Cathodic Protection Testing ASTSWMO Louisville, KY

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

What is Cathodic protection?

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

Corrosion Cell Metallic Path Anode Electrolyte Cathode DC Current Flow

Galvanic Cathodic Protection

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

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

Sti-P3 Tank to Soil potential reading - 0.910 v Sti-P3 Tank to Soil potential reading TANK Connection to tank 30 ft

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

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

Always Use DC V

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.

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

Sti-P3 Tank to Soil potential - 0.910 v 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

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

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

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

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

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

Anything Unusual?

Anything Unusual?

Site Drawing

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

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

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

Reference Cell over tank Drill holes if necessary

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

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 -850. Piping readings missing.

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

Backfill in STP 945 mV 975 mV 932 mV

Backfill in ATG 945 mV 819 mV 964 mV 972 mV

Remote reading -948 mV

WHAT DOES THE REMOTE EARTH POTENTIAL MEASURE? May be thought of as representing the average potential over the entire tank 30-100 feet

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”)

RAISED EARTH RA I SED EARTH

PEA GRAVEL/CRUSHED STONE

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

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

“REMOTE”

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

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

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.

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

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

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

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

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

Look for Rectifier

Not always easy to see!

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

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

-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 -39.845 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.

IMPRESSED CURRENT TESTING PASS: -850 mV or more negative instant off or 100 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

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

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

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

-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 -39.845 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.

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

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

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

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

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

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

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

Example 3: Impressed Current Site Map CP Test

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.

Instant off is used – but what’s wrong?

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.

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 -1048 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.

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?

Possible Problems Lo Look for wires extruding through cracks

Impressed Current Site A

Impressed Current Site A

Impressed Current Site A

Impressed Current Site A 1 Reading 2 Readings

Impressed Current Site A 1 Structure 2 Structures

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

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.

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.

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

Example Remote reference cell reading Are these structures isolated? Tank A = -725 mV Tank B = -724 mV Tank C = -910 mV Are these structures isolated?

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

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

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

Flex connectors

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)

STI R972 STI Recommended Practice for the Addition of Supplemental Anodes Updated 2010 www.steeltank.com

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

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

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

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

Lorri Grainawi Director of Technical Services Steel Tank Institute Phone: (847) 550-3831 lgrainawi@steeltank.com www.steeltank.com