This part deals with introduction to corrosion and corrosion failures. It is very costly phenomenon and should be fought leadi8ng to corrosion prevention and neutralization of corrosion. The US is loosing Billions of Dollars due to corrosion either due to deterioration and imobilization of structures or due to corrosion means of protection as well as the remedial costs of the effected components.

1. PART III
INTRODUCTION TO CORROSION
FAILURES AND REASONS

2. INTRODUCTION TO CORROSION
Definition
Corrosion is defined as the deterioration and the
degradation of a metallic component within an industrial
project leading to great reductions in weight, dimensions
and weakening of the strength as well as complete
immobilization of any industrial component or even
explosions and hence destruction of the project.

3. Materials Used in Offshore & Coastal Water:
- Must withstand very harsh marine environment.
• Structures: under the severe impact of wind, waves currents, ice.
(hurricane, typhoon, storms, earthquake (tsunami), ……etc)
• Ocean water is highly corrosive (electrolyte)
• Bio-fouling
•Should be non-toxic to marine organism (paint).
•High pressure in deep water
- Materials used in Marine and Offshore Fields of Practice:
•Metals:
-Steels & special steels (Stainless steels including Duplex Steels),
-Aluminum,
-Titanium,
-Non-ferrous Alloys (Copper-nickel)
• Nonmetallic Materials
-Thermoplastics
-Composites*
-Cement & Concrete* (cheap and usually anti-corrosion)
-Wood

4. What is meant by “ MARINE CORROSION”?
Marine corrosion means the breaking
down of essential properties in a marine
material due to electro-chemical
reactions with its surroundings.
In the most common use of the word, this
means a loss of electrons of metals
reacting with water and oxygen.
Weakening of iron due to oxidation of the
iron atoms is a well-known example of
electrochemical corrosion. This is
commonly known as rusting or general
corrosion.
Corrosion is Defined as the Loss of electrons from the surface
due to hydroxyl formation

5. Localized types of corrosion that is
confined to small area.
Localized corrosion often occurs due to a
concentrated cell. A concentrated cell is an
electrolytic cell in which the electromotive
force is caused by a concentration of some
components in the electrolyte. This
difference leads to the formation of:
2-1- Pitting Corrosion
2-2- Crevice Corrosion
2-3- Filiform Corrosion

6. Corrosion at sea
Sea water is a highly corrosive electrolyte towards mild steel. This ship has suffered
severe damage in the areas which are most buffeted by waves, where the protective
coating of paint has been largely removed by mechanical action.

7. Examples of
Rust, the most familiar
corrosion in Pipelines

8. Galvanic Corrosion - Example of the higher
corrosion activity usually existing at a brass to iron
connection within a pipeline.

9. Marine Corrosion: is the deterioration of
metals in the marine environment due to
electro-chemical reaction. (see pp161 (old
E. 129-130) regarding electrochemical
reactions)
•Ships, marinas, pipelines, offshore
structures, desalination plants, ocean
energy conversion device & heat
exchangers are some examples of systems
that experience marine corrosion.
•Exposure of components to sea water can
be continuous or intermittent.
•Maintenance costs for ships, offshore
structures and related equipment are
dependent on how marine corrosion issues
and failures are managed.

10. •Crevice Corrosion &
Pitting.
occurs in narrow metal to
metal or non-metal to metal
gaps where the convection
of water is hampered.
Aggressive ions like chlorides
must be present in the
electrolyte. Crevice corrosion
develops quite similar to
pitting corrosion after the
initiation stage. Examples of
such geometries include
flanges, gaskets, disbonded
linings/coatings, fasteners,
lap joints and surface
deposits.

11. •Erosion Corrosion arises from a
combination of chemical attack and the
physical abrasion as a consequence of the fluid
motion. The best way to limit erosion-corrosion
is to design systems that will maintain a low
fluid velocity and to minimize sudden line
size changes and elbows. The photo shows
erosion-corrosion of a copper-nickel tube in a
seawater surface. An imperfection
on the tube surface
probably cause an
eddy current which
provided a perfect
location for
erosion-corrosion

12. •Stress Corrosion results from the combination
of an applied tensile stress & a corrosive
environment.
Some materials only become susceptible to
corrosion in a given environment once a tensile
stress is applied. Once the stress cracks begin, they
easily propagate throughout the material, which in
turn allows additional corrosion and cracking to
take place. The tensile stress is usually the result
of expansions and contractions
that are caused by violent temperature
changes or thermal cycles. Atoms of metal at
stressed areas have high energy , i.e. very active
High localized corrosion rates at such areas
Localized metal loss leading to Cracking.
Environmental Effects-Stress Corrosion Cracking SCC

13. Crevice )‫إنشقاق‬( corrosion

14. Bacterial Corrosion Problem
A classic example of
Microbiological
Corrosion Attack in a
#2 Fuel Storage Tank.
This form of attack is
more common on
above ground storage
tanks where the
ambient summer
temperatures are
ideal for bacterial
colony growth.
Bacteria Corrosion Ballast Water
Tanks

15. Offshore Rigs and Platforms as well
as deep water Structures can suffer
from worsened Random Stochastic
environment Corrosion and thus
Collapse
Offshore structures, especially risers
and pipelines are suffering from
random stochastic wave aggression of
extreme surrounding environment

16. EXFLOITATION CORROSION
What does Exfoliation
Corrosion mean?
Exfoliation corrosion is a form of
intergranular corrosion which
involves selective attack of a
metal at or adjacent to grain
boundaries. In this process,
corrosion products formed force
metal to move away from the
body of the material, giving rise
to a layered appearance.
Exfoliation corrosion is also
known as layer corrosion or
lamellar corrosion.
Note that blistering of coatings
can lead to exfoliation corrosion.

17. Preventing Corrosions
•Design
•Coating
•Cathodic Protection
-Impressed cathodic
protection (requires to use of
external electric power.
- Galvanic cathodic
protection

18. PMS – Petroleum Marine Services Resistance versus External Corrosion
Alexandria, 16-18 May 2006
1- Cathodic protection
• Cathodic protection implies that the corrosion
protection is achieved by making the pipeline to
be protected by being the cathode in an
electrochemical cell.
• The cathodic protection requires an electrically
conductive medium (electrolyte) and a current
source which may be:
1- a corroding metal : sacrificial anode
cathodic protection
2- a direct current source : impressed current
cathodic protection
• Subsea pipelines are generally protected with a
combination of :
– corrosion coating (organic)
– sacrifical anodes
• Reference document : DNV RP B401 Cathodic
Protection design
A potential of - 0.80 V relative to
Ag/AgCl/seawater reference
electrodes is accepted as the
protective potential for carbon
steel and low-alloy steel in
seawater.
The aim of the cathodic
protection is to polarise the
structure below this potential.
Electrochemical potential :
Anode materials many anode
materials are proprietary alloys-
Al-based alloy, Zn-based alloy,
Mg-based.

19. PMS – Petroleum Marine Services Resistance versus External Corrosion
Alexandria, 16-18 May 2006
Cathodic protection with sacrifical anodes
• Typical anodes geometry :
– Stand-off
– Flush mounted
– Bracelet
• Bracelet anodes mostly used for pipelines
• The design of the sacrificial anode system should specify the anode type, the anode size, the anode
material, the anode spacing, and the attachment of anodes on the structure to be protected.
• Characteristics of the anodes :
– electrochemical efficiency
– utilisation factor
Detrimental effects of cathodic protection may occur for potentials below -1.10 V (rel.
Ag/AgCl/seawater)
– Risk of disbonding of coatings
– Hydrogen induced stress cracking (risk of brittle failure
• Note : Anodes are exposed and may be damaged during installation

20. 2-IMPRESSED CURRENT PROTECTION SYSTEM

21. END