ISO 12473:2017 海水中の陰極防食の一般原則 | ページ 5

3.1

acidity

presence of an excess of hydrogen ions over hydroxyl ions (pH < 7)

3.2

alkalinity

presence of an excess of hydroxyl ions over hydrogen ions (pH > 7)

3.3

anaerobic condition

absence of free oxygen dissolved in the electrolyte

3.4

calcareous deposits

minerals precipitated on the metallic cathode because of the increased alkalinity caused by cathodic protection

3.5

cathodic disbondment

failure of adhesion between a coating and a metallic surface that is directly attributable to the application of cathodic protection

3.6

cathodic protection system

entire installation that provides cathodic protection

Note 1 to entry: It may include anodes, power source, cables, test facilities, isolation joints, electrical bonds.

3.7

coating breakdown factor

fc

ratio of cathodic current density for a coated metallic material to the cathodic current density of the bare material

3.8

copper/copper sulphate reference electrode

reference electrode consisting of copper in a saturated solution of copper sulphate

3.9

dielectric shield

alkali resistant organic coating applied to the structure being protected in the immediate vicinity of an impressed current anode to enhance the spread of cathodic protection and minimize the risk of hydrogen damage to the protected structure in the vicinity of the anode

3.10

driving voltage

difference between the structure/electrolyte potential and the anode/electrolyte potential when the cathodic protection is operating

3.11

electro-osmosis

passage of a liquid through a porous medium under the influence of a potential difference

3.12

environmentally assisted cracking

cracking of a susceptible metal or alloy due to the conjoint action of an environment and stress

3.13

groundbed

system of immersed electrodes connected to the positive terminal of an independent source of direct current and used to direct the cathodic protection current onto the structure being protected

3.14

hydrogen embrittlement

process resulting in a decrease of the toughness or ductility of a metal due to absorption of hydrogen

3.15

hydrogen stress cracking

HSC

cracking that results from the presence of hydrogen in a metal and tensile stress (residual and/or applied)

Note 1 to entry: HSC describes cracking in metals which may be embrittled by hydrogen produced by cathodic polarization without any detrimental effect caused by specific chemicals such as sulphides.

3.16

isolating joint (or coupling)

electrically discontinuous joint or coupling between two lengths of pipe, inserted in order to provide electrical discontinuity between them

3.17

master reference electrode

reference electrode, calibrated with the primary calibration reference electrode, used for verification of reference electrodes used for field or laboratory measurements

3.18

over-polarization

occurrence in which the structure to electrolyte potentials are more negative than those required for satisfactory cathodic protection

Note 1 to entry: Over-polarization provides no useful function and might even cause damage to the structure.

3.19

pitting resistance equivalent

PREN

indication of the resistance of a corrosion resistant alloy to pitting in the presence of water, chlorides and oxygen or oxidation environment, accounting for the beneficial effects of nitrogen

Note 1 to entry: For the purposes of this document, PREN is calculated as follows: PREN = % Cr + 3,3[(% Mo) + 0,5 (% W)] + 16 (% N).

3.20

potential gradient

difference in potential between two separate points in the same electric field

3.21

primary calibration reference electrode

reference electrode used for calibration of master reference electrodes is the normal hydrogen electrode (N.H.E.)

Note 1 to entry: The official reference electrode, standard hydrogen electrode (S.H.E.), which considers the fugacity coefficient for hydrogen gas and the activity coefficient for H⁺ ions, is practically impossible to manufacture.

3.22

protection current

current made to flow into a metallic structure from its electrolytic environment in order to achieve cathodic protection of the structure

3.23

reference electrode

electrode having a stable and reproducible potential that is used as a reference in the measurement of electrode potentials

Note 1 to entry: Some reference electrodes use the electrolyte in which the measurement is carried out. Their potential varies according to the composition of this electrolyte.

3.24

resistivity (of an electrolyte)

resistivity is the resistance of an electrolyte of unit cross section and unit length

Note 1 to entry: It is expressed in ohm.metres (Ω.m). The resistivity depends, amongst other things, upon the amount of dissolved salts in the electrolyte.

3.25

saturated calomel reference electrode

reference electrode consisting of mercury and mercurous chloride in a saturated solution of potassium chloride

3.26

silver/silver chloride reference electrode

reference electrode consisting of silver, coated with silver chloride, in an electrolyte containing a known concentration of chloride ions

Note 1 to entry: Silver/silver chloride/ saturated KCl electrodes are electrodes currently used in the laboratory and for master reference electrode.

Note 2 to entry: Silver/silver chloride/seawater (Ag/AgCl/seawater) electrodes are electrodes currently used for field measurements in seawater.

3.27

slow strain rate test

test for evaluating susceptibility of a metal to environmentally assisted cracking (3.12 in this document) that most commonly involves pulling a tensile specimen to failure in a representative environment at a constant displacement rate chosen to generate nominal strain rates usually in the range 10⁻⁵ s⁻¹ to 10⁻⁸ s⁻¹

Note 1 to entry: Slow strain rate testing may also be applied to other specimen geometries, e.g. bend specimens.

3.28

specified minimum yield strength

SMYS

minimum yield strength prescribed by the specification under which steel components are manufactured, obtained through standard analysis and representing a probabilistic value

Note 1 to entry: It is an indication of the minimum stress steel components may experience that will cause plastic (permanent) deformation (typically 0,2 %).

3.29

stray currents

current flowing through paths other than the intended circuits

3.30

structure to electrolyte potential

difference in potential between a structure and a specified reference electrode in contact with the electrolyte at a point sufficiently close to, but without actually touching the structure, to avoid error due to the voltage drop associated with any current flowing in the electrolyte

3.31

sulphate reducing bacteria

SRB

group of bacteria that are found in most soils and natural waters, but active only in conditions of near neutrality and absence of oxygen and that reduce sulphates in their environment, with the production of sulphides and accelerate the corrosion of structural materials

3.32

telluric currents

electrical currents induced by time varying changes in the earth's magnetic field

Note 1 to entry: They are able to flow in metallic conductors laid in the soil or in the sea.

3.33

zinc reference electrode

electrode consisting of pure zinc or zinc alloy specific for anodes in contact with the electrolyte in which the measurements are carried out

Note 1 to entry: Zinc reference electrodes are currently used for measurements in seawater carried out at permanent locations.