Nace CP 1, Course Manual

Page: 259 / 535

NACE GLOSSARY OF CORROSION-RELATED TERMS
©
2002, NACE International. This publication may not be reprinted without the written consent of NACE International.
Page 13 of 18
as a decorative or protective
coating.
PAINT SYSTEM
[See Coating System .]
PARTING
[See Dealloying. ]
PASSIVATION
A reduction of the anodic
reaction rate of an electrode
involved in corrosion.
PASSIVATION
POTENTIAL
[See Primary Passive Potential. ]
PASSIVE
(1) The positive direction of
electrode potential. (2) A state
of a metal in which a surface
reaction product causes a
marked decrease in the corrosion
rate relative to that in the
absence of the product.
PASSIVE-ACTIVE CELL
An electrochemical cell, the
electromotive force of which is
caused by the potential
difference between a metal in an
active state and the same metal
in a passive state.
PASSIVITY
The state of being passive.
PATINA
A thin layer of corrosion product,
usually green, that forms on the
surface of metals such as copper
and copper-based alloys
exposed to the atmosphere.
pH
The negative logarithm of the
hydrogen ion activity written as:
pH
= -log
10
(a
H
+
)
where a
H
+
= hydrogen ion activity
= the molar concentration of
hydrogen ions multiplied by the
mean ion-activity coefficient.
PICKLING
(1) Treating a metal in a chemical
bath to remove scale and oxides
(e.g., rust) from the surface. (2)
Complete removal of rust and
mill scale by acid pickling, duplex
pickling, or electrolytic pickling.
[See SSPC-SP 8.]
PICKLING SOLUTION
A chemical bath, usually an acid
solution, used for pickling.
PIGMENT
A solid substance, generally in
fine powder form, that is
insoluble in the vehicle of a
formulated coating material. It is
used to impart color or other
specific physical or chemical
properties to the coating.
PIPE-TO-ELECTROLYTE
POTENTIAL
[See Structure-to-Electrolyte
Potential. ]
PIPE-TO-SOIL
POTENTIAL
[See Structure-to-Electrolyte
Potential. ]
PITTING
Localized corrosion of a metal
surface that is confined to a small
area and takes the form of
cavities called pits.
PITTING FACTOR
The ratio of the depth of the
deepest pit resulting from
corrosion divided by the average
penetration as calculated from
mass loss.
PLASTIC DEFORMATION
Permanent deformation caused
by stressing beyond the elastic
limit.
PLASTICITY
The ability of a material to deform
permanently (nonelastically)
without fracturing.
POLARIZATION
The change from the open-circuit
potential as a result of current
across the electrode/electrolyte
interface.
POLARIZATION
ADMITTANCE
The reciprocal of polarization
resistance.
POLARIZATION CELL
A DC decoupling device
consisting of two or more pairs of
inert metallic plates immersed in
an aqueous electrolyte. The
electrical characteristics of the
polarization cell are high
resistance to DC potentials and
low impedance of AC.
POLARIZATION CURVE
A plot of current density versus
electrode potential for a specific
electrode/electrolyte
combination.
POLARIZATION DECAY
The decrease in electrode
potential with time resulting from
the interruption of applied
current.
POLARIZATION
RESISTANCE
The slope (dE/di) at the corrosion
potential of a potential (E)-current
density (i) curve. (The measured
slope is usually in good
agreement with the true value of