2. • Virtually no practical and engineering material is
stable. The rate of decay varies depending upon the
material and its environment.
• The human system cannot endure
– Temp above 50 C or below 20 C
– Pressures above or below our atmospheres
– Presence of harmful gases such as CO, H2S, and
H2.
• Thus, analogous to human system, engineering
materials also require protection like
– coatings, inhibitors, alloy addition, design
procedures, maintenance, inspection and re-
furnishing.
3. Corrosion is the disintegration of an engineered material
into its constituent atom due to chemical reactions with
its surroundings. In the most common use of the word,
this means electrochemical oxidation of metals in
reaction with an oxidant such as O2.
4. EFFECTS OF CORROSION
• Reduces Strength
• Life time is reduced
• Metallic properties are lost
• Wastage of metal
5. IMPORTANCE OF CORROSION
DATA
5 mpy Good corrosion
resistant material
5 to 50 mpy Low corrosion
resistant material
50 mpy Unsuitable as
constructional
material
12. STRESS CORROSION
BRITTLE CRACKS FORM AT
THE SITES OF STRESS.
FAILURE CAN BE FAST.
FAILURE CAN OCCUR AT
STRESS LOADS FAR BELOW
YIELD STRENGTH.
THREE CONDITIONS REQUIRED FOR MOST
COMMON KIND ARE -----
METAL UNDER DISSOLVED CHLORIDE
TENSILE OXYGEN ION
STRESS
16. ACIVE CORROSION
PROTECTION
• The aim of active corrosion protection is to
influence the reactions which proceed during
corrosion, it being possible to control not only the
package contents and the corrosive agent but also
the reaction itself in such a manner that corrosion
is avoided.
.• Examples of such an approach are the
development of corrosion-resistant
alloys.
17. PERMANENT CORROSION
PROTECTION
• The purpose of permanent corrosion protection
methods is mainly to provide protection at the
place of use. The stresses presented by climatic,
biotic & chemical factors are relatively slight in
this situation.
• For example, in factories shed are
protected from extreme variations in
temperature, which is frequently the
cause of condensation.
