Mississippi Administrative Code › Title 11 - Mississippi Department of Environmental Quality › Part 5 - Underground Storage Tank Regulations › Chapter 2 - Mississippi Commission on Environmental Quality Underground Storage Tanks Regulations Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks (UST) (Adopted March 22, 1989; Amended August 25, 2011, Last Amended August 23, 2018) › Appendix 11-5-2-280.1 - GUIDELINES FOR THE EVALUATION OF UNDERGROUND STORAGE TANK CATHODIC PROTECTION SYSTEMS › Appendix 11-5-2-280.1-B - GLOSSARY

Current through June 25, 2024
100 mV POLARIZATION
- One of the three
					 criteria that are commonly accepted as indicating adequate cathodic protection
					 has been achieved. It is typically measured by interrupting the protective
					 current on an impressed current system. When the current is interrupted, an
					 "instant off" potential is recorded and the structure under cathodic protection
					 is then allowed to depolarize until a change of at least 100 mV in potential is
					 observed. Not more than 24 hours should be allowed for the depolarization to
					 occur when conducting this test.
850 ON
- One of the three criteria that are
					 commonly accepted as indicating adequate cathodic protection has been achieved.
					 It is measured with the protective current applied and is typically the only
					 measurement possible with galvanic systems since the anodes cannot be
					 disconnected. This criterion is not applicable to impressed current systems
					 since a large portion of the "on" measurement can be comprised of a voltage
					 drop when the protective current is applied.
850 OFF
- One of the three criteria that are
					 commonly accepted as indicating adequate cathodic protection has been achieved.
					 It is measured with the protective current interrupted (either the power is cut
					 off to the rectifier or the sacrificial anodes are disconnected). This
					 criterion is considered by most to be the best indicator that adequate cathodic
					 protection has been provided.
ANODE
- The electrode of an electrochemical
					 cell where oxidation (corrosion) occurs. With respect to cathodic protection,
					 it can be thought of as the place where electrons leave the surface of a metal.
					 Common galvanic anodes are zinc and magnesium.
AMPERE
(AMP) - The basic unit of current flow
					 in an electric circuit. Amperage can be thought of as "gallons per minute" in a
					 water system.
AS BUILT DRAWINGS
- Drawings that show how a
					 system was actually installed in the field. Sometimes, unforeseen factors
					 prevent the installation of a system as it was intended in the design drawings
					 and this is why it is important to have detailed and accurate "as built"
					 drawings.
ATTENUATION
- The protective effects of
					 cathodic protection current diminish as you move away from the source of the
					 protective current. To illustrate this, on an impressed current system where
					 the ground bed is installed only on one side of the tank bed, the end of the
					 tanks away from the ground bed will receive less protective current than the
					 side of the tanks closest to the anodes. Attenuation of protective current
					 applies to galvanic systems as well.
CATHODE
- The electrode of an electrochemical
					 cell where reduction (and no corrosion) occurs. With respect to cathodic
					 protection, it can be thought of as the place where current enters the surface
					 of a metal.
CATHODIC PROTECTION
- The technique of causing
					 the entire surface of a metallic structure to become a cathode with respect to
					 its external environment (soil). This is accomplished by supplying an electric
					 current sufficient to overcome the tendency of naturally occurring electrical
					 currents to leave the metallic structure.
CATHODIC PROTECTION EVALUATION
- The
					 interpretation of whether or not a cathodic protection system is providing
					 sufficient corrosion protection. An evaluation incorporates all cathodic
					 protection testing, surveys, rectifier operation/output measurements,
					 consideration of voltage drops, condition of dielectric coatings, continuity,
					 bond integrity, circuit integrity and any other factors or site specific
					 conditions that may have an influence on the operation and effectiveness of a
					 cathodic protection system.
CATHODIC PROTECTION SURVEY
- Refers to the
					 process whereby all of the structure-to-soil measurements necessary to
					 contribute to the final evaluation of a system are obtained.
CATHODIC PROTECTION TEST-
Refers to the
					 process whereby only a single structure-to-soil measurement is obtained.
CONTINUITY
- As related to cathodic
					 protection, continuity means that two metallic structures are electrically
					 continuous. With impressed current systems all protected structures must be
					 continuous and this is normally accomplished through the use of wires referred
					 to as continuity bonds.
CORROSION
- The deterioration of a material
					 (usually a metal) caused by an electro-chemical reaction with its environment.
					 Corrosion of metals involves the flow of electrons (current) between an anode
					 and a cathode. Corrosion will occur where the electrons leave the surface of a
					 metal.
CURRENT TEST
-A method of temporarily creating
					 an impressed current cathodic protection system on a galvanically protected
					 structure so that it can be determined how much protective current is necessary
					 in order to achieve adequate cathodic protection. This is normally done by
					 connecting a 12-volt battery to the structure to be tested and to a temporary
					 anode.
DIELECTRIC MATERIAL
- A coating that does not
					 conduct electricity. Various coatings are utilized and some examples are the
					 "fusion-bonded epoxy" found on factory coated steel piping and coal tar epoxies
					 commonly found on sti-P3 tanks.
DISTRIBUTED GROUND BED
- Used to describe an
					 anode configuration in which the anodes are more or less equally distributed
					 around the metallic structure that is intended to be protected.
ELECTROLYTE
- As related to UST cathodic
					 protection systems, electrolyte refers to the soil and/or water surrounding the
					 metallic structure that is under cathodic protection.
ELECTROMAGNETIC INTERFERENCE
- As related to
					 corrosion protection, it is an external electrical current that causes an error
					 in a voltmeter measurement. Sources are commonly associated with high voltage
					 AC power lines, radio frequency transmitters and airport radar systems.
FAIL
-See Section 7.1.4.
FIELD INSTALLED
- Refers to any impressed
					 current system or sacrificial anode cathodic protection system that is
					 installed at a pre-existing UST location or when sacrificial anodes are
					 installed on new metallic pipe in the field. Any cathodic protection system
					 except for those associated with unmodified sti-Pj tanks may be thought of as
					 "field installed".
FINAL POTENTIAL (VOLTAGE)
- The voltage that
					 is observed at the end of the depolarization period associated with the
					 measurement of "100 mV polarization". The final voltage must be at least 100 mV
					 less than the "instant off' voltage in order to meet the 100 mV polarization
					 criterion for adequate cathodic protection.
"FIXED CELL - MOVING GROUND"
- A technique for
					 measuring continuity in a UST system whereby the reference electrode is placed
					 in the soil at a location remote from the UST system and is left undisturbed
					 (fixed cell) while potentials are measured on various parts of the UST system
					 (moving ground).
GALVANIC (SACRIFICIAL) ANODE
- A metal of high
					 electro-potential (see Appendix J) that is used to protect another metal. Zinc
					 and magnesium are two metals that are commonly utilized in the protection of
					 UST systems.
GALVANIC CATHODIC PROTECTION
- A cathodic
					 protection system that utilizes sacrificial anodes to provide the protective
					 current. The anode will corrode (sacrifice itself) instead of the metal it is
					 intended to protect. The anode provides a protective current (reverses the
					 electron flow) because it has a higher electrochemical potential than the metal
					 it is intended to protect. Galvanic systems are normally limited to the
					 protection of well coated structures because they have a very low driving
					 potential.
IMPRESSED CURRENT ANODE
- A metal that is
					 utilized to deliver the current from a rectifier to the soil in order to
					 protect the intended metallic structure. Impressed current anodes are commonly
					 made of graphite, high silicon cast iron and "mixed-metal oxides" because the
					 metal must be highly resistant to corrosion in order to have an acceptably long
					 life span.
IMPRESSED CURRENT CATHODIC PROTECTION
- A
					 cathodic protection system in which the protective current is supplied by an
					 external source (rectifier). The level of protective current that is delivered
					 to the structure is adjustable and is much higher than that associated with
					 galvanic anodes. For this reason, impressed current systems are utilized on
					 those UST systems that are uncoated or require a high amount of protective
					 current.
INCONCLUSIVE
- See Section 7.1.4.
INSTANT OFF POTENTIAL (VOLTAGE)
- The voltage
					 that is observed momentarily after the power to an impressed current cathodic
					 protection system is interrupted. It is used as the base line from which to
					 begin calculating a "100 mV polarization". The second number that appears after
					 the current is interrupted is considered the proper value to represent the
					 instant off potential.
ISOLATION
- As related to cathodic protection,
					 isolation means that two metallic structures are electrically discontinuous.
					 With galvanic systems a protected structure must be electrically isolated and
					 this is normally accomplished through the use of nylon bushings and dielectric
					 unions.
LOCAL POTENTIAL (VOLTAGE)
- The
					 structure-to-soil potential of a metallic structure that is measured with the
					 reference electrode placed in the soil immediately over the protected
					 structure.
NACE INTERNATIONAL
- Acronym for National
					 Association of Corrosion Engineers International.
NATIVE POTENTIAL
(VOLTAGE) - The
					 structure-to-soil potential exhibited before any cathodic protection is
					 applied.
ON POTENTIAL (VOLTAGE)
- The structure-to-soil
					 potential that is measured with the protective current applied.
PARALLEL CIRCUIT
- Can be caused by the person
					 conducting the test making contact with a metallic part of the test leads, or
					 reference electrode when conducting structure-to-soil potential measurements.
					 The creation of parallel paths must be avoided since inadvertent errors can be
					 introduced.
PASS
-See Section 7.1.4
PASSIVATION
- When a metal undergoes
					 passivation, an oxidation layer forms on the surface of the metal due to
					 corrosion and can be defined as the loss of chemical reactivity. The oxidation
					 layer acts as a coating and prevents or slows further corrosion of the metallic
					 object since oxygen is prevented from reaching the underlying metal.
PHOTOVOLTAIC EFFECT
- Sunlight striking the
					 electrolyte solution in a copper-copper sulfate reference electrode can cause
					 an error in the observed structure-to-soil potential and must be
					 avoided.
"POINT-TO-POINT"
- A technique for measuring
					 continuity in a UST system whereby each lead of a voltmeter is connected to the
					 two metallic structures of interest (negative lead to one structure and
					 positive to the other). The voltage difference (if any) measured with the
					 voltmeter connected in this manner indicates if continuity is present or
					 not.
POLARIZATION
- The change in the
					 structure-to-soil potential of a metallic structure due to the application of a
					 protective current. In this guidance document, polarization is considered to
					 mean cathodic polarization - that is, the potential of the metal is shifted in
					 the negative direction.
POLARIZED POTENTIAL
- The structure-to-soil
					 potential of a metallic structure that is observed after the protective current
					 is applied and sufficient time has elapsed for the structure to completely
					 polarize.
RAISED EARTH
- Term used to describe the high
					 voltage gradient found in the soil around an active impressed current or
					 sacrificial anode. Placement of the reference electrode in proximity to an
					 active anode will cause an abnormally high (more negative) structure-to-soil
					 potential than would be present if the anode were not in close
					 proximity.
RECTIFIER
- A device utilized in impressed
					 current systems that changes AC power to DC power.
REFERENCE ELECTRODE
- Also referred to as a
					 reference cell or a half-cell. A device whose electrochemical potential is
					 constant that is used to measure the structure-to-soil potential of buried
					 metallic structures. The potential that is observed on the buried metallic
					 structure is relative to the potential of the reference electrode. The
					 potential of a buried metallic structure would be zero if it were of the exact
					 same composition as the reference electrode if all sources of measurement error
					 were eliminated.
RESISTANCE
- A measurement of the tendency of
					 a substance to inhibit the flow of electrical current. Resistance in UST
					 cathodic protection systems is generally meant to refer to the electrical
					 properties of the backfill materials (soil).
REMOTE EARTH
- The structure-to-soil potential
					 of a metallic structure that is measured with the reference electrode placed in
					 the soil at a point well away (remote) from the protected structure. Remote
					 earth is generally thought of as at least 25 feet and not more than 100 feet
					 away. Remote earth is established when the observed structure-to-soil potential
					 does not significantly change no matter how far away the reference electrode is
					 from the protected structure.
SACRIFICIAL ANODE
- See Galvanic Anode.
SHIELDING
- A structure that prevents or
					 diverts an electrical current from reaching the desired location. Normally
					 thought of as something that stops a reference electrode from being able to
					 "see" the metallic structure that you trying to measure.
sti-P3 TANK
- A steel tank manufactured to the
					 standard created by the Steel Tank Institute that comes from the factory with a
					 "pre-engineered" cathodic protection system. The "P3" means that the steel tank
					 is protected in three ways: 1) A protective dielectric coating is factory
					 applied; 2) Sacrificial anodes (normally zinc) are factory installed on the
					 tanks and 3) dielectric bushings are installed to facilitate electrical
					 isolation of the tank.
STRAY CURRENT
- An electrical current that
					 travels along an unintended path. Normally thought of as a current from some
					 external source that enters a protected metallic structure at one point that
					 then exits at another point. The point where the stray current exits the
					 protected structure can be subject to intense corrosion and failure may rapidly
					 occur.
STRUCTURE-TO-SOIL POTENTIAL
- Also known as
					 "pipe-to-soil potential' or "structure-to-electrolyte potential" - The
					 difference in the potential of the surface of a buried metallic structure and
					 the electrolyte (soil) that surrounds it with respect to a reference electrode
					 in contact with the electrolyte (soil). Can be thought of as the voltage
					 difference between a buried metallic structure and the soil that it is buried
					 in.
VOLTAGE
- The basic unit of force in an
					 electric circuit. Voltage is equivalent to pounds per square inch in a water
					 system.
VOLTAGE (IR) DROP
- With respect to UST
					 cathodic protection systems, voltage drops may be thought of as any voltage
					 that causes an error in the observed structure-to-soil potential. Whenever a
					 current is flowing through a resistance, a voltage drop is present and is part
					 of the voltage measurement obtained.