Corrosion, fouling, and boring of ship hulls cause significant economic problems. Fouling begins as microorganisms like bacteria and algae form biofilms on surfaces exposed to the marine environment. There are over 4000 fouling organisms including bacteria, algae, fungi, and protozoa. Corrosion is the conversion of metal to a non-metallic state through chemical or electrochemical reactions with the environment. Common types of corrosion include uniform corrosion, galvanic corrosion, crevice corrosion, pitting corrosion, microbiologically induced corrosion, stress corrosion, erosion corrosion, and selective corrosion. Various prevention methods can be used depending on the corrosion type.

1. SUBMTTED BY-
Koushik Das
1 st sem,Roll no. 10
School Of Industrial Fisheries
C.U.S.A.T

2.  Corrosion, fouling & boring of the hulls of fishing vessels
are serious problems of “high economic significance”.
 Fouling in marine environment is initiated by the micro-
organisms like bacteria, fungi & algae to the surface of
the exposed material known as “Bioflim”.
 More than 4000 species of animals and plants which are
include bacteria, diatoms, algae, fungi, protozoan, etc. are
recorded from fouling communities (Venkatesan et
al.,2006)

3.  Corrosion is the term used to described the conversion
of a metal to a non-metallic state.
 Corrosion is defined as the destruction of a metal
by chemical or electro-chemical reaction with it’s
environment.
Metal + Environment Metal Compound + Free Energy
(Fe; Zn) (H2 o; O2; H2S) (Metallic Oxide, Hydroxide,
Sulphide)
(Fe2 O3, Fe(OH)2, Fe(OH)3,
ZnS)

4. TYPES OF CORROSION:-
UNIFORM/ GENERAL CORROSION
GALVANIC/ TWO METAL CORROSION
CONCENTRATION CELL/ CREVICE
CORROSION
PITTING CORROSION
MICRO-BIOLOGICALLY INDUCED
CORROSION
STRESS CORROSION
EROSION CORROSION
FILLIFORM CORROSION
SELECTIVE CORROSION

5.  In this type of corrosion take place uniformly over the
surface of the metals.
 Uniform corrosion can be prevented by selecting
corrosion resistant alloys, apply chemical inhibitors &
coating cathodic protection.
 Metals such as steel that do not form passive films
show uniform corrosion.

7.  Corrosion which occurs when dissimilar metals are in
electric contact in presence of an electrolyte such as
seawater is termed as galvanic corrosion.
 Galvanic corrosion can be prevented by selecting the
alloys of similar electro-chemical nature (making the
area more actively corroding material ‘anode’ larger
than the ‘cathode’).

9.  It is a localized corrosion which may occur in small
areas of stagnant solution in crevice, joints & under
corrosion deposits.
 This can be prevented by closing the crevices with
non-absorbent materials & preventing build up of
scales or any solids on the surface of material.

11.  It is a highly localized corrosion occurs on the metal
surface. It occurs as a process of local anodic
dissolution where metal loss is the presence of small
anode & large cathode.
 Pitting corrosion can be prevented by increasing the
velocity of media or removal deposits of solids form
exposed metal surface.
 Suitable selection of alloys, chemical inhibitor & de-
aeration of aerated environment will help to reduce
pitting.

13.  In the micro-biologically induced corrosion, micro-
organisms like bacteria or fungi are involved in the
degradation of material.
 The type of organism involved in the process depend
on the substrate and the environment.
 It is a severe problem in the case of cooling water &
submerged pipelines in soil.

15.  Stress corrosion cracking may be occurs at stresses well
below the yield point of the alloy.
 Generally, corrosion does not lead to the mechanical
failure of structures or component because the
reduction in cross sectional area is controlled either by
choosing a corrosion resistant alloy or by applying
suitable protective coating.

17.  Interaction with particulate matter present in the
fluid, flow of liquids in tubes especially at bends can
leads to mechanical damage of the internal surface of
tubes leading to erosion corrosion.

19.  This is a process in which one of the materials of a
binary alloy selectively dissolves leaving a spongy mass
behind. An example is the corrosion in brass and
bronze materials.