NACE Standard TM0101-2012 Item No. 21240

Standard Test Method Measurement Techniques Related to Criteria for Cathodic Protection of Underground Storage Tank Systems

This NACE Standard is being made available to you at no charge because it is incorporated by reference in the New York State Department of Environmental Conservation Part 613 of Title 6 of the Official Compilation of Codes, Rules and Regulations of the State of New York (NYCRR). For a list of NACE standards pertaining to pipeline integrity issues, please visit www.nace.org/Pipelines-Tanks-Underground-Systems/. NACE members are entitled to unlimited downloads of NACE standards, reports and conference papers for free as part of their member benefits. ___________________________________________________________________ NACE International is the world authority in corrosion prevention and control and is dedicated to protecting people, assets, and the environment from the effects of corrosion. NACE provides multiple industries with the resources to recognize, qualify, and quantify corrosion in a variety of application-oriented and industryspecific subjects through technical training and certification, conferences, standards, reports, and publications. Established in 1943, today NACE has more than 34,000 members in over 130 countries. Learn more about NACE at www.nace.org.

Revised 2012-03-10 Approved 2001-11-07 NACE International 1440 South Creek Drive Houston, TX 77084-4906 +1 281-228-6200 ISBN 1-57590-137-4  2012, NACE International

TM0101-2012

This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, whether he or she has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE International standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. NACE International assumes no responsibility for the interpretation or use of this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual volunteers. Users of this NACE International standard are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard. CAUTIONARY NOTICE: NACE standards are subject to periodic review, and may be revised or withdrawn at any time in accordance with NACE technical committee procedures. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication and subsequently from the date of each reaffirmation or revision. The user is cautioned to obtain the latest edition. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International FirstService Department, 1440 South Creek Dr., Houston, Texas 77084-4906 (telephone +1 281-228-6200).

NACE International

i

TM0101-2012

_________________________________________________________________________ Foreword This NACE International standard test method provides descriptions of the measurement techniques most commonly used on underground storage tank (UST) systems to determine whether a specific cathodic protection (CP) criterion has been complied with at a test site. This standard includes only those measurement techniques that relate to the criteria or special 1 conditions contained in NACE SP0285. The measurement techniques described in this standard require that measurements be made in the field. Because these measurements are obtained under widely varying circumstances of field conditions and tank design, this standard is not as prescriptive as those NACE standard test methods that use laboratory measurements. Instead, this standard gives the user latitude to make testing decisions in the field based on the technical facts available. This standard is intended for use by corrosion control personnel concerned with the external corrosion of UST systems or similar structures, including those used to contain oil, gas, and water. This standard was prepared by Task Group (TG) 209 (formerly Work Group T-10A-14b), and was revised by TG 364, “Testing of Cathodic Protection Systems of Underground Storage Tanks,” in 2012. TG 364 is administered by Specific Technology Group (STG) 35, “Pipelines, Tanks, and Well Casings,” and is sponsored by STG 05, “Cathodic/Anodic Protection.” The measurement techniques provided in this standard were compiled from information submitted by committee members and others with expertise on the subject. Variations or other techniques not included may be equally effective. This standard is issued by NACE under the auspices of STG 35.

In NACE standards, the terms shall, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual. The terms shall and must are used to state a requirement, and are considered mandatory. The term should is used to state something good and is recommended, but is not considered mandatory. The term may is used to state something considered optional.

_________________________________________________________________________

NACE International

i

TM0101-2012

_________________________________________________________________________

NACE International Standard Test Method Measurement Techniques Related to Criteria for Cathodic Protection of Underground Storage Tank Systems Contents 1. General ..........................................................................................................................................1 2. Definitions ......................................................................................................................................1 3. Safety Considerations ....................................................................................................................3 4. Instrumentation and Measurement Guidelines ..............................................................................3 5. Structure-to-Electrolyte Potential Measurements ...........................................................................5 6. Causes of Measurement Errors ........................................................................................... 9 7. Voltage Drops Other Than Across the Structure-to-Electrolyte Interface .....................................10 8. Test Method 1—Negative 850 mV Structure-to-Electrolyte Potential of Steel Underground Storage Tank Systems with Cathodic Protection Applied .........................................................11 9. Test Method 2—Negative 850 mV Polarized Structure-to-Electrolyte Potential of Steel Underground Storage Tank Systems ........................................................................................13 10. Test Method 3—100 mV Cathodic Polarization of Steel Underground Storage Tank Systems .15 11. Test Methods for Continuity Testing of Steel Underground Storage Tank Systems ..................20 12. Piping and Appurtenances .........................................................................................................22 13. Records .....................................................................................................................................23 References ......................................................................................................................................23 Bibliography .....................................................................................................................................23 Appendix A: Using CP Coupons to Determine the Adequacy of Cathodic Protection (Nonmandatory).........................................................................................................................24 Appendix B: Checklists for CP Systems (Nonmandatory)................................................................28 FIGURES: Figure 1: Instrument Connections ......................................................................................................5 Figure 2: Cathodic Polarization Curves............................................................................................15 TABLE: Table 1: Conversion of Other Potential Measurements to CSE Equivalents......................................6

_________________________________________________________________________

NACE International

i

TM0101-2012 _________________________________________________________________________ Section 1: General 1

1.1 This standard provides procedures to test compliance with the CP criteria presented in NACE SP0285 on UST systems. Included are instrumentation and general measurement guidelines, procedures for three commonly used test methods, practices for taking voltage drops into consideration and preventing incorrect data from being collected and used, and procedures for testing for electrical continuity between USTs and other metallic equipment. The use of CP coupons to determine the adequacy of CP is described in Appendix A (Nonmandatory). 1.2 The provisions of this test method shall be applied by personnel who have acquired, by education and related practical experience, knowledge of the principles of CP of UST systems. Such individuals, at a minimum, must either be NACE International certified CP Testers, NACE International CP Specialists, or individuals qualified by professional education and related practical experience. 1.3 A given test technique may be ineffective or only partially effective. Conditions that may cause this to occur include elevated temperatures, disbonded dielectric or thermally insulating coatings, shielding, bacterial attack, and unusual contaminants in the electrolyte. 1.4 Deviation from this test method may be warranted in specific situations if corrosion control personnel can demonstrate that adequate CP has been achieved.

_________________________________________________________________________ (1)

Section 2: Definitions

Anode: The electrode of an electrochemical cell at which oxidation occurs. (Electrons flow away from the anode in the external circuit. It is usually the electrode where corrosion occurs and metal ions enter solution.) Cable: A bound or sheathed group of insulated conductors. Cathode: The electrode of an electrochemical cell at which reduction is the principal reaction. (Electrons flow toward the cathode in the external circuit.) Cathodic Polarization: (1) The change of electrode potential caused by a cathodic current flowing across the electrode/electrolyte interface; (2) a forced active (negative) shift in electrode potential. (See Polarization.) Cathodic Protection: A technique to reduce the corrosion rate of a metal surface by making that surface the cathode of an electrochemical cell. Coating: (1) A liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid protective, decorative, or functional adherent film; (2) (in a more general sense) a thin layer of solid material on a surface that provides improved protective, decorative, or functional properties. Conductor: A bare or insulated material suitable for carrying electric current. Contact Resistance: The resistance in the measurement circuit present in the interface between a reference electrode and an electrolyte. Corrosion: The deterioration of a material, usually a metal, that results from a chemical or electrochemical reaction with its environment. Corrosion Potential (Ecorr): The potential of a corroding surface in an electrolyte measured under open-circuit conditions relative to a reference electrode. (Also known as Electrochemical Corrosion Potential, Free Corrosion Potential, and Open-Circuit Potential.)

(1)

Definitions in this section reflect common usage among practicing corrosion control personnel and apply specifically to how terms are used in this standard. As much as possible, these definitions are in accordance with those in NACE/ASTM G 193 (latest revision).2

NACE International

1

TM0101-2012 CP Coupon: A metal sample representing the UST at the test site, used for CP testing, and having a chemical composition approximating that of the UST. The CP coupon size should be small to avoid excessive current drain on the CP system. CP Criterion: A standard for assessment of the effectiveness of a CP system. Electrical Isolation: The condition of being electrically separated from other metallic structures or the environment. Electrode: A material that conducts electrons, is used to establish contact with an electrolyte, and through which current is transferred to or from an electrolyte. Electrode Potential: The potential of an electrode in an electrolyte as measured against a reference electrode. (The electrode potential does not include any resistance losses in potential in either the electrolyte or the external circuit. It represents the reversible work to move a unit of charge from the electrode surface through the electrolyte to the reference electrode.) Electrolyte: A chemical substance containing ions that migrate in an electric field. For the purposes of this standard, electrolyte refers to the soil or liquid adjacent to and in contact with a buried or submerged metallic UST system, including the moisture and other chemicals contained therein. Foreign Structure: Any metallic structure that is not intended as a part of a system under cathodic protection. Galvanic Anode: A metal that provides sacrificial protection to another metal that is more noble when electrically coupled in an electrolyte. This type of anode is the electron source in one type of cathodic protection. Groundbed: One or more anodes installed below the earth’s surface for the purpose of supplying cathodic protection current. Holiday: A discontinuity in a protective coating that exposes unprotected surface to the environment. Impressed Current: An electric current supplied by a device employing a power source that is external to the electrode system. (An example is direct current for cathodic protection.) Instant-Off Potential: The polarized half-cell potential of an electrode taken immediately after the cathodic protection current is stopped, which closely approximates the potential without IR drop (i.e., the polarized potential) when the current was on. Interference: Any electrical disturbance on a metallic structure as a result of stray current. “Off” or “On”: A condition whereby cathodic protection current is either turned off or on. Polarization: The change from the corrosion potential as a result of current flow across the electrode/electrolyte interface. Polarized Potential: (1) (general use) the potential across the electrode/electrolyte interface that is the sum of the corrosion potential and the applied polarization; (2) (cathodic protection use) the potential across the structure/electrolyte interface that is the sum of the corrosion potential and the cathodic polarization. Potential Gradient: A change in the potential with respect to distance, expressed in millivolts per unit of distance. Potentiometer: A device for the measurement of an electromotive force by comparison with a known potential difference. Protection Potential: The most noble potential at which pitting or crevice corrosion, or both, will not propagate in a specific environment. Reference Electrode: An electrode having a stable and reproducible potential, which is used in the measurement of other electrode potentials. Remote Earth: A location on the earth far enough from the affected structure that the soil potential gradients associated with currents entering the earth from the affected structure are insignificant. Shielding: (1) Protecting; protective cover against mechanical damage. (2) Preventing or diverting cathodic protection current from its natural path. Stray Current: Current flowing through paths other than the intended circuit.

2

NACE International

TM0101-2012 Structure: Tanks, piping, and associated equipment that may/may not be under the influence of a cathodic protection system. Structure-to-Electrolyte Potential: The potential difference between the surface of a buried or submerged metallic structure and the electrolyte that is measured with reference to an electrode in contact with the electrolyte. Test Lead: A wire or cable attached to a structure for connection of a test instrument to make cathodic protection potential or current measurements. Underground Storage Tank (UST) System: The equipment and facility constructed, maintained, or used for underground storage of products including tanks, piping, pumps, and appurtenances associated with filling, storage, and dispensing of the stored products. Voltage: An electromotive force or a difference in electrode potentials expressed in volts (V). Voltage Drop: The voltage across a resistance when current is applied in accordance with Ohm’s law. [also sometimes referred to as IR drop] 2

2

Wire: A slender rod or filament of drawn metal. In practice, the term is also used for smaller-gauge conductors (6 mm [0.009 in ] [No. 10 American Wire Gauge {AWG}] or smaller).

_________________________________________________________________________ Section 3: Safety Considerations 3.1 Personnel who install, adjust, repair, remove, or test impressed current CP equipment shall be knowledgeable and qualified in electrical safety precautions before work is begun. The following procedures shall be implemented when electrical measurements are made: 3.1.1 Use properly insulated test lead clips and terminals to avoid contact with an unanticipated high voltage (HV). Attach test clips one at a time using a single-hand technique for each connection. 3.1.2 Use caution when long test leads are extended near overhead high-voltage alternating current (HVAC) power lines, 3 which can induce hazardous voltages onto the test leads. Refer to NACE SP0177 for additional information about electrical safety. 3.1.3 Use caution when making tests at electrical isolation devices. Before proceeding with further tests, use appropriate voltage detection instruments or voltmeters with insulated test leads to determine whether hazardous voltages exist. 3.1.4 Avoid testing when thunderstorms are in the area. 3.1.5 Use caution when opening manways and when stringing test leads across streets, roads, and other locations subject to vehicular and pedestrian traffic. When conditions warrant, use appropriate barricades, flagging, and flag persons. 3.1.6 Before entering excavations and confined spaces, inspect these areas to determine whether they are safe. Inspections may include shoring requirements for excavations and testing for hazardous atmospheres in confined spaces. 3.1.7 Observe appropriate electrical codes and applicable safety regulations.

_________________________________________________________________________ Section 4: Instrumentation and Measurement Guidelines 4.1 Electrical measurements of CP systems require the proper selection and use of instruments. Instruments used to determine structure-to-electrolyte potential, voltage drop, potential difference, and similar measurements shall have appropriate voltage ranges. The user should know the capabilities and limitations of the equipment, follow the manufacturer’s instruction manual, and be skilled in the use of electrical instruments. Failure to select and use instruments correctly causes errors in CP measurements. 4.1.1 Analog instruments are usually specified in terms of input resistance or internal resistance. This is usually expressed as ohms/volt (Ω/V) of full-scale meter deflection.

NACE International

3

TM0101-2012 4.1.2 Digital instruments are usually specified in terms of input impedance expressed as megohms. 4.2 Factors that may influence instrument selection for field testing include: (a)

Input impedance (digital instruments);

(b)

Input resistance or internal resistance (analog instruments);

(c)

Sensitivity;

(d)

Conversion speed of analog-to-digital converters used in digital or data-logging instruments;

(e)

Accuracy;

(f)

Instrument resolution;

(g)

Ruggedness;

(h)

Alternating current (AC) and radio frequency (RF) signal rejection; and

(i)

Temperature and climate limitations.

4.2.1 Digital instruments are capable of measuring and processing voltage readings many times per second. Evaluation of the input waveform processing may be required if an instrument does not give consistent results. 4.2.2 Measurement of structure-to-electrolyte potentials on UST systems affected by dynamic stray currents may require the use of recording or analog instruments to improve measurement accuracy. Dynamic stray currents include those from electric railway systems and mining equipment. 4.3 Instrument Effects on Voltage Measurements 4.3.1 To measure structure-to-electrolyte potentials accurately, a digital voltmeter must have a high input impedance (high internal resistance for an analog instrument) compared with the total resistance of the measurement circuit. 4.3.1.1 A digital meter used to measure structure-to-electrolyte potentials should have an input impedance of 10 megohms or more. However, an instrument with a lower input impedance may produce valid data if circuit contact errors are considered. One means of making accurate measurements is to use a potentiometer circuit in an analog meter. 4.3.1.2 A voltmeter measures the potential across its terminals within its design accuracy. However, current flowing through the instrument creates measurement errors because of voltage drops that occur in all resistive components of a measurement circuit. 4.3.2 Some analog-to-digital converters used in digital and data-logging instruments operate so fast that the instrument may indicate only a portion of the input waveform and thus provide incorrect voltage indications. 4.3.3 Parallax errors on an analog instrument shall be minimized by viewing the needle perpendicular to the face of the instrument on the centerline projected from the needle point. 4.3.4 The effect of measurement circuit resistance errors may be evaluated using an instrument with two or more input impedances (internal resistance for analog instruments) and comparing the values measured using different input impedances. If the measured values are essentially identical, measurement circuit resistance errors are negligible. Corrections must be made if measured values are not essentially identical. Digital voltmeters that have a single input impedance shall not be used for indicating measurement circuit resistance errors. Alternative measurements may be made with a potentiometer or by using two digital voltmeters with different input impedance values. 4.3.5 Specialized equipment that uses various techniques to measure the impressed current waveform and calculate a structure-to-electrolyte potential free of voltage drop is available. This equipment may minimize problems resulting from spiking effects, drifting of interrupters, and current from other direct current (DC) sources. 4.4 Instrument Accuracy

4

NACE International

TM0101-2012 4.4.1 Instruments must be scheduled for periodic calibration to a certified standard. 4.4.2 Instruments shall be checked for accuracy before use by comparing measurements to a standard voltage cell, to another acceptable voltage source, or to another appropriate instrument that has been appropriately calibrated for accuracy.

_________________________________________________________________________ Section 5: Structure-to-Electrolyte Potential Measurements 5.1 Voltmeters used to measure AC voltage, DC voltage, or other electrical functions usually have one terminal designated “common” (COM). This terminal may be black in color or have a negative symbol (–). The positive terminal may be red in color or have a positive symbol (+). 5.1.1 The positive and negative symbols in the voltmeter display indicate the direction of the current flow through the instrument. For example, a positive value in the voltmeter display indicates current flowing from the positive terminal through the voltmeter to the negative terminal (see Figure 1[a]). 5.1.2 Usually, one voltmeter test lead is black and the other is red. The black test lead should be connected to the negative terminal of the voltmeter, and the red lead should be connected to the positive terminal. 5.2 The usual technique to determine the DC voltage across battery terminals, across a structure-to-electrolyte interface, or from another DC system is to connect the black test lead to the negative side of the circuit and the red test lead to the positive side of the circuit. When connected in this manner, an analog instrument needle moves in an upscale (clockwise) direction, indicating a positive value with respect to the negative terminal. A digital instrument connected in the same manner displays a digital value, preceded by a positive symbol or no symbol at all. In each situation, the measured voltage is positive with respect to the instrument’s negative terminal. (see Figure 1[a].) 5.3 Voltage measurements should be made using the lowest range on the instrument. For an analog instrument, the voltage measurement is more accurate when it is measured in the upper two-thirds of a range selected for a particular instrument. 5.4 The voltage difference between a reference electrode and the structure being tested shall be measured with a voltmeter. The reference electrode potential is normally positive with respect to the structure; conversely, the structure is negative with respect to the reference electrode. A structure-to-electrolyte potential shall be measured using a DC voltmeter having an appropriate input impedance (internal resistance for an analog instrument), voltage range(s), test leads, and a stable reference electrode, such as a saturated copper/copper sulfate electrode (CSE), silver/silver chloride (Ag/AgCl) electrode, or saturated potassium chloride (KCl) calomel reference electrode. The reference electrode can may be portable or one designed for permanent installation. Potential measurements taken using reference electrodes other than a CSE shall be converted to the CSE equivalents as shown in Table 1.

Table 1 Conversion of Other Potential Measurements to CSE Equivalents Reference Electrode Calomel Silver/silver chloride Zinc

Equivalent to –850 mV CSE –780 mV –800 mV +250 mV

Correction Add –70 mV Add –50 mV Add –1,100 mV

5.5.1 CSEs are usually used for measurements if the electrolyte is soil or fresh water; they are sometimes used for measurements in salt water. If a CSE is used in a high chloride environment, the stability (lack of contamination) of the CSE must be determined before the measurements may be considered valid. 5.5.2 The Ag/AgCl reference electrode is usually used in seawater environments. 5.5.3 The saturated KCl calomel reference electrode is used mainly for laboratory work. However, more rugged, polymer body, gel filled, saturated KCl calomel reference electrodes that are suitable for field work are available, though modifications may be necessary to increase their contact area with the environment.

NACE International

5

TM0101-2012 5.6 Meter Polarity 5.6.1 Structure-to-electrolyte potentials are often measured by connecting the negative terminal of the measuring instrument to the structure and the positive terminal to the reference electrode placed in the electrolyte, which is in contact with the structure. With this connection, the instrument indicates that the reference electrode is positive with respect to the structure. Therefore, the structure potential is negative with respect to the reference electrode (see Figure 1[a]). 5.6.2 Structure-to-electrolyte potentials are sometimes measured with the reference electrode connected to the instrument negative terminal and the structure connected to the positive terminal. This produces a negative voltage display on digital meters (see Figure 1[b]).

Voltmeters

+ 0.850 0

DC

1

Direction of meter current + -

VOLT

-

+

Reference Electrode

COM

-

+ Electrode potential

does notnot vary. does vary

TankTest TestLead Lead Pipe

C L Tank Pipe potential is the variable potential is Tank Pipe

the variable.

Figure 1(a): Conventional instrument connection.

6

NACE International

TM0101-2012

Voltmeter

- 0.850 DC

Direction of meter current + -

VOLT

Reference Electrode

COM

-

+ Electrode potential does not not vary. does vary

TankTest TestLead Lead Pipe

CL Tank potential Pipe potential is the is the variable variable. Tank Pipe

Figure 1(b): Alternative instrument connection. Figure 1: Instrument Connections 5.7 The structure-to-electrolyte potential measurement of a structure should be made with the reference electrode placed close to the structure-to-electrolyte interface. The most common practice on a UST, for example, is to place the reference electrode as close to the UST as practicable, which is usually at the surface of the earth above the centerline of the UST (see Figure 1). This measurement includes a combination of the voltage drops associated with the: (a)

Voltmeter;

(b)

Test leads;

(c)

Reference electrode;

(d)

Electrolyte;

(e)

Coating, if applied;

(f)

Structure-to-electrolyte interface; and

(g)

Reference electrode-to-electrolyte interface.

NOTE: A high input impedance (>10 megohm) voltmeter or potentiometer voltmeter should be used to eliminate the effects of Paragraph 5.7(a), (b), (c), (f), and (g) on the potential measurement. 5.8 The structure-to-electrolyte potential measurement is a result of the voltage drop created by current flowing through the electrical resistances of the items listed in Paragraph 5.7. For a coated UST, coating deterioration should be considered. 5.9 All measurements shall be taken with reference electrodes that are in contact with the electrolyte. Measurements shall not be taken through concrete or asphalt. Soil contact may be established through at-grade openings, by drilling a small hole through the concrete or asphalt, or by contacting a seam of soil between concrete and asphalt.

NACE International

7

TM0101-2012 5.10 The following conditions should be taken into consideration when structure-to-electrolyte potential measurements are made to determine the level of CP at the test site: (a)

Effectiveness of coatings, particularly those known or suspected to be deteriorated or damaged;

(b)

Uncoated sections of the UST system being cathodically protected;

(c)

Bonds to mitigate interference;

(d)

Parallel coated USTs, electrically connected and polarized to different potentials;

(e)

Shielding;

(f)

Effects of other structures on the measurements;

(g)

History of corrosion leaks and repairs;

(h)

Location and depth of anodes;

(i)

Existence of electrical isolation devices, including high-resistance pipe connections and compression couplings;

(j) Chemical composition of electrolytes, such as unusual corrosives, chemical spills, presence of hydrocarbons in soil, extreme soil resistivity changes, acidic waters, and contamination from sewer spills; (k) Possible sources of DC interference currents, such as welding equipment, foreign rectifiers, mining equipment, and electric railway or transit systems; (l)

Contacts with other metals or structures;

(m)

Areas of construction activity during the UST system history;

(n)

Underground metallic structures close to or crossing the UST system;

(o)

Other appurtenances; and

(p)

Electrolyte pH.

5.11 The effect of voltage drops other than those across the structure-to-electrolyte interface shall be considered for valid interpretation of structure-to-electrolyte potential measurements made to satisfy a criterion. Measurement errors should be minimized to ensure reliable structure-to-electrolyte potential measurements. 5.12 The primary method to determine the effect of voltage drops on a structure-to-electrolyte potential measurement is by interrupting all significant current sources before taking the potential measurement. This measurement must be taken without delay after the interruption of current to avoid loss of polarization. This measurement is referred to as an instant-off potential, and is considered to be the polarized potential of the structure at that location. This measurement does not account for voltage drops across the structure-to-electrolyte interface, which is part of the protection potential. NOTE: The current interruption may cause a voltage spike. This spike shall not be recorded as the instant-off potential. The magnitude and duration of the voltage spike can vary; however, the duration is usually within 0.5 second. 5.13 Examples of situations in which it may not be practical to interrupt all current sources to make the instant-off potential measurement include: 5.13.1 Galvanic anodes are connected directly to the structure without benefit of aboveground connections. Interruption of this kind of system requires excavation of the connections. 5.13.2 Interference from CP devices on foreign structure or electrical continuity with foreign structure. 5.13.3 Manmade sources of DC stray currents, such as other CP systems, mass transit, DC welding, or mining operations, are nearby.

8

NACE International

TM0101-2012 5.14 Significant environmental, structural, or CP system parameter changes may include: (a)

Replacement or addition of UST components and systems;

(b)

Addition, relocation, or deterioration of CP systems;

(c)

Failure of electrical isolation or bonding devices;

(d)

Changes in the effectiveness of coatings;

(e) (f)

Influence of foreign structures; and Modification of the environment.

5.15 After a CP system is operating, time may be required for the UST system to polarize. This should be taken into consideration when the potential at a test site on a newly protected UST system is measured or after a CP device is re-energized.

_________________________________________________________________________ Section 6: Causes of Measurement Errors 6.1 The following factors may contribute to faulty potential measurements: 6.1.1 UST system and instrument test leads (a)

Broken or frayed wire strands (may not be visible inside insulation of the wire);

(b) Damaged or defective test lead insulation that allows the conductor to contact wet vegetation, the electrolyte, or other objects; (c)

Loose, broken, or faulty UST system or instrument connections; and

(d)

Dirty or corroded connection points.

6.1.2 Reference electrode condition and placement (a) Contaminated reference electrode solution or rod, or solutions of insufficient quantity or saturation (only laboratory grade chemicals and distilled water, if water is required, should be used in a reference electrode); (b)

Reference electrode plug not sufficiently porous to provide a conductive contact to the electrolyte;

(c)

Porous plug contaminated by asphalt, oil, or other foreign materials;

(d) High-resistance contact between reference electrode and dry or frozen soil, rock, gravel, vegetation, or paving material; (e) Reference electrode placed in the potential gradient of an anode without consideration of the voltage drop caused by the anode, including reference electrode placement over the top of the structure(s) protected by close anodes; (f) Reference electrode positioned in the potential gradient of a metallic structure other than the one whose potential is being measured without consideration of the voltage drop caused by the potential gradient of the metallic structure; (g) Electrolyte between structure and disbonded coating causing error because of electrode placement in electrolyte on opposite side of coating; (h)

Defective permanently installed reference electrode;

(i)

Temperature correction not applied when needed;

(j) Photosensitive measurement error (in CSE with a clear-view window) caused by light striking the electrode electrolyte solution (photovoltaic effect); and

NACE International

9

TM0101-2012 (k)

Remote reference electrode placement in which voltage drops are not considered as part of the measurement.

6.1.3 Unknown electrical isolation devices, such as disbonded tubing or pipe systems, may cause the UST system to be electrically discontinuous between the test connection and the reference electrode location. (Section 11 provides guidance on methods of troubleshooting that identify continuity or discontinuity.) 6.1.4 Parallel paths may be inadvertently established by test personnel contacting instrument terminals or metallic parts of the test lead circuit, such as test lead clips and reference electrodes, while a potential measurement is being made. 6.1.5 The use of defective or inappropriate instruments, incorrect voltage range selection, instruments not calibrated or zeroed, or damp instruments sitting on wet earth may cause measurement errors. 6.1.6 Instruments that have an analog-to-digital converter may operate at such fast speeds that the voltage spikes produced by current interruption are indicated as the potential measurement instead of the actual “on” and “off” values. 6.1.7 The polarity of the measured value may be incorrectly observed. 6.1.8 Measurement errors may occur if the conductor carrying the CP current is used as a test lead for a UST system potential measurement. 6.1.9 Electromagnetic interference or induction resulting from AC power lines or RF transmitters can may induce test lead and instrument errors. This condition is often indicated by a fuzzy, fluctuating, or blurred pointer movement on an analog instrument or erratic displays on digital voltmeters. For this reason, DC voltmeters must have sufficient AC rejection capability, which may be determined by referring to the manufacturer’s specification. 6.1.10 The use of an internal UST connection via the fill pipe in the absence of a CP test wire when the UST has been lined may cause faulty potential measurements. 6.2 Several methods may be used to reduce contact resistance caused by the following factors: 6.2.1 Soil moisture: If the surface soil is so dry that the electrical contact of the reference electrode with the electrolyte is impaired, the soil around the electrode may be moistened with water until the contact is adequate. 6.2.2 Contact surface area: Contact resistance may be reduced by using a reference electrode with a larger contact surface area. 6.2.3 Frozen soil: Contact resistance may be reduced by removing the frozen soil to permit electrode contact with unfrozen soil. 6.2.4 Concrete or asphalt paved areas: Contact resistance may be reduced by drilling through the paving to permit electrode contact with the soil.

_________________________________________________________________________ Section 7: Voltage Drops Other Than Across the Structure-to-Electrolyte Interface Voltage drops present when structure-to-electrolyte potential measurements are made may occur in the following: 7.1 Measurement Circuit 7.1.1 The voltage drop other than across the structure-to-electrolyte interface in the measurement circuit is the sum of the individual voltage drops caused by the meter current flow through: (a) Instrument test lead and connection resistances; (b) Reference electrode internal resistance; (c) Reference electrode-to-electrolyte contact resistance; (d) Coating resistance;

10

NACE International

TM0101-2012 (e) Structure metallic resistance; (f)

Electrolyte resistance;

(g) Analog meter internal resistance; and (h) Digital meter internal impedance. 7.1.2 A measurement error occurs if the analog meter internal resistance or the digital meter internal impedance is not several orders of magnitude higher than the sum of the other resistances in the measurement circuit. 7.2 Electrolyte 7.2.1 When a structure-to-electrolyte potential is measured with CP current applied, the voltage drop in the electrolyte between the reference electrode and the structure-to-electrolyte interface shall be considered. Measurements taken close to sacrificial or impressed current anodes may contain a large voltage drop. 7.2.2 Such a voltage drop may consist of, but is not limited to, the following: (a) A voltage drop caused by current flowing to coating holidays when the UST system is coated; and (b) A voltage drop caused by large voltage gradients in the electrolyte that occur near operating anodes (sometimes called raised earth effect). 7.2.3 Testing to locate anodes by moving the reference electrode along the UST may be necessary when the locations are not known. 7.3 Coatings 7.3.1 Most coatings provide protection to the UST system by reducing contact between the UST system surface and the environment. While the insulation provided by a coating reduces the current required for CP of a coated UST system versus that required for an uncoated UST system, coatings are not impervious to current flow. 7.3.2 Coatings resist current flow because of their relative ionic impermeability. Current flow through the resistance of the coating causes the voltage drop to be greater than that occurring when the UST system is bare, under the same environmental conditions.

_________________________________________________________________________ Section 8: Test Method 1—Negative 850 mV Structure-to-Electrolyte Potential of Steel Underground Storage Tank Systems with Cathodic Protection Applied 8.1 This section describes a test method to satisfy the –850 mV with CP applied criterion stated in NACE SP0285. This section should be used for factory-installed galvanic anode CP systems in which the anodes cannot be disconnected. 8.1.1 Voltage drop must be considered when using this CP criterion. 8.1.2 The primary method for considering voltage drop(s) shall be by taking instant-off potential measurements in accordance with Sections 9 and 10. When anodes cannot be disconnected, other methods such as the following may be used: (a) Measuring or calculating the voltage drop(s); (b) Reviewing the historical performance of the CP system; (c) Evaluating the physical and electrical characteristics of the UST system and its environment; (d) Determining whether there is physical evidence of corrosion; and

NACE International

11

TM0101-2012 (e) Recording measurements with reference electrode placed electrically remote from the UST system (i.e., remote earth) in conjunction with local measurements. 8.2 General 8.2.1 Test Method 1 measures the structure-to-electrolyte potential as the sum of the polarized potential and any voltage drops in the circuit. These voltage drops include those through the electrolyte and structure coating from current sources such as impressed current and galvanic anodes. 8.2.2 CP current shall remain on during the measurement process. This potential is commonly referred to as the on potential. 8.2.3 Because voltage drops other than those across the structure-to-electrolyte interface may be included in this measurement, these voltage drops shall be considered, as discussed in Paragraph 8.6. 8.3 Comparison with Other Methods 8.3.1 Advantages (a) Requires minimal equipment, and (b) Less time is required to make measurements. 8.3.2 Disadvantages (a) The potential measured includes voltage drops other than those across the structure-to-electrolyte interface; (b) Meeting the requirements for considering the significance of voltage drops (see Paragraph 8.6) may result in a need for additional time to assess adequacy of CP at the test site; and (c) Test results are difficult or impossible to analyze if stray currents are present or foreign impressed current devices are present and cannot be interrupted. 8.4 Basic Test Equipment 8.4.1 A voltmeter with adequate input impedance. Commonly used digital instruments have a nominal impedance of 10 megohms. An analog instrument with an internal resistance of 100,000 ohms per volt may be adequate in certain circumstances in which the circuit resistance is low. A potentiometer circuit may be necessary in other instances. 8.4.2 Meter leads with insulated wire and terminal connections suitable for making reliable electrical contact with the structure and reference electrode. Color-coded meter leads should be used to avoid confusion of polarity for the measured value. 8.4.3 A CSE or other standard reference electrode may be used. Reference electrodes that may be used in place of a CSE are described in Paragraph 5.5. 8.5 The following procedure shall be followed when this test is performed: 8.5.1 Before the test, verify that CP equipment has been installed and is operating properly. Sufficient time should be allowed for the structure potentials to reach polarized values. 8.5.2 Determine the location of reference electrode placement for potential measurements. Selection of a site may be based on: (a) Accessibility for future monitoring; (b) Other protection systems, structures, and anodes that may influence the structure-to-electrolyte potential; (c) Electrical midpoints between protective devices; (d) Known location of an ineffective coating if the structure is coated; and

12

NACE International

TM0101-2012 (e) Location of a known or suspected corrosive environment. 8.5.3 Make electrical contact between the reference electrode and the electrolyte at the test site, in a location that minimizes the voltage gradient from anodes, other structures, and coating defects (if the structure is coated). 8.5.3.1 For factory-installed galvanic anode CP systems in which the anodes cannot be disconnected, a minimum of one local potential measurement near the UST center and away from the anodes and one remote potential measurement should be taken. Alternatively, a minimum of three potential measurements, one at each of the UST ends and one near the center of the UST, may be taken. 8.5.3.2 In general, the reference electrode should be placed as close to the UST surface as possible and as far from anodes as possible. 8.5.4 Record the location of the reference electrode to allow it to be returned to the same location for subsequent tests. 8.5.5 Connect the voltmeter to the structure and reference electrode as described in Paragraph 5.6. 8.5.6 Evaluate the effect of measurement circuit resistance on the structure-to-electrolyte potential as indicated in Paragraph 5.7. 8.5.7 Record the structure-to-electrolyte potential and its polarity with respect to the reference electrode. 8.5.8 Record a sufficient number of potential measurements to determine the level of CP over the entire structure. 8.6 Evaluation of Data 8.6.1 The significance of voltage drops may be considered by comparing historical levels of CP with physical evidence from the UST system to determine whether corrosion has occurred. 8.6.2 Physical evidence of corrosion may be determined by evaluating items such as leak history data or UST system inspection report data regarding locations of coating failures, localized conditions of more corrosive electrolyte, or whether substandard CP levels have been experienced. 8.6.3 The cathodic protection shall meet the –850 mV polarized criterion stated in NACE SP0285.

_________________________________________________________________________ Section 9: Test Method 2—Negative 850 mV Polarized Structure-to-Electrolyte Potential of Steel Underground Storage Tank Systems 9.1 This section describes a method that uses an interrupter(s) to eliminate the CP system voltage drop from the structure-toelectrolyte potential measurement for comparison with the CP criterion stated in NACE SP0285. 9.1.1 If directly connected galvanic anodes that cannot be interrupted are present, this test method shall not be used. 9.1.2 For impressed current CP systems, the tester must take instant-off potential measurements, unless a NACE Corrosion Specialist or NACE CP Specialist has determined that instant-off potential measurements are not required. 9.2 General 9.2.1 Interrupting the known CP current source(s) eliminates voltage drops associated with the protective currents. However, significant voltage drops may also occur because of currents from other sources. 9.2.2 Current sources that may affect the accuracy of this test method include the following: (a) Unknown, inaccessible, or directly connected galvanic anodes; (b) Other CP systems on associated piping or foreign structures; (c) Electric railway systems;

NACE International

13

TM0101-2012 (d) Galvanic or bimetallic cells; (e) DC mining equipment; (f) Adjacent tanks, electrically connected and polarized to different potentials; and (g) Unintentional connections to other structures or bonds to mitigate interference. 9.2.3 To avoid significant depolarization of the UST system, the “off” period should be limited to the time necessary to make an accurate potential measurement. The “off” period is typically less than three seconds. 9.3 Comparison with Other Methods 9.3.1 Advantages Voltage drops associated with the protective currents being interrupted are eliminated. 9.3.2 Disadvantages (a) Additional equipment is required; (b) Additional time may be required to set up equipment and to make structure-to-electrolyte potential measurements; and (c) Test results are difficult or impossible to analyze with regard to whether stray currents are present or foreign impressed current devices are present and cannot be interrupted. 9.4 Basic Test Equipment 9.4.1 A voltmeter with adequate input impedance. Commonly used digital instruments have a nominal impedance of 10 megohms. An analog instrument with an internal resistance of 100,000 ohms per volt may be adequate in certain circumstances in which the circuit resistance is low. A potentiometer circuit may be necessary in other instances. 9.4.2 Meter leads with insulated wire and terminal connections suitable for making reliable electrical contact with the structure and reference electrode. Color-coded meter leads should be used to avoid confusion of polarity of the measured value. 9.4.3 A CSE or other standard reference electrode may be used. Reference electrodes that may be substituted for the CSE are described in Paragraph 5.5. 9.4.4 Sufficient and adequate means to interrupt CP current sources (such as sacrificial anodes, rectifiers, and electrical bonds) that are influencing the structure simultaneously. 9.5 The following procedure shall be followed when this test is performed. 9.5.1 Before the test, verify that CP equipment has been installed and is operating properly. Sufficient time should be allowed for the UST system potentials to reach polarized values. 9.5.2 Install and place in operation necessary interrupter equipment in all DC sources influencing the UST system at the test site. The off interval should be kept as short as possible but still long enough to measure a polarized structure-to-electrolyte potential after any spike (see Figure 2[a]) has collapsed. 9.5.3 Determine the location of reference electrode placement for potential measurements. Selection of a site may be based on: (a) Accessibility for future monitoring; (b) Other protection systems, structures, and anodes that may influence the structure-to-electrolyte potential; (c) Electrical midpoints between protective devices;

14

NACE International

TM0101-2012 (d) Known location of an ineffective coating if the structure is coated; and (e) Location of a known or suspected corrosive environment. 9.5.4 Make electrical contact between the reference electrode and the electrolyte at the test site, in a location that minimizes the voltage gradient from other structures and coating defects (if the structure is coated). 9.5.5 Record the location of the reference electrode to allow it to be returned to the same location for subsequent tests. 9.5.6 Connect the voltmeter to the tank and reference electrode as described in Paragraph 5.6. 9.5.6.1 If spiking could be present, delay measurement of the tank-to-electrolyte potential to eliminate the voltage spike from the measured value. Spiking usually occurs within 0.5 second of the interruption of the CP currents. 9.5.6.2 Appropriate instrumentation such as an oscilloscope or high-speed recording device may be used to verify the presence and duration of the spiking. 9.5.7 Evaluate the effect of measurement circuit resistance on the structure-to-electrolyte potential as indicated in Paragraph 5.7. 9.5.8 Record the structure-to-electrolyte “on” and instant-off potentials and their polarities with respect to the reference electrode. 9.5.9 Record a sufficient number of potential measurements to determine the level of CP over the entire UST system. 9.6 Evaluation of Data CP shall be judged adequate at the test site if the polarized (instant-off) structure-to-electrolyte potential meets the CP criterion stated in NACE SP0285.

_________________________________________________________________________ Section 10: Test Method 3—100 mV Cathodic Polarization of Steel Underground Storage Tank Systems 10.1 This section describes the use of either polarization decay or polarization formation to determine whether the UST system CP is adequate at the test site in accordance with the 100 mV cathodic polarization criterion. Consequently, this test method consists of two mutually independent parts, Test Methods 3a and 3b, which describe the procedures for polarization decay and polarization formation testing, respectively. Generic cathodic polarization curves for Test Methods 3a and 3b are shown in Figure 2. Figure 2 contains schematic drawings of generic polarization decay and polarization formation. If directly connected galvanic anodes that cannot be interrupted are present, these test methods shall not be used.

NACE International

15

TM0101-2012

Pipe-to-Electrolyte Potential (-mV)

1,100

"On" Potential

1,000 0

Voltage Drop (IR Drop)

"Instant-Off" Potential (Polarized Potential)

Polarization Decay Depolarizing Line

Spike

Time Period (May be seconds, minutes, hours, or days)

Figure 2(a): Polarization decay

1,200 Current Interruption

Pipe-to-Electrolyte Potential (-mV)

1,100

Polarizing Line

Normal Operation "On" Potential

1,000

"Instant-Off" Potential Polarization

Cathodic Protection Applied Corrosion Potential

Time Period (May be seconds, minutes, hours, or days)

Figure 2(b): Polarization Formation Figure 2: Cathodic polarization curves.

16

Figure 3b Polarization Formation

NACE International

TM0101-2012 10.2 Test Method 3a—Use of Polarization Decay (See Figure 2[a]) 10.2.1 This test method uses polarization decay to assess the adequacy of CP of a steel UST system in accordance with the cathodic polarization criterion stated in NACE SP0285. 10.2.2 General 10.2.2.1 Interrupting the known CP source(s) eliminates voltage drops associated with the protective current(s). 10.2.2.2 Other current sources that may affect the accuracy of this test method include the following: (a) Unknown, inaccessible, or directly connected galvanic anodes; (b) CP systems on associated tank systems or foreign structures; (c) Electric railway systems; (d) Galvanic, or bimetallic, cells; (e) DC mining equipment; (f)

Adjacent tanks, electrically connected and polarized to different potentials;

(g) Unintentional connections to other structures or bonds to mitigate interference; and (h) C welding equipment. 10.2.3 Comparison with Other Methods 10.2.3.1 Advantages (a) This method is especially useful for bare or ineffectively coated tanks; and (b) This method is advantageous in places where corrosion potentials may be low (for example, 500 mV or less negative) or the current required to meet a negative 850 mV polarized potential criterion would be considered excessive. 10.2.3.2 Disadvantages (a) Additional equipment is required; (b) Additional time may be required to set up equipment and to make tank-to-electrolyte potential measurements; and (c) Test results are difficult or impossible to analyze if foreign impressed current devices are present and cannot be interrupted or if stray currents are present. 10.2.4 Basic Test Equipment 10.2.4.1 A voltmeter with adequate input impedance. Commonly used digital instruments have a nominal impedance of 10 megohms. An analog instrument with an internal resistance of 100,000 ohms/volt may be adequate in certain circumstances in which the circuit resistance is low. A potentiometer circuit may be necessary in other instances. Recording voltmeters may be useful for recording polarization decay. 10.2.4.2 Meter leads with insulated wire and terminal connections suitable for making reliable electrical contact with the structure and reference electrode. Color-coded meter leads should be used to avoid confusion of polarity of the measured value. 10.2.4.3 Sufficient and adequate means to interrupt CP current sources (such as sacrificial anodes, rectifiers, and electrical bonds) that are influencing the UST system simultaneously.

NACE International

17

TM0101-2012 10.2.4.4 A CSE or other standard reference electrode may be used. Reference electrodes that may be substituted for the CSE are described in Paragraph 5.5. 10.2.5 The following procedure shall be used when this test is performed: 10.2.5.1 Before the test, verify that CP equipment has been installed and is operating properly. Sufficient time should be allowed for the UST system potentials to reach polarized values. 10.2.5.2 Provide means for current interruption in all DC sources influencing the UST system at the test site. The “off” interval should be kept as short as possible but still long enough to measure a polarized structure-to-electrolyte potential after any spike (see Figure 2a) has collapsed. 10.2.5.3 Determine the location of reference electrode placement for potential measurements. Selection of a site may be based on: (a) Location accessible for future monitoring; (b) Other protection systems, structures, and anodes that may influence the structure-to-electrolyte potential; (c) Electrical midpoints between protective devices; (d) Known location of an ineffective coating if the UST system is coated; and (e) Location of a known or suspected corrosive environment. 10.2.5.4 Make electrical contact between the reference electrode and the electrolyte at the test site in a location that minimizes the voltage gradient from other structures and coating defects (if the UST system is coated). 10.2.5.5 Record the location of the reference electrode to allow it to be returned to the same location for subsequent tests. 10.2.5.6 Connect the voltmeter to the UST system and reference electrode as described in Paragraph 5.6. If spiking could be present, use an appropriate instrument, such as an oscilloscope or high-speed recording device, to verify that the measured values are not influenced by a voltage spike. 10.2.5.7 Measure and record the structure-to-electrolyte “on” and instant-off potentials and their polarities with respect to the reference electrode. The instant-off structure-to-electrolyte potential is the baseline potential from which the polarization decay is calculated. 10.2.5.8 Turn off the CP current sources that influence the UST system (i.e., those interrupted in Paragraph 10.2.5.2) at the test site. Continue to measure and record the structure-to-electrolyte potential until it either: (a) Becomes at least 100 mV less negative than the instant-off potential, or (b) Reaches a stable depolarized level. 10.2.5.8.1 Measurements shall be made at sufficiently frequent intervals to avoid attaining and remaining at a corrosion potential for an unnecessarily extended period. 10.2.5.8.2 If extended polarization decay time periods are anticipated, it may be desirable to use recording voltmeters to determine when adequate polarization decay or a corrosion potential has been attained. 10.2.5.9 Record a sufficient number of potential measurements to determine the level of CP over the entire UST system. 10.2.6 Evaluation of Data The CP shall meet the 100 mV cathodic polarization criterion stated in NACE SP0285. 10.2.7 Monitoring

18

NACE International

TM0101-2012 When at least 100 mV or more of polarization decay has been measured, the UST system “on” potential at the test site may be used for monitoring unless significant environmental, structural, coating integrity, or CP system parameters have changed. 10.3 Test Method 3b—Use of Polarization Formation (See Figure 2[b]) 10.3.1 This test method provides a procedure using the formation of polarization to assess the adequacy of CP at a test site on a steel UST system in accordance with the cathodic polarization criterion stated in NACE SP0285. 10.3.2 General 10.3.2.1 Steel UST systems may be adequately protected if, from the “off” potential, applying CP causes a polarized potential that is at least 100 mV more negative. 10.3.2.2 Current sources that may affect the accuracy of this test method include the following: (a) Unknown, inaccessible, or directly connected galvanic anodes; (b) CP systems on associated tank systems or foreign structures; (c) Electric railway systems; (d) Galvanic, or bimetallic, cells; (e) DC mining equipment; (f)

Adjacent tanks, electrically connected and polarized to different potentials;

(g) Unintentional connections to other structures or bonds to mitigate interference; and (h) DC welding equipment. 10.3.3 Comparison with Other Methods 10.3.3.1 Advantages (a) This method is especially useful for a bare or ineffectively coated UST system; and (b) This method is advantageous if corrosion potentials could be low (for example, 500 mV or less negative) or the current required to meet a negative 850 mV potential criterion would be considered excessive. 10.3.3.2 Disadvantages (a) Additional equipment is required; (b) Additional time may be required to set up equipment and to make the structure-to-electrolyte potential measurements; and (c) Test results are difficult or impossible to analyze if foreign impressed currents are present and cannot be interrupted or if stray currents are present. 10.3.4 Basic Test Equipment 10.3.4.1 A voltmeter with adequate input impedance. Commonly used digital instruments have a nominal impedance of 10 megohms. An analog instrument with an internal resistance of 100,000 ohms/volt may be adequate in certain circumstances in which the circuit resistance is low. A potentiometer circuit may be necessary in other instances. 10.3.4.2 Meter leads with insulated wire and terminal connections suitable for making reliable electrical contact with the structure and reference electrode. Color-coded meter leads should be used to avoid confusion of polarity of the measured value.

NACE International

19

TM0101-2012 10.3.4.3 Sufficient and adequate means to interrupt CP current sources (such as sacrificial anodes, rectifiers, and electrical bonds) that are influencing the tank simultaneously. 10.3.4.4 A CSE or other standard reference electrode may be used. Reference electrodes that can be substituted for the CSE are described in Paragraph 5.5. 10.3.5 The following procedure shall be used when this test is performed: 10.3.5.1 Before the test, verify that CP equipment has been installed but is not operating. 10.3.5.2 Determine the location of reference electrode placement for potential measurements. Selection of a site may be based on: (a) Location accessible for future monitoring; (b) Other protection systems, structures, and anodes that may influence the structure-to-electrolyte potential; (c) Electrical midpoints between protective devices; (d) Known location of an ineffective coating if the UST system is coated; and (e) Location of a known or suspected corrosive environment. 10.3.5.3 Make electrical contact between the reference electrode and the electrolyte at the test site in a location that minimizes the voltage gradient from other structures and coating defects (if the UST system is coated). 10.3.5.4 Record the location of the reference electrode to allow it to be returned to the same location for subsequent tests. 10.3.5.5 Connect the voltmeter to the structure and reference electrode as described in Paragraph 5.6. 10.3.5.6 Measure and record the structure-to-electrolyte potential and its polarity with respect to the reference electrode. This potential shall be the value from which the polarization formation is calculated. 10.3.5.7 Apply the CP current. Sufficient time should be allowed for the UST system potentials to reach polarized values. 10.3.5.8 Install and place in operation necessary interrupter equipment in the DC sources influencing the UST system at the test site. The “off” interval should be kept as short as possible but still long enough to measure a polarized structureto-electrolyte potential after any spike (see Figure 2[a]) has collapsed. 10.3.5.9 Measure and record the structure-to-electrolyte “on” and instant-off potentials and their polarities with respect to the reference electrode. The difference between the instant-off potential and the original potential is the amount of polarization formation. 10.3.5.9.1 If spiking may be present, delay measurement of the structure-to-electrolyte potential to eliminate the spike voltages from the measured value. Spiking usually occurs within 0.5 second of the interruption of the CP currents. 10.3.5.9.2 Appropriate instrumentation such as an oscilloscope or high-speed recording device may be used to verify the presence and duration of the spiking. 10.3.5.10 Record a sufficient number of potential measurements to determine the level of CP over the entire UST system. 10.3.6 Evaluation of Data The CP shall meet the 100 mV cathodic polarization criterion stated in NACE SP0285. 10.3.7 Monitoring

20

NACE International

TM0101-2012 When at least 100 mV or more of polarization formation has been measured, the structure on potential may be used for monitoring unless significant environmental, structural, coating integrity, or CP system parameters have changed.

_________________________________________________________________________ Section 11: Test Methods for Continuity Testing of Steel Underground Storage Tank Systems 11.1 The following test methods may be used to determine whether a tank is electrically continuous with piping, electrical equipment, conduit, and other appurtenances or structures in the immediate area. This list of tests is not all-inclusive. Other methods or equipment may be used to test for electrical continuity or discontinuity. 11.2 UST systems may have been designed to be electrically isolated from other metallic structures such as piping, conduit, grounded electrical equipment, and hold-down devices. A lack of electrical isolation from these structures can result in lowered levels of CP or a reduction in the life of the CP system. 11.2.1 Some UST systems are designed to have electrical continuity between the UST and the related piping, electrical equipment, and other appurtenances or accessories. Discontinuity between the UST and another structure or appurtenance can result in a lack of protection, and in some cases, damage to the UST or appurtenances that are isolated. 11.2.2 One method to verify the continuity of the negative bond wire to the intended structure(s) being protected is to disconnect the negative lead wire from the rectifier and connecting one lead of the voltmeter to this negative lead wire and measuring the potential difference between the negative lead wire and other structures. 11.3 Fixed Cell/Moving Ground Technique 11.3.1 This technique uses basic CP test equipment to test for an indication of possible electrical continuity through the use of structure-to-electrolyte potential comparison measurements. 11.3.2 The following procedure shall be followed when testing for continuity using the fixed cell/moving ground technique: 11.3.2.1 Make electrical contact between the reference electrode and the electrolyte at a location remote from the UST system to be tested. 11.3.2.1.1 The location should not be within the potential gradient of an anode or any other structure. Placement of the reference electrode in a location that is shielded by another tank or structure may result in erroneous data concerning the continuity of the shielded tank(s) or structures. Alternate reference electrode placements may be necessary to determine the continuity of all of the structures at a test site. 11.3.2.1.2 Once placed, the reference electrode shall not be moved for the duration of this test procedure. 11.3.2.2 Connect the voltmeter to the structure. 11.3.2.3 Measure and record the structure-to-electrolyte potential with respect to the reference electrode. 11.3.2.4 Disconnect the test lead from the structure and continue to test other structures by connecting that lead to the structure in question. 11.3.2.5 Measure and record structure-to-electrolyte potentials for structures that are to be evaluated. 11.3.3 Evaluation of Data Electrical continuity or discontinuity may be indicated for structures that meet the CP criterion stated in NACE SP0285. 11.4 Point-to-Point Technique 11.4.1 This technique is used to test for an indication of possible electrical continuity using a voltmeter to measure the difference in electrical potential between two underground structures. 11.4.2 To perform this test, one test lead from a voltmeter shall be connected to the structure to be tested. The second test lead from the voltmeter shall be connected to a separate structure or appurtenance that is suspected to be electrically continuous.

NACE International

21

TM0101-2012 11.4.3 With the rectifier deenergized, one technique to verify the continuity of the negative bond wire to the intended structure(s) being protected is to disconnect the negative structural lead wire from the rectifier and connect one lead of the voltmeter to this negative lead and measure the potential difference between the negative lead wire and other structures. 11.4.4 Evaluation of Data Electrical continuity or discontinuity shall be indicated for structures that meet the CP criterion stated in NACE SP0285. NOTE: Structures and appurtenances found in a UST system may misrepresent the results of this test. Galvanized pipe or conduit and coated or uncoated structures are some examples of different alloys or conditions that could cause misrepresentation of the results of this test. 11.5 Applied Current Technique 11.5.1 This technique uses either a temporary DC source or an existing interruptible CP system and basic CP test equipment to determine electrical continuity. This technique may also be used to confirm the fixed cell/moving ground and potential difference technique test results. 11.5.2 The following procedure shall be followed when testing using the applied current technique: 11.5.2.1 Make electrical contact between the reference electrode and the electrolyte at a location remote from the UST system to be tested. 11.5.2.1.1 The location should not be within the potential gradient of anodes or other structures. Placement of the reference electrode in a location that is shielded by another tank or structure may result in erroneous data concerning the continuity of the shielded tanks or structures. Alternate reference electrode placements may be necessary to determine the continuity of all structures at the test site. 11.5.2.1.2 Once placed, the reference electrode shall not be moved for the duration of this test procedure. 11.5.2.1.3 Prior to testing, existing impressed current CP systems should be turned off. If a galvanic anode CP system is being used, the anodes should be disconnected from the structure, if practical. 11.5.2.2 Measure and record the structure-to-electrolyte potential with respect to the reference electrode. 11.5.2.3 Measure and record a structure-to-electrolyte potential for other structures under test. 11.5.2.4 Use either of the following for the applied current procedure: (a) Energize the existing impressed current CP system or galvanic anode CP system; or (b) Energize a temporary groundbed. The temporary groundbed must be electrically isolated from the structures under test. NOTE: When using this technique, it is not safe to create a connection to a structure in a vapor-rich environment. Connections should not be made inside the UST above the fuel level. 11.5.2.5 Remeasure and record the structure-to-electrolyte potentials with respect to the reference electrode. 11.5.2.6 Remeasure and record the structure-to-electrolyte potentials for structures that are designed to be continuous or isolated. 11.5.3 Evaluation of Data The potentials taken before the CP system or groundbed was energized shall be compared with those taken afterward. Electrical continuity or discontinuity should be indicated for structures that meet the CP criterion stated in NACE SP0285.

22

NACE International

TM0101-2012 11.6 Invalid Techniques Techniques that use continuity testers common to the electrical trades are not valid for continuity testing on UST systems in a common electrolyte. Some equipment in this category includes the following: (a)

DC ohmmeter

(b)

Diode tester

(c)

Continuity test light

11.7 Corrective Action 11.7.1 Further investigation may be required to confirm the presence or lack of continuity, depending on the original UST system design. 11.7.2 For some UST systems, correction of the defect may preclude the installation of additional CP measures. 11.7.3 In other instances, correction of the defect may be necessary for the original UST system or supplemental CP to be totally effective.

_________________________________________________________________________ Section 12: Piping and Appurtenances 12.1 Any other cathodically protected structures associated with the UST system, such as metallic product piping and metallic 4 flexible connectors that routinely contain product, must be tested in accordance with this test method, NACE SP0169, and NACE 5 Standard TM0497. 12.2 A minimum of two potential measurements shall be taken for each piping run less than 30 m (100 ft). Three or more potential measurements shall be taken for piping runs that are 30 m (100 ft) or greater in length. When three or more potential measurements are taken, one potential measurement shall be taken near the center of the run or away from the anodes. The other two potential measurements shall be taken near the ends of the piping run.

_________________________________________________________________________ Section 13: Records 13.1 Persons performing CP testing shall provide the owner of the UST system with a record of the CP survey. 13.2 The record should contain the information identified in one of the following checklists, as appropriate (see Appendix B [Nonmandatory] for the checklists): (a) Checklist for CP Systems When the Current Cannot Be Interrupted (b) Checklist for CP Systems When the Current Can Be Interrupted

_________________________________________________________________________ References 1. NACE SP0285 (formerly RP0285) (latest revision), “Corrosion Control of Underground Storage Tank Systems by Cathodic Protection” (Houston, TX: NACE). 2. NACE/ASTM G193 (latest revision), “Standard Terminology and Acronyms Relating to Corrosion” (Houston, TX: NACE and West Conshohocken, PA: ASTM). 3. NACE SP0177 (formerly RP0177) (latest revision), “Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems” (Houston, TX: NACE). 4. NACE SP0169 (formerly RP0169) (latest revision), “Control of External Corrosion on Underground or Submerged Metallic Piping Systems” (Houston, TX: NACE).

NACE International

23

TM0101-2012 5. NACE Standard TM0497 (latest revision), “Measurement Techniques Related to Criteria for Cathodic Protection on Underground or Submerged Metallic Piping Systems” (Houston, TX: NACE). 6. NACE Publication 35201 (latest revision), “Technical Report on the Application and Interpretation of Data from External Coupons Used in the Evaluation of Cathodically Protected Metallic Structures” (Houston, TX: NACE).

_________________________________________________________________________ Bibliography Ansuini, F.L., and J.R. Dimond. “Factors Affecting the Accuracy of Reference Electrodes.” MP 33, 11 (1994): pp. 14-17. Applegate, L.M. Cathodic Protection. New York, NY: McGraw-Hill, 1960. Bushman, J.B., and F.E. Rizzo. “IR Drop in Cathodic Protection Measurements.” MP 17, 7 (1978): pp. 9-13. Corrosion Control/System Protection, Book TS-1, Gas Engineering and Operating Practices Series. Arlington, VA: American Gas Association, 1986. Dabkowski, J., and T. Hamilton. “A Review of Instant-Off Polarized Potential Measurement Errors.” CORROSION/93, paper no. 561. Houston, TX: NACE, 1993. Dearing, B.M. “The 100-mV Polarization Criterion.” MP 33, 9 (1994): pp. 23-27. DeBethune, A.J. “Fundamental Concepts of Electrode Potentials.” Corrosion 9, 10 (1953): pp. 336-344. Escalante, E., ed. Underground Corrosion, ASTM STP 741. West Conshohocken, PA: ASTM, 1981. Ewing, S.P. “Potential Measurements for Determining Cathodic Protection Requirements.” Corrosion 7, 12 (1951): pp. 410-418. Gummow, R.A. “Cathodic Protection Potential Criterion for Underground Steel Structures.” MP 32, 11 (1993): pp. 21-30. Gummow, R.A., ed. Cathodic Protection Criteria – a Literature Survey. Houston, TX: NACE, 1989. Jones, D.A. “Analysis of Cathodic Protection Criteria.” Corrosion 28, 11 (1972): pp. 421-423. Parker, M.E. Pipeline Corrosion and Cathodic Protection. 2nd ed. Houston, TX: Gulf Publishing, 1962 Peabody, A.W. Control of Pipeline Corrosion. Houston, TX: NACE, 2001. Stephens, R.W. Surface Potential Survey Procedure and Interpretation of Data – Proceedings of the Appalachian Corrosion Short Course, held May 1980. Morgantown, WV: University of West Virginia, 1980. West, L.H. Fundamental Field Practices Associated with Electrical Measurements – Proceedings of the Appalachian Corrosion Short Course, held May 1980. Morgantown, WV: University of West Virginia, 1980.

_________________________________________________________________________ Appendix A Using CP Coupons to Determine the Adequacy of Cathodic Protection (Nonmandatory) This appendix is considered nonmandatory, although it may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this standard is not required to follow, but may choose to follow, any or all of the provisions herein. A1 CP coupons, particularly when accompanied by other engineering tools and data, have been used to evaluate whether CP at 6 a test site complies with a given criterion.

24

NACE International

TM0101-2012 A2 The small size of a CP coupon may reduce the effect of voltage drops caused by currents from other sources. The magnitude of these voltage drops can be determined by interrupting CP current sources while the CP coupon is disconnected and noting whether there is a shift in the CP coupon-to-electrolyte potential. A3 These methods use CP coupons to assess the adequacy of CP applied to a selected test site. A CP coupon is a metal sample representing the UST at the test site and used for CP testing. The CP coupons used for these tests should be: (a)

Of the same material and with the same or nearly the same properties as the UST;

(b)

Known not to interfere with determining the adequacy of the CP system;

(c)

On a coated UST, the size of the CP coupon should represent the largest anticipated coating defect;

(d)

Placed at UST depth in the same backfill as the UST;

(e)

Prepared with all mill scale and foreign materials removed from the surface; and

(f)

Placed at a location of an ineffective coating, if known.

A4 During normal operations, a CP coupon has an insulated test lead brought above ground and connected to a UST test lead. The CP coupon receives CP current and represents the UST at the test site. For testing purposes, this connection is opened, and the polarized potential of the CP coupon is measured. A4.1 The time the connection is open to measure the CP coupon’s instant-off potential should be minimized to avoid significant depolarization of the CP coupon. The CP coupon is then allowed to depolarize. A4.2 If possible, CP coupon current direction and magnitude should be verified using a current clip gauge or resistor permanently placed in series with the CP coupon lead. Measurements showing discharge of current from the CP coupon should be reason to question the validity of using a CP coupon at the test site. A5 The basic test equipment for both of these tests is the same: A5.1 Voltmeter with adequate input impedance. Commonly used digital instruments have a nominal impedance of 10 megohms. An analog instrument with an internal circuit resistance of 100,000 ohms per volt may be adequate in certain circumstances if the circuit resistance is low. A potentiometer circuit may be necessary in other circumstances. A5.2 Meter leads with insulated wire and terminal connections suitable for making reliable electrical contact with the UST and reference electrode. Color-coded meter leads should be used to avoid confusion of polarity of the measured value. A5.3 A CSE or other standard reference electrode may be used. Reference electrodes that may be substituted for the CSE are described in Paragraph 5.5. A6 CP Coupon Test Method A—for Negative 850 mV Polarized Structure-to-Electrolyte Potential of a Steel UST System A6.1 This test method uses a CP coupon to assess the adequacy of CP on a steel UST system in accordance with the CP criterion stated in NACE SP0285. A6.2 Comparison with Other Methods A6.2.1

Advantages

(a) Provides a polarized CP coupon-to-electrolyte potential, free of voltage drop, with a minimum of specialized equipment, personnel, and vehicles; and (b) Provides a more comprehensive evaluation of the polarization at the test site than conventional structure-toelectrolyte potential measurements that may be influenced by the location, size, and number of coating holidays, if the UST system is coated. A6.2.2

Disadvantages

May have high initial costs to install CP coupons, especially for existing UST system.

NACE International

25

TM0101-2012 A6.3 Procedure A6.3.1

Before the test, verify that:

(a) CP equipment has been installed and is operating properly; and (b) CP coupon is in place and connected to a structure test lead. NOTE: Sufficient time should be allowed for the structure and CP coupon potentials to reach polarized values. A6.3.2

Determine the location of CP coupon placement. Selection of a site may be based on:

(a) Location accessible for future monitoring; (b) Other protection systems, structures, and anodes that may influence the structure-to-electrolyte and CP coupon-toelectrolyte potentials; (c) Electrical midpoints between protection devices; (d) Known location of an ineffective coating when the UST system structure is coated; and (e) Location of a known or suspected corrosive environment. A6.3.3 Make electrical contact between the reference electrode and the electrolyte at the test site as close to the CP coupon as is practicable. A6.3.4 Record the location of the reference electrode to allow it to be returned to the same location for subsequent tests. A6.3.5 Connect the voltmeter to the CP coupon test lead and reference electrode as described in Paragraph 5.6. A6.3.6 Measure and record the structure and CP coupon “on” potentials. A6.3.7 Momentarily disconnect the CP coupon test lead from the structure test lead and immediately measure and record the CP coupon-to-electrolyte instant-off potential and its polarity with respect to the reference electrode. This should be performed quickly to avoid depolarization of the CP coupon. A6.3.8 Reconnect the CP coupon test lead to the structure test lead for normal operations. A6.4 Evaluation of Data A6.4.1 CP may be judged adequate at the test site if the polarized (instant-off) structure-to-electrolyte potential meets the CP criterion stated in NACE SP0285. A6.4.2 The polarized potential of the CP coupon depends on the CP coupon surface condition, the soil in which the CP coupon is placed, its level of polarization, and the amount of time it has been polarized. Therefore, the polarized potential of the CP coupon may not be the same as that of the structure and may not accurately reflect the polarization on the structure at the CP coupon location. A6.4.3 The polarization measured on the structure is a resultant of the variations of polarization on the structure at the test site. The causes of these variations include the structure surface condition, soil strata variations, oxygen differentials, and length of time the structure has been polarized. Making precise comparisons between the polarization of the structure and the polarization of the CP coupon may not be possible. A6.5 Monitoring When the polarized CP coupon-to-electrolyte potential has been determined to be equal to or exceed a negative 850 mV, the UST system “on” potential may be used for monitoring unless significant environmental, structural, coating integrity, or CP system parameters have changed. A7 CP Coupon Test Method B—for 100 mV Cathodic Polarization of a Steel UST System

26

NACE International

TM0101-2012 A.7.1 This test method uses CP coupon polarization decay or polarization formation to assess the adequacy of CP on a steel UST system in accordance with the CP criterion stated in NACE SP0285. A7.2 Comparison with Other Methods A7.2.1 Advantages (a) Measures CP coupon-to-electrolyte polarization decay or polarization formation with a minimum of specialized equipment, personnel, and vehicles; and (b) Provides an indication of the amount of polarization present at the test site without interrupting the CP current supplied to the UST system. A7.2.2 Disadvantages Initial installation of CP coupons can be expensive, especially for an existing UST system. A7.3 Procedure A7.3.1 Before the test, verify that: (a) CP equipment is installed and operating properly; and (b) CP coupon is in place and connected to a UST system test lead. NOTE: Sufficient time shall be allowed for the UST system and CP coupon potentials to reach polarized values. A7.3.2 Determine the location of CP coupon placement for potential measurements. Selection of a site may be based on: (a) Location accessible for future monitoring; (b) Other protection systems, structures, and anodes that may influence the structure-to-electrolyte and CP coupon-toelectrolyte potentials; (c) Electrical midpoints between protection devices; (d) Known location of an ineffective coating if the structure is coated; and (e) Location of a known or suspected corrosive environment. A7.3.3 Make electrical contact between the reference electrode and the electrolyte at the test site as close to the CP coupon as is practicable. A7.3.4 Record the location of the reference electrode to allow it to be returned to the same location for subsequent tests. A7.3.5 Connect the voltmeter to the CP coupon test lead and reference electrode as described in Paragraph 5.6. A7.3.6 Measure and record the structure and CP coupon on potentials. A7.3.7 Disconnect the CP coupon test lead from the structure test lead and immediately measure the CP coupon-toelectrolyte potential. The CP coupon-to-electrolyte potential becomes the baseline value from which polarization decay is measured. A7.3.8 Record the CP coupon-to-electrolyte instant-off potential and its polarity with respect to the reference electrode. A7.3.9 Leave the CP coupon test lead disconnected to allow the CP coupon to depolarize. A7.3.10 Measure and record the CP coupon-to-electrolyte potential periodically. The difference between it and the instant-off potential is the amount of polarization decay. Continue to measure and record the CP coupon-to-electrolyte potential until it either:

NACE International

27

TM0101-2012 (a) Has become at least 100 mV less negative than the instant-off potential; or (b) Has reached a stable depolarized level. A7.3.11 Reconnect the CP coupon test lead to the tank test lead for normal operations. A7.3.12 The use of polarization formation, as stated in the CP criterion, may also be used to assess the adequacy of CP. The procedure is different in that a baseline value for the CP coupon is measured prior to connection to the UST system. That potential is then compared to the instant-off potential of the CP coupon after it has been allowed to polarize. A7.4 Evaluation of Data A7.4.1 CP may be judged adequate at the test site if the polarization decay or polarization formation meets the criterion 1 stated in NACE SP0285. A7.4.2 The depolarized potential of the CP coupon depends on the CP coupon surface condition, the soil in which the CP coupon is placed, its level of polarization, and its time polarized. Therefore, the depolarized potential of the CP coupon may not be the same as that of the structure and may not accurately reflect the polarization on the structure at the CP coupon location. A7.4.3 The polarization measured on the structure is a result of the variations of polarization on the UST system at the test site. These variations are caused by the structure surface condition, soil strata variations, oxygen differentials, and time the structure has been polarized. Making precise comparisons between the polarization of the structure and the polarization of the CP coupon may not be possible. A7.5 Testing When at least 100 mV or more of polarization decay or polarization formation has been measured, the structure “on” potential at the test site may be used for monitoring unless significant environmental, structural, coating integrity, or CP system parameters have changed.

28

NACE International

TM0101-2012 _________________________________________________________________________ Appendix B Checklists for CP Systems (Nonmandatory) This appendix is considered nonmandatory, although it may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this standard is not required to follow, but may choose to follow, any or all of the provisions herein.

Checklist for CP Systems When the Current Cannot Be Interrupted 

Identify UST system owner, UST facility, CP tester, tester’s qualifications, and reason for CP survey.



Describe UST system and CP system.



Construct site drawing depicting all pertinent components of the UST and CP systems at the facility.



Review any previous CP design/repair/testing data that may be available.



Perform continuity testing of all pertinent metallic components at the UST facility by the fixed cell/ moving ground, point-topoint, or applied current technique.



Obtain and record local and/or remote structure-to-electrolyte potentials on every cathodically protected structure according to this test method. Indicate location (by code or other means) of reference electrode placement on site drawing for each structure-to-electrolyte potential that was obtained during the CP survey.



Describe any repairs or modifications that were made to the CP system.



Indicate whether or not each protected structure met the –850 mV on criterion for both the local and remote reference electrode placement by indicating pass/fail/inconclusive.



Indicate CP criteria used in the CP survey.



Indicate any action required as a result of the CP survey (for example: none, retest, or repair and retest).



Provide UST system owner with any other type(s) of documentation that may be necessary to adequately describe the CP survey, including the operating status and any repairs or recommendations.

NACE International

29

TM0101-2012

Checklist for CP Systems When the Current Can Be Interrupted 

Identify UST system owner, UST facility, CP tester, tester’s qualifications, and reason for CP survey.



Describe UST system and CP system.



Construct site drawing depicting all pertinent components of the UST and CP systems at the facility.



Review any previous CP design/repair/testing data that may be available.



Check rectifier for proper operation and measure output voltage/amperage with portable multimeter and indicate all other pertinent information.



Measure and record current output of all positive and negative circuits.



Conduct continuity testing of all pertinent metallic components at the UST facility by the fixed cell/ moving ground, point-topoint, applied current technique.



Obtain and record structure-to-electrolyte potentials on every cathodically protected structure with the reference electrode placed in the soil directly over the structure under test with the protective current applied (on).



Obtain and record structure-to-electrolyte potentials on every cathodically protected structure without moving reference electrode from placement used to obtain on potential with the protective current temporarily interrupted (instant-off).



Perform 100 mV polarization test if all protected structures did not meet the –850 mV instant-off criterion, and record the results.



Indicate location (by code or other means) of reference electrode placement on site drawing for each structure-toelectrolyte potential that was obtained.



Describe any repairs or modifications that were made to the CP system



Indicate whether or not each protected structure met the -850 mV instant-off criterion or the 100 mV cathodic polarization criterion by indicating pass/fail



Indicate criteria used in the CP survey.



Indicate any action required as a result of the CP survey (for example: none, retest, or repair and retest).



Provide UST system owner with any other type(s) of documentation that may be necessary to adequately describe the CP survey, including the operating status and any repairs or recommendations.

30

NACE International

TM0101-2012

NACE International

ISBN 1-57590-137-4 31