1. Cathodic Protection Testing
ASTSWMO
Louisville, KY

2. What we will cover Galvanic and Impressed Current Systems
Basic cathodic protection testing
How many readings and where to take them
Continuity testing
Understanding forms
ICCS
Verify current output, make sure there is current and it’s not declining to zero
Why Instant off readings
CP in sumps and flex connectors

3. What is Cathodic protection?

4. Relative Energy Levels of Metals
Measured relative to a Cu/CuSO reference cell
Anodic
Active (Corrodes Easily)
MAGNESIUM
-1600
ZINC
-1100
ALUMINUM
-1000
STEEL
- 600
COPPER
- 100
CARBON
+ 400
SILVER
+ 500
PLATINUM
+ 900
GOLD
1200
Passive (Stable)
Cathodic

5. Corrosion Cell
Metallic Path
Anode
Electrolyte
Cathode
DC Current Flow

6. Galvanic Cathodic Protection

7. What is an sti-P3 UST?
Pre-engineered factory fabricated cathodically protected steel tank with three modes of corrosion control
1 electrical isolation
2 external coatings
3 galvanic anodes
I am going to start with the basics. Here in Maine there are other types of cp tanks installed as well.
sti-P3

8. Corrosion Control
So if a buried steel tank is completely isolated (like a sti-P3 tank) why are we concerned about corrosion?
Steel is made up of many different “crystals”. Each of which could have a different potential reading.
The potential you measure is actually an average of all the steel “crystals” that make up a typical tank.
585 mV
600 mV
605 mV
615 mV

9. Sti-P3 Tank to Soil potential readingv
Sti-P3 Tank to Soil potential reading
TANK
Connection to tank
30 ft

10. Brief overview of how cathodic protection works
Brief overview of how cathodic protection works. We are simply making what naturally occurs work for us.

11. Testing Equipment Reference Cells Voltmeters Test Leads -850 V V A A
OFF
Reference Cells
Voltmeters
Test Leads V
300mV A A
10 A
V/OHM
300 mA
COM

12. Always Use
DC V

13. Correct scale?
If the meter reads “OL” (overload) or “1” then meter is on too low a scale and you need to switch to a higher scale.
If the meter reads 0 (zero) you have the meter on too high a scale and you need to switch to a lower scale.
Keep in mind that you always want to use the lowest scale possible to get the highest degree of resolution in the measurement.

14. Copper/Copper Sulphate Reference Cell
Use 99% pure Copper Sulphate crystals
Add distilled water or special antifreeze solution, about ¾ full, at least night before use
Crystals must be visible to know that solution is saturated and good for use
Reference cell liquid should be clear blue, not milky

15. Sti-P3 Tank to Soil potentialv
Sti-P3 Tank to Soil potential
Test Leads
Voltmeter
Reference Cell
Testing galvanic systems is very simple. All you need is a meter, a reference cell and enough wires to make your connections. Black to reference cell will always give you a negative reading. Consistency is important.
TANK
Connection to tank
30 ft

16. Documentatoin
This doesn’t cut it AND – it doesn’t make sense.

17. Reviewing CP Test Reports
What’s unit? V, mV, A?
Can’t rely on one reading
Numbers don’t make sense!

19. Testing Cathodic Protection
Good connection to tank is critical
Meter
Reference cell placement is everything 1.
3. Wire to Ref Cell 2.

20. Need good electrical connection to tank
Need good electrical connection to tank. Where you connect to tank does NOT matter.

21. Reference cell placement
Where you place the reference cell means everything
Where you touch the structure being tested means nothing, provided good electrical contact

22. Anything Unusual?

23. Anything Unusual?

24. Site Drawing

25. Tank to soil potential readings
DO place reference cell in moist soil/ backfill
DO NOT place reference cell in
Dry soil
Fuel contaminated soil
Frost or frozen soils
Vegetation (grass)
Concrete, asphalt or paving of any kind
Plastic lined flower beds

26. Summary of Test Procedure for sti-P3 Structure Potentials
Set meter to 2 Volt DC scale
Take the cap off the reference cell
Plug black lead into the negative terminal on multi-meter and clip to reference cell.
Place red lead into the positive terminal and clip to the structure under test.
Moving tank connection shouldn’t change potential reading!!
Place reference cell in remote earth

27. Summary of Test Procedure For sti-P3
Structure Potentials
Move reference cell 10 feet further away and verify reading is approximately the same.
Record the remote measurement and reference cell placement on site map.
Move reference cell to center of tank.
Now have 3 tank readings.
Record all measurements and reference cell placements on site map

28. Reference Cell over tank Drill holes if necessary

29. Example 2: Galvanic System w/ Metal Piping
Description
Isolation/Continuity Test
CP Test
Site Map

30. Example 2 (Contd): Galvanic System w/ Metal Piping
Isolation/Continuity Testing:
CP Testing:
Isolation/continuity testing shows that tank is isolated from piping. BUT: Why is remote for tank so low (less than -850)?
Local CP test readings are on tank only. Where is piping?.
Summary: This is an incomplete test – no local piping tested. I have questions as to why remote tank reading isn’t Piping readings missing.

31. WHAT DOES THE LOCAL POTENTIAL MEASURE?
“3 point test rule”
Burial depth = 2 feet
Tank diameter = 8 feet
Tank length = 24 feet
Only the top portion of tank is measured
Reference Cell radius of influence = 4 x height above structure 2 8 8 8 24 8

32. Backfill in STP
945 mV
975 mV
932 mV

33. Backfill in ATG
945 mV
819 mV
964 mV
972 mV

34. Remote reading
-948 mV

35. WHAT DOES THE REMOTE EARTH POTENTIAL MEASURE?
May be thought of as representing the average potential over the entire tank
feet

36. WHY MEASURE THE REMOTE?
Mitigate environmental factors that can influence test measurements over tank (“shielding”)
Eliminate influence nearby anodes can have on test measurements over tank (“raised earth”)

37. RAISED EARTH
RA I SED
EARTH

38. PEA GRAVEL/CRUSHED STONE

39. PEA GRAVEL/CRUSHED STONE
-525
-435
-590
Remote = -940

40. HOW DO YOU ESTABLISH REMOTE EARTH?
980mV
960mV
950mV
920mV
920mV
10’
20’
30’
40’
Keep moving reference cell away from tank until potential remains the same

41. “REMOTE”

42. Pass/Fail Criteria - Galvanic
PASS: mV or more ON readings for both local and remote readings. OR
PASS: -850 mV or more Instant Off readings for all recorded readings.

43. Testing Other Structures
When testing a galvanic cathodic protection system, you should test all metal structures that routinely contain product
Flex connectors
Metal product piping
Place reference cell away from anodes

45. TESTING FLEX CONNECTOR CP
If buried in ground - must test with reference cell both local and remote OR conduct instant off reading
Local means reference cell is in soil within man way or under dispenser
Local will be influenced by “raised earth” of active anodes
Unleaded sump close-up of metal flex pipe in contact with water and something on the flex pipe.

46. TESTING FLEX CONNECTOR CP
If contained within sump can only test locally
Sump will “shield” remote reference cell

47. TESTING FLEX CONNECTOR CP
Reference cell must be placed within water of sump
Do not completely submerge reference cell

48. Piping Test Test at “both ends” of pipe
One reading with reference cell at dispenser
One reading with reference cell at STP

49. Inspector Guidelines at Site with Cathodic Protection
Does the site have Galvanic or Impressed Current CP?

50. What do you see?
Dispensers
Tank Manways
But what type of CP?

51. Look for Rectifier

52. Not always easy to see!

53. Look for saw marks, line cuts or drill holes in concrete

54. TYPICAL RECTIFIER 1. Data Plate 1 2. On/Off Switch 2 3 3. Tap Settings
4. Fuse 4 5
5. Hour Meter
6. Amperage 7 6
7. Voltage 8
8. Shunt 10 9
9. Negative
10. Positive

56. -39.845 VDC Output Voltage Ø Turn the voltmeter to V DC
AMMETER
STRUCTURE
(-)
ANODE
(+)
COARSE SETTINGS
FINE SETTINGS 1 2 3 4 6 5 A B C D F E
Output Voltage
VDC
FLUKE 87
TRUE RMS MULTIMETER
PEAK MIN MAX
MIN MAX RANGE HOLD
)))))) REL Hz V mV
A mA uA COM VW W mA A uA
Ø Turn the voltmeter to V DC
Ø     Connect the black voltmeter test lead to the Anode (+) on the rectifier.
Ø     Connect the red voltmeter test lead to the Structure (-) on the rectifier.

57. IMPRESSED CURRENT TESTING
PASS: mV or more negative instant off or mV shift has been demonstrated at all local potential testing points
FAIL: Unable to obtain -850mV or 100 mV shift at one or more local testing points

58. IMPRESSED CURRENT TERMS
Native Potential - Potential measured before any CP has been applied
Static Potential – Also called the depolarized potential…it is measured after CP has been interrupted and structure is allowed to depolarize completely
Polarized Potential – Also called the instant off potential… the 2nd number observed on digital voltmeter after rectifier power has been interrupted

59. IMPRESSED CURRENT GENERALIZED TEST PROCEEDURE
Check operation of rectifier
Output Voltage/Amperage
Place reference cell in soil over tank/pipe
Record “on” potential
Temporarily interrupt rectifier power
Record “instant off” potential
Repeat as many times as needed
Conduct 100 mV polarization decay if needed
Establish continuity of all protected components

60. So what are we doing?
Check ammeter – is it within 10% of original value? Is it heading towards zero?
Check Tap settings – have they changed?
Check hour meter if present – has system been on?
Look for any broken wires

61. -39.845 VDC Output Voltage Ø Turn the voltmeter to V DC
AMMETER
STRUCTURE
(-)
ANODE
(+)
COARSE SETTINGS
FINE SETTINGS 1 2 3 4 6 5 A B C D F E
Output Voltage
VDC
FLUKE 87
TRUE RMS MULTIMETER
PEAK MIN MAX
MIN MAX RANGE HOLD
)))))) REL Hz V mV
A mA uA COM VW W mA A uA
Ø Turn the voltmeter to V DC
Ø     Connect the black voltmeter test lead to the Anode (+) on the rectifier.
Ø     Connect the red voltmeter test lead to the Structure (-) on the rectifier.

62. Test Procedure for ICCS
Structure Potentials
Place reference cell directly over center of tank, or as close as possible adding water to backfill as needed
Record “on” potential
Interrupt rectifier power and record instant off potential (without moving reference cell)
Move reference cell and record on/off potentials as many times as needed for tanks & pipes
If all “Ioff” potentials are more negative than -850 mV, you are done with potential survey

63. REFERENCE CELL LOCATIONS FOR TANK-TO-SOIL POTENTIALS
Place reference cell directly onto soil
Over or near the tank and piping
Maximize distance from anodes
Piping should be tested at both ends

64. Instant Off Readings
The instant off reading is the 2nd number that appears on the voltmeter after the rectifier is cut off
The 2nd number is used because of the way digital voltmeters capture/display data

65. WHY “INSTANT OFF”?
Any current flowing through a resistance creates a voltage drop
This voltage drop affects the reading you see - Making it appear more negative than it really is
If you turn the rectifier off - There is no current flowing and there is no voltage drop
In practical terms, the “On” potential does not mean anything

66. Test Procedure for ICCS
Structure Potentials
If one or more of the off potentials do not meet the -850 criterion, conduct 100 mV polarization decay
Place reference cell in spot where lowest (most positive) potential reading was observed and cut off rectifier.
Leave rectifier off until polarization has decayed at least 100 mV.
By doing this, you test the “worst-case” location first

67. Voltage Drop / Polarization Decay
RECTIFIER TURNED OFF AT THIS POINT
1000
ON = 950 mV
VOL TAGE
900
VOLTAGE
DROP = 250 mV
INSTANT OFF = 700 mV
800
700
POLARIZATION DECAY=125 mV
STATIC POTENTIAL =575 mV
600
TIME

68. IR DROP IN VOLTAGE MEASUREMENTS
Current flow through a resistor creates a voltage drop V R I
IR drop is more significant on impressed current systems as compared to galvanic systems

69. Example 3: Impressed Current
Site Map
CP Test

70. Example 3 (contd): Impressed Current
Site was not turned on when the tester arrive, so he recorded native potentials and then turned the system on. I’d guess he didn’t give it much time to polarize because of the lower on readings he appears to be getting.
Where are the instant off potentials?
Where are the continuity tests?
This person is measuring the difference between on and off and saying it meets 100 mV polarization.

71. Instant off is used – but what’s wrong?

72. V “instant off” – V “static” ≥ 100 mV
100 MV Shift
A tank meets the 100 mV shift criteria, if:
The tank is not connected to significant amounts of copper or stainless steel, and
The difference between the instant off potential and the static potential (depolarized potential) is at least 100 mV.
V “instant off” – V “static” ≥ 100 mV
The 100 mV shift criterion can be used on galvanic systems, but you must be able to disconnect the anodes.

73. Example 4: Impressed Current System
Here’s a real CP test record that an inspector in the North East shared with me. Do you see any problems with this? Is CP adequate here?
If I had to answer – I’d say that I don’t know. First, this tester appears to have used the change between system on and instant off for the “change” of 100 mV polarization. Second, the instant off is less than -850 mV. The “system on” potential is mV but how is IR drop accounted for? Finally, If I compare the instant off to the native information, I don’t always get more than 100 mV polarization. Also, this is only a single reading and I don’t know if components are isolated or connected.

74. All metallic structures buried in ground must be considered
Tanks & piping within 100’ are likely affected
If not part of design, tanks & piping can quickly leak
Other tanks at site?

75. Possible Problems Lo
Look for wires extruding through cracks

76. Impressed Current Site A

77. Impressed Current Site A

78. Impressed Current Site A

79. Impressed Current Site A
1 Reading
2 Readings

80. Impressed Current Site A
1 Structure
2 Structures

81. Continuity Testing
Structures that are galvanically protected must be isolated from other metallic structures
With Impressed Current systems, all structures are bonded together (continuous)
Continuity is critical for Impressed Current systems

82. Continuity Testing
Structures that are electrically isolated do not touch in any way
Structures that are electrically continuous are grounded to each other
sti-P3 tanks are designed to be electrically isolated from all other structures.

83. Nylon bushings
Nylon bushings utilized in all sti-P3 tank bungs to isolate the tank from any other metallic structure.
Tank hold down straps must be nonmetallic or isolated from tank shell.

84. METHODS TO TEST CONTINUITY
FIXED CELL MOVING GROUND
Reference cell is placed in remote soil at least 30 feet from all metallic structures
Measure the potentials of various structures within the facility with respect to the reference cell
Potential differences between measurements should be 1 mV or less to verify continuity
If 10 mV or greater = isolated
If > 1 mV but < 10 mV = inconclusive

85. Example Remote reference cell reading Are these structures isolated?
Tank A = -725 mV
Tank B = -724 mV
Tank C = mV
Are these structures isolated?

86. METHODS TO TEST CONTINUITY
POINT TO POINT METHOD
Reference cell is not used – voltmeter only
With ICCS rectifier must be turned off
Two structures of interest are contacted with voltmeter leads
Potential difference should be 1 mV or less to verify continuity
Potential difference should be 10 mV or greater to verify isolation
Readings > 1 mV and < 10 mV inconclusive

87. METHODS TO TEST CONTINUITY
POINT TO POINT METHOD
Turn off rectifier
Disconnect negative cable at rectifier
Use negative as one point
Stretch wire out and touch everything else you need to test continuity on.
Vent lines STP’s
Steel piping Water lines
Flex connectors Natural gas lines
Tank risers Conduits

88. Cathodic Protection Surveys
Surveys should be performed at approximately the same time of year each time a facility is tested in order to take out any seasonal fluctuations that might arise.
Very wet in the winter
Very dry in the summer

89. Flex connectors

92. Cathodic Protection Surveys
What happens if the system does not pass?
Further investigation/troubleshooting is usually needed
Galvanic – Current requirement test
sti-P3 guide for supplemental anodes
Add anodes (CP expert)
Impressed Current – Adjust rectifier (consult with CP expert)
- Install new rectifier (CP expert)
- Add anodes (CP expert)

93. STI R972 STI Recommended Practice for the Addition of Supplemental Anodes Updated 2010

94. Scope of R972
Main purpose is to provide a simple solution to bring sti-P3 tanks back to NACE criteria
Conservative RP that gives step-by-step directions to contractors for adding supplemental anodes
Provides option to hiring a CP Specialist

95. Scope Sti-P3 tanks that are not connected to impressed current systems
Soil resistivity up to 40,000 ohm cm
Current requirement up to 30 mA current
Does not address stray currents

96. 2010 R972 updates Isolation is not required, but should be identified
Anode and structural lead wires shall be brought to grade and installed in a test station. .
Test stations which permit IR drop compensated readings are required

97. Two Anode Configuration
grade
Top View
Side View
End View
Supplemental
Anodes

98. Lorri Grainawi Director of Technical Services Steel Tank Institute Phone: (847)