TB 43-0213
2-2.
The Four Elements of Rusting.
a. Rusting of iron, steel, or any metal alloy is caused
by the electrochemical reaction described in para-
graph 2-1. This reaction is divided into four parts or
elements:
(1) A positive reaction.
(2) A negative reaction.
(3) A path for negative particles to flow.
(4) A path for positive particles to flow.
b. In the explanation of the rusting process, the
positive and negative polarization of the iron atoms
constitute the first two elements. A path for positive and
negative particles to flow is described in the "oxidation
half" of the "Oxidation-Reduction Reaction. " If any of
NOTE
these elements are interrupted, the circuit is broken
and no rusting will occur.
One key to the Corrosion Prevention and
Control Program is an update of all vehicle
c. The best means of breaking the rusting circuit is
Preventive
semiannual
Maintenance
to bond a nonmetallic substance to the metal as a
Checks and Services (PMCS) to emphasize
barrier between the metal and the environment. To
early detection and repair of rust damaged
some degree, paint accomplishes such a barrier. On
areas before the condition is allowed to
well maintained exterior surfaces, paint will go a long
advance beyond Stage 2 rust.
way toward forestalling rust. But nothing can stop
rusting altogether. Eventually, moisture will work its
(2) Stage 2 Rust (see Figure 2-3), Powdered,
way to the metal even beneath rustproofing material.
granular, or scaled condition exists on the surface
metal. Rusty red, black, or white corrosion deposits are
d. With a greater awareness of rust, the rusting
present, Metal surface may be etched or pitted. Metal
process, the stages of rust, and rustproofing procedures,
beneath the corroded area is still sound.
the damage of this form of corrosion can be minimized
within the Army to the point of zero impact upon the
service life of any Army vehicle.
2-3.
The Four Stages of Rust.
a. Rust has been categorized into four distinct
stages. These stages of deterioration have been stan-
dardized within the Army in order to communicate the
condition of the metal. The four stages apply to painted
metal surfaces:
(1) Stage 1 Rust (see Figure 2-2). The painted
surface is bubbly or the paint bubbles have broken to
reveal rusty red, black, or white corrosion deposits on
the metal surface. This may be accompanied by minor
etching or pitting of the metal. In Stage 1 rust, no scale
is present but the metal may have loose, powdery, or
granular deposits on the surface. Base metal is sound.
2-3
