金属腐蚀的种类英文

1.1 pitting corrosion

Pitting corrosion and pitting corrosion. Pitting corrosion is large and small, in general, the depth of

the pit is larger than the diameter of the pit. Pitting often occurs on the surface of a passive film or

a protective film on the metal.

Due

to

the

non-uniformity

defects,

impurities

and

other

solutes

in

metal

materials,

when

the

medium contains some active anion (such as Cl -), the activity of anion was first adsorbed on the

metal surface at some point, so that the metal surface passivation film damage. Once this layer

Metal corrosion

Metal corrosion

When the passivation film is destroyed and lack of self passivation ability, corrosion occurs on the

surface of the metal. This is because the metal leakage easily in the metal surface defects, which

were activated, and the passivation film still is a blunt state, so that the formation of active blunt

corrosion

battery,

because

the

anode

area

is

much

smaller

than

the

cathode

area,

anode

current

density, the corrosion to the depths of the development, the metal surface soon it was a corrosion

hole, this phenomenon is called pitting.

In the petroleum and chemical corrosion failure types, the pitting corrosion is about 20% ~ 25%.

The conditions for the formation of active anion accumulation and concentration are easily formed

in the medium containing active anions, which cause the formation of pitting corrosion. The rough

surface is more prone to pitting corrosion than the smooth surface.

PH value and temperature rise will increase the tendency of pitting corrosion. The oxidation of

metal ions (such as Fe3+, Cu2+, Hg2+, etc.) can promote the generation of pitting corrosion. But

some oxygen anion (such as hydroxide, chromate, nitrate and sulfate) can prevent the pitting.

Although little weight loss due to pitting corrosion, the anode area is very small, so the corrosion

rate is very fast, it can cause serious equipment perforation, so that a large number of oil, water

and

gas

leakage,

sometimes

even

cause

serious

accidents

such

as

fire

and

explosion,

very

dangerous.

Pitting

corrosion,

stress

corrosion

and

corrosion

fatigue

and

so

on,

in

many

cases,

pitting corrosion is the origin of these types of corrosion.

1.2 crevice corrosion (Corrossion Crevice)

In

the

electrolyte,

the

narrow

gap

formed

between

metal

and

metal

or

metal

and

non

metal

surfaces, mobile related substances inside the crevice was blocked, the formation of concentration

cell, resulting in local corrosion, the corrosion is called crevice corrosion. Flange connection in the

device often occurs in crevice corrosion, washer, lining, winding and metal overlap, it can appear

in different metals and different corrosion medium, thus causing a serious obstacle to the normal

operation of production equipment, and even accidents. Crevice corrosion is the most attention to

the corrosion of titanium and titanium alloys. In the medium, the oxygen concentration increases,

the

crevice

corrosion

quantity

increases;

the

pH

value

decreases,

the

anodic

dissolution

rate

increases,

the

crevice

corrosion

quantity

also

increases;

the

concentration

of

the

active

anion

increases, the crevice corrosion sensitivity is increased. However, the increase in the number of

oxygen anions will reduce the amount of crevice corrosion.

金属腐蚀

1.3 stress corrosion

The material in corrosive medium and in particular the static tensile stress (including external load,

thermal stress, cold working and heat processing, welding residual stress caused by the cracks, and

wedge

rust

stress),

lower

than

the

ultimate

strength

of

brittle

cracking

phenomenon,

known

as

stress corrosion cracking.