Nace CP 1, Course Manual

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NACE GLOSSARY OF CORROSION-RELATED TERMS
©
2002, NACE International. This publication may not be reprinted without the written consent of NACE International.
Page 12 of 18
MODULUS OF
ELASTICITY
A measure of the stiffness or
rigidity of a material. It is actually
the ratio of stress to strain in the
elastic region of a material. If
determined by a tension or
compression test, it is also called
Young’s Modulus or the
coefficient of elasticity.
N
NATURAL DRAINAGE
Drainage from an underground or
submerged metallic structure to a
more negative (more anodic)
structure, such as the negative
bus of a trolley substation.
NEAR-WHITE BLAST
CLEANED SURFACE
A near-white blast cleaned
surface, when viewed without
magnification, shall be free of all
visible oil, grease, dust, dirt, mill
scale, rust, coating, oxides,
corrosion products, and other
foreign matter. Random staining
shall be limited to not more than
5% of each unit area of surface
(approximately 58 cm
2
[9.0 in.
2
]),
and may consist of light
shadows, slight streaks, or minor
discolorations caused by stains
of rust, stains of mill scale, or
stains of previously applied
coating. [See NACE No.
2/SSPC-SP 10.]
NEGATIVE RETURN
A point of connection between
the cathodic protection negative
cable and the protected
structure.
NERNST EQUATION
An equation that expresses the
exact electromotive force of an
electrochemical cell in terms of
the activities of products and
reactants of the cell.
NERNST LAYER
The diffusion layer at the surface
of an electrode in which the
concentration of a chemical
species is assumed to vary
linearly from the value in the bulk
solution to the value at the
electrode surface.
NOBLE
The positive direction of
electrode potential, thus
resembling noble metals such as
gold and platinum.
NOBLE METAL
(1) A metal that occurs
commonly in nature in the free
state. (2) A metal or alloy whose
corrosion products are formed
with a small negative or a
positive free-energy change.
NOBLE POTENTIAL
A potential more cathodic
(positive) than the standard
hydrogen potential.
NORMALIZING
Heating a ferrous alloy to a
suitable temperature above the
transformation range
(austenitizing), holding at
temperature for a suitable time,
and then cooling in still air to a
temperature substantially below
the transformation range.
O
OPEN-CIRCUIT
POTENTIAL
The potential of an electrode
measured with respect to a
reference electrode or another
electrode in the absence of
current.
ORGANIC ZINC-RICH
COATING
Coating containing a metallic zinc
pigment (typically 75 wt% zinc or
more in the dry film) in an organic
resin.
OVERVOLTAGE
The change in potential of an
electrode from its equilibrium or
steady-state value when current
is applied.
OXIDATION
(1) Loss of electrons by a
constituent of a chemical
reaction. (2) Corrosion of a
metal that is exposed to an
oxidizing gas at elevated
temperatures.
OXIDATION-REDUCTION
POTENTIAL
The potential of a reversible
oxidation-reduction electrode
measured with respect to a
reference electrode, corrected to
the hydrogen electrode, in a
given electrolyte.
OXYGEN
CONCENTRATION CELL
[See Differential Aeration Cell. ]
P
PAINT
A pigmented liquid or resin
applied to a substrate as a thin
layer that is converted to an
opaque solid film after
application. It is commonly used