Biological corrosion is the deterioration of metal caused by living organisms like bacteria, algae, and barnacles. These organisms can influence corrosion through their chemical processes and deposits. Both aerobic and anaerobic bacteria can impact corrosion by changing conditions like increasing acidity. Sulfate-reducing bacteria are particularly problematic as they produce sulfides that accelerate corrosion. Fungi and macroorganisms like barnacles also influence corrosion through organic acid production and deposits. Proper identification of microbes and prevention techniques like coatings, cathodic protection, and environment modification can help mitigate biological corrosion.

1. By
Paidi Hemanth Kumar
(18MM4110)
Under the guidance of
Prof. K S GHOSH

2. 
 Biological Corrosion is not a type of corrosion, it is
the deterioration of a metal by corrosion processes
that occur directly or indirectly as a result of the
activity of living organisms.
 These organisms include micro forms such as
bacteria and macro types such as algae and
barnacles. Microscopic and macroscopic organisms
have been observed to live and reproduce in
mediums with pH values between 0 and 11, a
temperatures between 30 and 180⁰F
INTRODUCTION

3. 
Living Organisms are sustained by chemical reactions.
That is, organisms ingest a reactant or food and
eliminate waste products. These processes can affect
corrosion behaviour in the following ways.
 By directly influencing anodic and cathodic
reactions.
 By influencing protective surface films.
 By creating corrosive conditions.
 By producing deposits.
How this affect Corrosion
behaviour

4. 
 Usually , microorganisms are classified according to
their ability to grow in the presence or absence of
oxygen.
 Organisms that require oxygen in their metabolic
processes are termed aerobic; they grow only in
nutrient mediums containing dissolved oxygen.
 Other organisms, called Anaerobic, grow most
favourably in environments containing little or no
oxygen.
Biological Corrosion by
Microorganisms

5. 
 Probably the most important anaerobic bacteria that
influence the corrosion behaviour of buried steel
structures are the sulphate reducing types which are
desulfuricans. These reduce sulphate to sulphide
according to the following schematic equation:
SO4
2- + 4 H2 S2- + 4 H2O
 Sulphate reducing bacteria is more prevalent under
anaerobic conditions, as in wet clay, boggy soils, and
marshes
Mechanism of Anaerobic
bacteria

6. 
 The presence of sulphide ion markedly influences
both the cathodic and anodic reactions occurring on
iron surfaces.
 Sulphide tends to retard the cathodic reactions,
particularly hydrogen evolution, and accelerates
anodic dissolution.
 Under most conditions, the acceleration of
dissolution is the most pronounced effect, which
causes increased corrosion.
Contd.

7. 
 Aerobic sulphur oxidizing bacteria such as
thiobaccillus thiooxidans, are capable of oxidizing
elemental sulphur or sulphur bearing compounds to
sulphuric acid according to the following equation:
2 S + 3 O2 + 2 H2O 2 H2SO4
 These sulphur oxidizing bacteria are capable of
creating extremely corrosive conditions.
Mechanism of Aerobic
bacteria

8. 
 These organisms require sulphur in either elemental
or combined form for their existence and are
therefore found frequently in sulphur fields, in oil
fields, and in and about sewage disposal piping that
contains sulphur bearing organic waste products.
 In the case of sewage pipe lines, sulphuric oxidizing
bacteria cause rapid acid attack of cement piping.
Contd.

9. 
 Sulphate reducing and sulphur oxidizing bacteria
can operate in cyclic fashion when soil conditions
change.
 That is sulphate reducing bacteria grow rapidly
during rainy seasons where the soil is wet and air is
excluded.
 Sulphate oxidizing bacteria grow rapidly during dry
seasons where air permeates the soil. In certain areas
this cyclic effect causes extensive corrosion damage
of buried steel pipelines.
Contd.

10. 
External corrosion on buried
gas transmission pipeline

11. 
 Several types of bacteria utilize hydrocarbons and
can damage asphaltic pipe coatings.
 Iron bacteria are a group of microorganisms that
assimilates ferrous iron from solution and precipitate
it as ferrous or ferric hydroxide in sheets
surrounding their cell walls.
 The growth of iron bacteria frequently results in
tubercles on steel surfaces and tends to produce
crevice attack.
Other Microorganisms

12. 
 Certain bacteria are capable of oxidizing ammonia to
nitric acid. Dilute nitric acid corrodes iron and most
other metals.
 Finally most bacteria also produce carbon dioxide,
which can contribute to the formation of carbonic
acid and increases corrosivity.
Contd.

13. 
 It is important to correctly diagnose the presence of
microbiological corrosion before applying corrective
measures.
 The most direct and accurate method of
identification is accomplished by culturing samples
of soil and examining them for evidence of
microorganisms.
 In case of sulphur reducing bacteria, the existence of
sulphide corrosion product on buried steel structures
is usually a strong indication of biological activity.
Prevention of
Microbiological corrosion

14. 
 There are several other general techniques for
preventing microbiological corrosion.
 Coating the buried structure with asphalt, enamel,
plastic tape, or concrete is frequently used to prevent
contact between the steel structure and the
environment.
 Cathodic protection has also been used to prevent
microbiological corrosion and is especially effective
when used with coatings. In some cases it is possible
to alter the environment and thereby reduces the
effect of microbiological corrosion.
Contd.

15. 
 Corrosion inhibitors can be added and germicides
such as chlorine and chlorinated compounds can be
employed in recirculating systems.
 In some cases it is possible to avoid wet, boggy soils
in constructing pipeline networks.
 The use of substitute materials such as asbestos and
plastic pipe in place of steel pipe has also been used
as an effective means of preventing the detrimental
effects of microbiological activity in certain
undesirable soil locations.
Contd.

16. 
 Fungus and mold are the same as in much as both
terms refers to a group of plants characterized by
their lack of chlorophyll.
 These species assimilate organic matter and produce
considerable quantities of organic acids including
oxalic, lactic, acetic and citric acids.
 Fungi are capable of growing on a variety of
substrates and are a particularly troublesome
problem especially in tropical areas.
Macroorganisms

17. 
 The most familiar type of attack of this kind is the
mildwing of leather and other fabrics. In addition,
fungi can attack rubber and bare and coated metal
surfaces.
 In many instances the presence of fungi does not
cause severe mechanical damage but affects the
appearance of the product, which is not desirable.
 In addition to producing organic fluids, fungi can
also intitiate crevice attack of metal surfaces.
Contd.

18. 
 Aqueous organisms, Both fresh water and salt water
can sustain thousands of types of animal and plant
life, including barnacles, mussels, algae and others.
 These animal and plant forms attach themselves to
solid surfaces during their growth cycle. The
accumulation of these organisms causes crevice
corrosion and probably more important, fouling of
structures.
 Ship bottoms rapidly accumulate barnacles and
other organisms that markedly affect the
streamlining and increase power requirements.
Contd.

19. 
 Similarly, the accumulation of macroorganisms in
heat exchangers and other such devices severely
limits heat transfer and fluid flow and may result in
complete obstruction.
 The accumulation of aqueous macroorganisms is a
function of environmental conditions.
 The most severe problem occurs in relatively shallow
water, since in deeper water there are no surfaces to
which the organisms may adhere. Thus, harbour
conditions are specially conducive to the formation
of deposits on ship hulls.
Contd.

20. 
 The fouling of stainless steel and iron occurs initially at
about the same rate in seawater.
 However, after some exposure, the surface of the iron is
covered by a loosely adhering iron oxide and fouling
tends to be less on iron than on stainless steel after long
exposure periods.
 Fouling by organisms is most effectively inhibited by the
use of anti fouling paints. These paints contain toxic
substances, usually copper compounds. They function by
slowly releasing copper ions into the aqueous
environment, which poisons the growth of barnacles and
other creatures.
Contd.

21. 
 Mold growth on coated and uncoated metal surfaces can
be prevented or reduced by periodic cleaning.
 Also, reducing the relative humidity during storage and
the employment of toxic organic agents have also been
found effective in reducing mold growth on metal
surfaces.
 Mold growth on rubber is particularly troublesome in
underground cables, since localized perforation of the
rubber coating results in electrical leakage.
 The substitution of synthetic instead of natural rubber has
been found to be an effective method for preventing this
kind of failure.
Prevention of
Macrobiological Corrosion

22. 