode Spacing
• Power Availability
• Rectifer Type

4. IMPRESSED GROUND
BED TYPES

5. IMPRESSED GROUNDBED TYPES
Three Types:
• Conventional (Less than 50 ft. deep)
• Vertical or Horizontal
• Good for low to medium soil resistivity
• Deep (More than 50 ft. deep)
• Vertical
• Good for high soil resistivity
• Distributed and/or Continuous
• Useful in congested areas where electrical
shielding prevents the use of remote groundbeds.
• Useful in areas of poor coating

6. TYPICAL CONVENTIONAL GROUNDBED LAYOUT
• Shallow Vertical Groundbed
• Good for low to medium soil resistivities

7. TYPICAL CONVENTIONAL
HORIZONTAL GROUND BEDS
• High resistivity areas of solid rock-fractured surface
• Limited installation equipment
• ROW considerations
• Current output dependent on length of bed
• Sock or wire electrode configeration

8. TYPICAL DEEP WELL GROUNDBED LAYOUT
• Vertical Groundbed
• Requires a drilling rig
• Anodes are installed
on top of one another

9. TYPICAL DISTRIBUTED GROUNDBED LAYOUT
• Close Groundbed
• Useful in areas of electrical
shielding or poor coating
• Close or continuous
Pipe Inlet
Pipe Outlet
Compressor Station
Compressor
Rectifier
Anodes

10. IMPRESSED GROUND
BED LOCATIONS

11. GROUNDBED SEPARATION
11
• Conventional
• 200 to 300 ft to first anode
• Deep
• 10 to 20 ft from structure
• 100 ft to first anode
• Distributed
• 10 to 50 ft

12. REMOTE VS. CLOSE
12
• Remote Groundbeds: The pipeline area of influence
does not overlap the groundbed area of influence.
• Close Groundbeds: The pipeline lies within the
groundbed area of influence.
Pipeline
Pipeline area of influence Groundbed area of influence
Groundbed
Pipeline
Groundbed area of influence
Groundbed

13. VOLTAGE GRADIENT
13
• Overvoltage Concerns
• Excessive polarized potentials may result
in hydrogen evolution
• May cause coating disbondment
• Upper limit typically -1.20 volts CSE
(Peabody references -1.1 volts)

14. IMPRESSED CURRENT
GROUNDBED ANODES

15. • Approximately 50% of groundbed anodes
• Operates best in wet environments
• Chemically resistant
• Chill cast , Centrifugally spun or sand molds
• Solid or Tubular
• Consumption Rate: 1 lb/A-yr (1/2 lb in Coke)
• Sizes
– Varying diameters from 1.5 in. to 4.8 in.
– Varying lengths from 60 in. to 84 in.
SILICON CAST IRON ANODES

16. Dia
(in)
Length
(in)
Weight
(lbs)
Output
capacity
(A)
Properties
2.2 to
4.8
60 to 84 36 to 315 2 to 4 • Hard, brittle alloy
• Primarily center-
connected in
cylindrical shape
• Compression
connection
PROPERTIES OF SILICON CAST IRON ANODES

17. GRAPHITE ANODES
• Approximately 40% of groundbed anodes
• Excellent conductor for all environments
• Microcrystalline wax or resin treatment
• Consumption Rate: 2 lb/A-yr (1 lb in coke)
• Sizes
– 3 in. diam. by 60 in. long
– 4 in. diam. by 80 in. long

18. Size
(dia/length)
Weight
(lbs)
Output
capacity (A)
Properties
3” x 60”
bar
30 1.5 • Brittle matrix of carbon
• Porous – requires treatment
to seal
• Primarily center-connected –
hole drilled from one end
• Compression or threaded
connection
4” x 80”
bar
72 2 to 4
PROPERTIES OF GRAPHITE ANODES

19. • Approximately 10% of groundbed anodes
• Good for low pH and chloride environments
• Consumption rate: grams per/A-yr
• Varying configurations: Tube, Rod, Wire, Ribbon, Disk
MIXED METAL OXIDE ANODES

20. LINEAR MMO ANODE PRODUCTS
• Ensures uniform Current
distribution
• Useful in areas of electrical
shielding
• Reduces interference problems
• Long-line continuous anode
offers alternative to re-coating

21. CANISTER ANODES
• Coke breeze packaged around anode in sealed container
• Galvanized steel container quickly consumes leaving
anode in coke column
• Vertical or horizontal placement
• Designed for environments where coke placement is
difficult (mud, marsh, sand)

22. IMPRESSED CURRENT
GROUNDBED WIRE
AND CABLE

23. ANODE CABLE
Size
• Ranges from AWG #4 to AWG #10
• Standard #8 or #6 AWG
Length
• Specified by end-user
• Typically 10 – 15’ for conventional install
• Or determined by deep anode depth
Insulation
• HMWPE (110mils) industry standard
• Dual extrusion Halar or Kynar with outer layer
of HMWPE for severe environments

24. HMWPE CABLE
Copper
HMW/PE
• High Molecular Weight Poly-Ethylene
• Most commonly used cable for anode leads, header
cables and negative leads
• Exterior coating is 110 mils thick
• Strong resistance to abrasion, crushing, chemicals,
moisture and other elements.

25. DUAL EXTRUSION CABLE (HALAR/KYNAR)
Copper
HMW/PE
Kynar or Halar
• Has two layers of coatings making up the exterior jacket.
• HMWPE secondary coating (exterior) 65 mils thick and used
for abrasion resistance.
• Halar/Kynar primary insulation (interior) 20 mils thick and
highly chemical resistant.
• Used primarily in deep well anode ground beds where
chlorine gas is present.
• Used for impressed current anode beds in salt or brackish
water environments.

26. IMPRESSED CURRENT
GROUNDBED BACKFILL

27. BACKFILL SELECTION CONSIDERATIONS
27
• Coke Breeze
• Low resistivity conductor
• Increases current capacity by extending anode
service area
• Reduces anode consumption rate
• Extends anode life
• Common Brands: Loresco, Carbo-coke, Asbury

28. TYPES OF COKE BREEZE
The purpose of coke breeze is to create an electrical path
for current and to lower the overall resistivity of the
ground bed.
Metallurgical coke:
• Made from heating coal (500C
to 800C) without air contact.
• Low in Carbon content and
porous.
• 81% to 92% carbon, 50 ohm-
cm
• Relatively high in resistivity
• Typically used only with
conventional ground beds.
Petroleum coke:
• Made from heating Petroleum
residue
• Green Coke is heated to (950C
to 1200C) in a heat treating
vessel or calciner.
• 99% carbon, <10 ohm-cm
• Low in volatile material
• Higher in real bulk density
• Suitable for all types of
impressed current ground
beds.

29. COKE BREEZE FACTS
• Sizing of the carbon should be relatively small in comparison to the
anode diameter.
• Smaller particles ensure maximum electrical contact with the
anode.
• The shape of a carbon particle is directly related to its settling
characteristics.
• A spherical shaped carbon is desired for its decrease in surface
tension.
• Spherical carbons will settle more compacted.
• Spherical carbons will less likely trap gasses when compared to
irregular shaped particles
• A carbon with a high bulk density is desired due to electrical
conductivity.
• Carbon with a high bulk density will achieve a longer life.

30. Spherical Carbon Irregular Shaped Carbon
GRANULAR PICTURE OF COKE PARTICLES

31. CONDUCTIVE CONCRETE
• Requires specialized equipment
• Water ratio mix
• NSF 60 Rated
• 2800 psi-28 Days
• Very impermeable
• Low carbon consumption 1.1 #/yr/amp
• Requires no vent tube

32. ALL VENT PIPE
• Used to relieve gas from the
function of the ground bed.
• Pipe is perforated to allow the gas
into the pipe at multiple locations
in the active length of the anodes.
• Usually PVC pipe used after the
active column.
• The all vent perforation should be
within (0.006in to 0.009in) to
minimize debris.

33. HOLE PLUG
• Prevents contamination of underground water aquifers from
above ground liquids by sealing the hole.
• Easy installation does not require any outside tools or
equipment.
• When installed properly will completely seal off the hole.
• Approved for installation around potable drinking water.

34. QUESTIONS?
CHARLIE POORE
NACE Senior Corrosion Technologist #53904
Cell 505-250-7481
charlie.poore@mesaproducts.com