Turkey Ship Repair & Maintenance Services

To run the Fortran/77 program HOLTROP, the Personal Computer must contain a CONFIG.SYS file with the following statements:
BUFFERS=nn
FILES=nn
DEVICE=C:\WINDOWS\COMMAND\ANSI.SYS
in which nn is generally 40 or more.
For running the program under Windows, this CONFIG.SYS file must be visible in the Explorer.
If not so, set in the Explorer: | View | Folder Options | Tab View | Hidden Files | Show all Files |.
After these modifications: Restart your computer !!!

Input Data

TEXT Text line with general information

SLPP              Length between perpendiculars (m)
SLWL             Length on the water line (m)
BR                  Breadth (m)
DRAFT          Amidships draft (m)
TRIM              Trim (m)
VOL               Moulded volume of displacement (m3)
SLCB             C.O.B. forward of SLWL / 2 (%)
CWP               Water plane area coefficient (-)
CM                 Amidships section coefficient (-)
SHULL          Wetted area hull (m2)
If unknown: SHULL = 0.0
SSKIN                       Additional skin friction coefficient
SSERV           Multiplication factor for service condition
CAFT             Shape coefficient aft (-)
U-form with Hogner stern:   CAFT = +10.0
Normal form:                         CAFT = 0.0
V-form:                                 CAFT = -10.0
Pram with gondola:               CAFT = -25.0
SRUD             Wetted area rudder (m2)
CRUD                        Rudder coefficient (-)
Rudder behind skeg:             CRUD = 1.5 - 2.0
Rudder behind stern:            CRUD = 1.3 - 1.5
Twin-screw balance rudders:            CRUD = 2.8
SAPP              Wetted area appendages (m2)
SAPP = SUM [sapp(i)]
CAPP             Equivalent appendage factor (-)
CAPP = SUM [capp(i) * sapp(i)] / SUM [sapp(i)]
Shaft brackets:                      capp(i) = 3.0
Skeg:                         capp(i) = 1.5 - 2.0
Strut bossings:                       capp(i) = 3.0
                                               Hull bossings:             capp(i) = 2.0
Shafts:                                   capp(i) = 2.0 - 4.0
Stabilizer fins:                       capp(i) = 2.8
Dome:                                   capp(i) = 2.7
Bilge keels:                capp(i) = 1.4
ABULB          Cross sectional area bulbous bow (m2)
No bow correction: ABULB = 0.0
HBULB          Centroid of bulbous bow cross section to keel (m)
If ABULB = 0.0 then: HBULB can have any value
DBTT             Diameter of bow thruster tunnel (m)
If no bow thruster:    DBTT = 0.0
If N bow thrusters:    DBTT = DBTT * SQRT(N)
CBTT              Resistance coefficient of bow thruster tunnel
If no bow thruster:                            CBTT = 0.000
Thruster in cylindrical part of bow: CBTT = 0.003
Thruster at the worst location:          CBTT = 0.012
AT                  Area of immersed transom (m2)
SLR                Length of the run (m)
If unknown:   SLR = 0.0
ALFA             Half angle of entrance of the water line (deg)
If unknown:   ALFA = 0.0
NPTOP           Number of propellers (-)
NPROP = 0: No calculation of W, T and RRE
NPROP = 1: Calculation of W, T and RRE
NPROP = 2: Calculation of W, T and RRE

Note: Start input of remaining data on a new line

If NPROP = 1 or NPROP = 2:
DP                  Diameter of propeller (m)
AAE               Expanded blade area ratio (-)
PPD                Pitch-diameter ratio (-)
NV                 Number of ship speeds, max. 25 (-)
VK(1:NV)      Array with NV ship speeds (kn)

Example of an Input Data File

M.V. Hollandia   DRAFT = 9.00 meter
193.10 196.70 30.80 9.00 0.00 31282 -0.03 0.708 0.965
0.0 0.000350 1.30 0.0    60.0 1.4     0.0 0.0     0.00   4.84   2.60 0.010
0.0 0.0 0.0     1
6.15 0.9000 0.9626
25    1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25

Example of an Output Data File

------------------------------------------------------------------------

PROGRAM: HOLTROP VERSION: 03 APRIL 2000 JOURNEE

               CALCULATION OF STILL WATER RESISTANCE OF A SHIP
               ***********************************************
                                HOLTROP 1984
                                ************

DATE: 04-04-2000 TIME: 09:41

------------------------------------------------------------------------

INPUT DATA:
***********

M.V. Hollandia DRAFT = 9.00 meter

LENGTH BETWEEN PERPENDICULARS .... SLPP : 193.10 meter
LENGTH ON THE WATERLINE .......... SLWL : 196.70 meter
BREADTH ............................ BR : 30.80 meter
MIDSHIP DRAFT ................... DRAFT : 9.00 meter
TRIM ............................. TRIM : 0.00 meter

MOULDED VOLUME OF DISPLACEMENT .... VOL : 31282 cub. meter
C.O.B. FORWARD OF SLWL/2 ......... SLCB : -0.03 % SLWL

WATERPLANE AREA COEFFICIENT ....... CWP : 0.708
MIDSHIP SECTION COEFFICIENT ........ CM : 0.965

WETTED AREA HULL ............... ISHULL :      0 sq. meter
ADDITIONAL SKIN FRICTION COEFF .. SSKIN : 0.000 /1000
SERVICE MULTIPLICATION FACTOR ... SSERV :   1.30
SHAPE COEFFICIENT AFT ............ CAFT :    0.0
WETTED AREA RUDDERS .............. SRUD :   60.0 sq. meter
RUDDER COEFFICIENT ............... CRUD :    1.4
WETTED AREA APPENDAGES ........... SAPP :    0.0 sq. meter
EQUIVALENT APPENDAGE FACTOR ...... CAPP :    0.0
CROSS SECTION AREA BULBOUS BOW .. ABULB :    0.0 sq. meter
CENTOID OF BULBOUS BOW TO KEEL .. HBULB :   4.84 meter
DIAMETER OF BOW THRUSTER TUNNEL .. DBTT :   2.60 meter
RESISTANCE COEFF. OF BOW THRUSTER CBTT : 0.010
AREA OF IMMERSED TRANSOM ........... AT :    0.0 sq. meter
LENGTH OF THE RUN ................. SLR :   0.00 meter
HALF ANGLE OF ENTRANCE ........... ALFA :    0.0 degree

NUMBER OF PROPELLERS ............ NPROP : 1

DIAMETER OF PROPELLER .............. DP : 6.15 meter
EXPANDED BLADE AREA RATIO ......... AAE : 0.900
PITCH-DIAMETER RATIO .............. PPD : 0.963

NUMBER OF SHIP SPEEDS ........ NV :     25
SHIP SPEEDS (knots) .... VK(1:NV) :    1.0   2.0   3.0   4.0   5.0
                                       6.0   7.0   8.0   9.0 10.0
                                      11.0 12.0 13.0 14.0 15.0
                                      16.0 17.0 18.0 19.0 20.0
                                      21.0 22.0 23.0 24.0 25.0

STILL WATER PERFORMANCE ACCORDING TO HOLTROP, 1984
**************************************************

SHIP    FRICT   RESIDU    TOTAL    FRICT   RESIDU    TOTAL        WAKE   THRUST    REL.R
SPEED    RESIS    RESIS    RESIS    COEFF    COEFF    COEFF       FRACT    FRACT    EFFIC
                                     *1000    *1000    *1000
(kn)     (kN)     (kN)     (kN)      (-)      (-)      (-)         (-)      (-)      (-)

1.00      0.1      3.2      3.3    2.138    1.682    3.820       0.266    0.193    0.983
2.00      0.3     11.9     12.2    1.937    1.576    3.513       0.260    0.193    0.983
3.00      0.7     25.6     26.3    1.831    1.521    3.353       0.257    0.193    0.983
4.00      1.2     44.0     45.2    1.762    1.485    3.247       0.255    0.193    0.983
5.00      1.9     67.1     68.9    1.711    1.458    3.169       0.253    0.193    0.983
6.00      2.7     94.7     97.4    1.671    1.438    3.108       0.252    0.193    0.983
7.00      3.7    126.7    130.4    1.638    1.420    3.058       0.251    0.193    0.983
8.00      4.8    163.2    168.0    1.610    1.406    3.016       0.250    0.193    0.983
9.00      6.1    203.9    210.1    1.586    1.394    2.980       0.249    0.193    0.983
10.00      7.8    249.0    256.8    1.565    1.386    2.951       0.249    0.193    0.983
11.00     10.0    298.3    308.3    1.547    1.382    2.929      0.248    0.193    0.983
12.00     13.4    351.9    365.2    1.530    1.385    2.915      0.248    0.193    0.983
13.00     18.7    409.6    428.3    1.515    1.397    2.912      0.247    0.193    0.983
14.00     27.3    471.4    498.7    1.501    1.423    2.924    0.247    0.193    0.983
15.00     40.8    537.4    578.3    1.488    1.465    2.953      0.246    0.193    0.983
16.00     61.4    607.5    668.9    1.477    1.526    3.003      0.246    0.193    0.983
17.00     91.4    681.7    773.1    1.466    1.608    3.074      0.246    0.193    0.983
18.00    133.7    759.9    893.6    1.456    1.714    3.169    0.246    0.193    0.983
19.00    190.1    842.1   1032.2    1.446    1.840    3.286       0.245    0.193    0.983
20.00    263.1    928.4   1191.5    1.437   1.986    3.423       0.245    0.193    0.983
21.00    361.4   1018.6   1380.0    1.429    2.167    3.596       0.245    0.193    0.983
22.00    494.4   1112.9   1607.2    1.421    2.395    3.816       0.244    0.193    0.983
23.00    659.0   1211.1   1870.1    1.414    2.649    4.063       0.244    0.193    0.983
24.00    835.5   1313.2   2148.7    1.406    2.880    4.287       0.244    0.193    0.983
25.00   1003.7   1419.3   2423.0    1.400    3.055    4.455       0.244    0.193    0.983

                   COEFFICIENTS BASED ON:
                      LENGTH, LPP : 193.10 m
                      WETTED AREA :   6417 m2

------------------------------------------------------------------------------

CORROSION

MetaVEnvironment Reactions

1. Principles of Corrosion and Oxidation

Basic Concepts of Corrosion
Appendix - Classification of Corrosion Processes
Nature of Films, Scales and Corrosion Products on Metals
Effects of Metallurgical Structure on Corrosion
Corrosion in Aqueous Solutions
Passivity and Localised Corrosion
Localised Corrosion
Bimetallic Corrosion
Lattice Defects in Metal Oxides
Continuous Oxide Films
Discontinuous Oxide Films
Erosion Corrosion

2. Environments
Effect of Concentration, Velocity and Temperature

The Atmosphere
Natural Waters
Sea Waters
Soil in the Corrosion Process
The Microbiology of Corrosion
Chemicals
Corrosion by Foodstuffs
Mechanisms of Liquid-metal Corrosion
Corrosion in Fused Salts
Corrosion Prevention in Lubricant Systems
Corrosion in the Oral Cavity
Surgical Implants

3. Ferrous Metals and Alloys

Iron and Steel
Low-alloy Steels
Stainless Steels
Corrosion Resistance of Maraging Steels
Nickel-Iron Alloys
Cast Iron
High-nickel Cast Irons
High-chromium Cast Irons
Silicon-Iron Alloys
Amorphous (Ferrous and Non-Ferrous) Alloys

4. Non-Ferrous Metals and Alloys
Aluminium and Aluminium Alloys
Copper and Copper Alloys
Lead and Lead Alloys
Magnesium and Magnesium Alloys
Nickel and Nickel Alloys
Tin and Tin Alloys
Zinc and Zinc Alloys

5. Rarer Metals
Beryllium
Molybdenum
Niobium
Titanium and Zirconium
Tantalum
Uranium
Tungsten

6. The Noble Metals
The Noble Metals

7. High-Temperature Corrosion
Environments
The Oxidation Resistance of Low-alloy Steels
High-temperature Corrosion of Cast IronHigh-alloy Steels
Nickel and its Alloys

8. Effect of Mechanical Factors on Corrosion
Thermodynamics and Kinetics of Gas-Metal Systems
Mechanisms of Stress-corrosion Cracking
Stress-corrosion Cracking of Ferritic Steels
Stress-corrosion Cracking of Stainless Steels
Stress-corrosion Cracking of High-tensile Steels
Stress-corrosion Cracking of Titanium, Magnesium and
Aluminium Alloys
Corrosion Fatigue
Fretting Corrosion
Cavitation Damage
Outline of Fracture Mechanics
Stress-corrosion Test Methods
Appendix - Stresses in Bent Specimens

9. Design and Economic Aspects of Corrosion
Economic Aspects of Corrosion
Corrosion Control in Chemical and Petrochemical Plant
Design for Prevention of Corrosion in Buildings and Structures
Design in Marine and Offshore Engineering
Design in Relation to Welding and Joining
Appendix - Terms Commonly Used in Joining

10. Cathodic and Anodic Protection
Principles of Cathodic Protection
Sacrificial Anodes
Impressed-current Anodes
Practical Applications of Cathodic Protection
Stray-current Corrosion
Cathodic-protection Interaction
Cathodic-protection Instruments
Anodic Protection

11. Pretreatment and Design for Metal Finishing
Pickling in Acid
Chemical and Electrolytic Polishing
Pretreatment Prior to Applying Coatings
Design for Corrosion Protection by Electroplated Coatings
Design for Corrosion Protection by Paint Coatings

12. Methods of Applying Metallic Coatings
Electroplating
Principles of Applying Coatings by Hot Dipping
Principles of Applying Coatings by Diffusion
Principles of Applying Coatings by Metal Spraying
Miscellaneous Methods of Applying Metallic Coatings

13. Protection by Metallic Coatings
The Protective Action of Metallic Coatings
Aluminium Coatings
Cadmium Coatings
Zinc Coatings
Tin and Tin Alloy Coatings
Copper and Copper Alloy Coatings
Nickel Coatings
Chromium Coatings
Noble Metal Coatings

14. Protection by Paint Coatings
Paint Application MethodsPaint Formulation
The Mechanism of the Protective Action of Paints
Paint Failure
Paint Finishes for Industrial Applications
Paint Finishes for Structural Steel for Atmospheric Exposure
Paint Finishes for Marine Application
Protective Coatings for Underground Use
Synthetic Resins
Glossary of Paint Terms

15. Chemical Conversion Coatings
Phosphate Coatings
Chromate Treatments
Coatings Produced by Anodic Oxidation

16. Miscellaneous Coatings
Vitreous Enamel Coatings
Thermoplastics
Temporary Protectives

17. Conditioning the Environment
Boiler and Feed-water Treatment
Conditioning the Atmosphere to Reduce Corrosion
Corrosion Inhibition: Principles and Practice
The Mechanism of Corrosion Prevention by Inhibitors

18.Non-Metallic Materials
Carbon
Glass and Glass-ceramics
Vitreous Silica
Glass Linings and Coatings
Stoneware
Plastics and Reinforced Plastics
Rubber and Synthetic Elastomers
Corrosion of Metals by Plastics
Wood
The Corrosion of Metals by Wood

19. Corrosion Testing, Monitoring and Inspection
Corrosion Testing
Appendix - Removal of Corrosion Products
Appendix - Standards for Corrosion Testing
The Potentiostat and its Applications to Corrosion Studies
Corrosion Monitoring and Inspection
Inspection of Paints and Painting Operations

20. Electrochemistry and Metallurgy Relevant to Corrosion
Outline of Electrochemistry
Outline of Chemical Thermodynamics
The Potential Difference at a Metal/Solution Interface
Outline of Structural Metallurgy Relevant to Corrosion

21. Useful Information
Tables
Glossary of Terms
Symbols and Abbreviations

Basic Concepts of Corrosion

Modern technology has at its disposal a wide range of constructional
materials -metals and alloys, plastics, rubber, ceramics, composites, wood,
etc. and the selection of an appropriate material for a given application is
the important responsibility of the design engineer. No general rules govern
the choice of a particular material for a specific purpose, and a logical decision
involves a consideration of the relevant properties, ease of fabrication,
availability, relative costs, etc. of a variety of materials; frequently the
ultimate decision is determined by economics rather than by properties, and
ideally the material selected should be the cheapest possible that has adequate
properties to fuIfil the specific function.
Where metals are involved, mechanical, physical and chemical properties
must be considered, and in this connection it should be observed that
whereas mechanical and physical properties can be expressed in terms of
constants, the chemical properties of a given metal are dependent entirely on
the precise environmental conditions prevailing during service. The relative
importance of mechanical, physical and chemical properties will depend in
any given case on the application of the metal. For example, for railway
lines elasticity, tensile strength, hardness and abrasion resistance will be of
major importance, whereas electrical conductivity will be of primary significance
in electrical transmission. In the case of heat-exchanger tubes, good
thermal conductivity is necessary, but this may be outweighed in certain
environments by chemical properties in relation to the aggressiveness of the
two fluids involved - thus although the thermal conductivity of copper is
superior to that of aluminium brass or the cupronickels, the alloys are preferred
when high velocity sea water is used as the coolant, since copper has
very poor chemical properties under these conditions.
While a metal or alIoy may be selected largely on the basis of its mechanical
or physical properties, the fact remains that there are very few applications
where the effect of the interaction of a metal with its environment can
be completely ignored, although the importance of this interaction will be
of varying significance according to circumstances; for example, the slow
uniform wastage of steel of massive cross section (such as railway lines or
sleepers) is of far less importance than the rapid perforation of a buried steel
pipe or the sudden failure of a vital stressed steel component in sodium
hydroxide solution.

The effect of the metal/environment interaction on the environment itself
is frequently more important than the actual deterioration of the metal (see
Section 2.7). For instance, lead pipes cannot be used for conveying plumbosolvent
waters, since a level of lead > 0.1 p.p.m. is toxic; similarly, galvanised
steel may not be used for certain foodstuffs owing to the toxicity of
zinc salts (see Section 2.8). In many chemical processes selection of a particular
metal may be determined by the need to avoid contamination of the
environment by traces of metallic impurities that would affect colour or taste
of products or catalyse undesirable reactions; thus copper and copper alloys
cannot be used in soap manufacture, since traces of copper ions result in
coloration and rancidification of the soap. In these circumstances it will be
essential to use unreactive and relatively expensive metals, even though the
environment would not result in the rapid deterioration of cheaper metals
such as mild steel. A further possibility is that contamination of the environment
by metals’ ions due to the corrosion of one metal can result in the
enhanced corrosion of another when the two are in contact with the same
environment. Thus the slow uniform corrosion of copper by a cuprosolvent
domestic water may not be particularly deleterious to copper plumbing, but
it can result in the rapid pitting and consequent perforation of galvanised
steel and aluminium that subsequently comes into contact with the coppercontaining
water (Sections 4.1, 4.2 and 4.7).
Finally, it is necessary to point out that for a number of applications
metals are selected in preference to other materials because of their visual
appearance, and for this reason it is essential that brightness and reflectivity
are retained during exposure to the atmosphere; stainless steel is now widely
used for architectural purposes, and for outdoor exposure the surface must
remain bright and rust-free without periodic cleaning (Section 3.3). On the
other hand, the slow-weathering steels, which react with the constituents of
the atmosphere to form an adherent uniform coating of rust, are now being
used for cladding buildings (Section 3.2), in spite of the fact that a rusty surface
is usually regarded as aesthetically unpleasant.
The interaction of a metal or alloy (or a non-metallic material) with its
environment is clearly of vital importance in the performance of materials
of construction, and the fact that the present work is largely confined to a
detailed consideration of such interactions could create the impression that
this was the sole factor of importance in materials selection. This, of course,
is not the case although it is probably true to say that this factor is the one
that is the most neglected by the design engineer.

Definitions of Corrosion

In the case of non-metallic materials, the term corrosion invariably refers
to their-deterioration from chemical causes, but a similar concept is not
necessarily applicable to metals. Many authorities consider that the term
metallic corrosion embraces all interactions of a metal or alloy (solid or
liquid) with its environment, irrespective of whether this is deliberate and
beneficial or adventitious and deleterious. Thus this definition of corrosion,
which for convenience will be referred to as the transformation definition, will include, for example, the deliberate anodic dissolution of zinc in
cathodic protection and electroplating as well as the spontaneous gradual
wastage of zinc roofing sheet resulting from atmospheric exposure.
On the other hand, corrosion has been defined’ as ’the undesirable
deterioration’ of a metal or alloy, i.e. an interaction of the metal with its
environment that adversely affects those properties of the metal that are to
be preserved. This definition-which will be referred to as the deterioration
definition - is also applicable to non-metallic materials such as glass, concrete,
etc. and embodies the concept that corrosion is always deleterious.
However, the restriction of the definition to undesirable chemical reactions
of a metal results in anomalies which will become apparent from a consideration
of the following examples.
Steel, when exposed to an industrial atmosphere, reacts to form the reaction
product rust, of approximate composition Fe,O, - HzO, which being
loosely adherent does not form a protective barrier that isolates the metal
from the environment; the reaction thus proceeds at an approximately linear
rate until the metal is completely consumed. Copper, on the other hand
forms an adherent green patina, corresponding approximately with bronchantite,
CuSO, - 3Cu(OH), , which is protective and isolates the metal
from the atmosphere. Copper roofs instalIed 200 years ago are still performing
satisfactorily, and it is apparent that the formation of bronchantite is
not deleterious to the function of copper as roofing material-indeed, in
this particular application it is considered to enhance the appearance of the
roof, although a similar patina formed on copper water pipes would be
aesthetically objectionable.
The rapid dissolution of a vessel constructed of titanium in hot 40Vo
H, SO, with the formation of Ti4+ aquo cations conforms with both definitions
of corrosion, but if the potential of the metal is raised (anodic protection)
a thin adherent protective film of anatase, TiO,, is formed, which
isolates the metal from the acid so that the rate of corrosion is enormously
decreased. The formation of this very thin oxide film on titanium, like that
of the relatively thick bronchantite film on copper, clearly conforms with the
transformation definition of corrosion, but not with the deterioration definition,
since in these examples the rate and extent of the reaction is not
significantly detrimental to the metal concerned. Again, magnesium, zinc or
aluminium is deliberately sacrificed when these metals are used for the
cathodic protection of steel structures, but as these metals are clearly not
required to be maintained as such, their consumption in this particular
application cannot, according to the deterioration, be regarded as corrosion.
Furthermore, corrosion reactions are used to advantage in technological
processes such as pickling, etching, chemical and electrochemical polishing
and machining, etc.
The examples already discussed lead to the conclusion that any reaction
of a metal with its environment must be regarded as a corrosion process
irrespective of the extent of the reaction or of the rates of the initial and
subsequent stages of the reaction. It is not illogical, therefore, to regard
passivity, in which the reaction product forms a very thin protective film that
controls rate of the reaction at an acceptable level, as a limiting case of a corrosion
reaction. Thus both the rapid dissolution of active titanium in 40%
H,SO, and the slow dissolution of passive titanium in that acid must be regarded as corrosion processes, even though the latter will not be detrimental
to the metal during the anticipated life of the vessel.
It follows that in deciding whether the corrosion reaction is detrimental to
a metal in a given application, the precise form of attack on the metal
(general, intergranular, etc.), the nature of the reaction products (protective
or non-protective), the velocity and extent of the reaction and the location
of the corrosion reaction must all be taken into account. In addition, due
consideration must be given to the effect of the corrosion reaction on the
environment itself. Thus corrosion reactions are not always detrimental, and
our ability to use highly reactive metals such as aluminium, titanium, etc. in
aggressive environments is due to a limited initial corrosion reaction, which
results in the formation of a rate-controlling corrosion product. Expressions
such as ‘preventing corrosion’, ‘combating corrosion’ or even ‘fighting corrosion’
are misleading; with the majority of metals corrosion cannot be
avoided and ‘corrosion control’ rather than ‘prevention’ is the desired goal.
The implication of ‘control’ in this context is that (a) neither the form, nor
the extent, nor the rate of the corrosion reaction must be detrimental to the
metal used as a constructional material for a specific purpose, and (b) for
certain applications the corrosion reaction must not result in contamination
of the environment. The scope of corrosion control is considered in more
detail in the Introduction to Volume 2, but it is relevant to mention here that
it must involve a consideration of materials, availability, fabrication, protective
methods and economics in relation to the specific function of the metal
and its anticipated life, At one extreme corrosion control in certain
environments may be effected by the use of thick sections of mild steel
without any protective system, at the other the environmental conditions
prevailing may necessitate the use of platinum.
The scope of the term ‘corrosion’ is continually being extended, and Fontana
and Staehle have stated3 that ‘corrosion will include the reaction of
metals, glasses, ionic solids, polymeric solids and composites with environments
that embrace liquid metals, gases, non-aqueous electrolytes and other
non-aqueous solutions’.
Vermilyea, who has defined corrosion as a process in which atoms or
molecules are removed one at a time, considers that evaporation of a metal
into vacuum should come within the scope of the term, since atomically it
is similar to other corrosion processes4.
Evans’ considers that corrosion may be regarded as a branch of chemical
thermodynamics or kinetics, as the outcome of electron affinities of metals
and non-metals, as short-circuited electrochemical cells, or as the demolition
of the crystal structure of a metal.
These considerations lead to the conclusion that there is probably a
need for two definitions of corrosion, which depend upon the approach
adopted:
1. Definition of corrosion in the context of Corrosion Science: the reaction
of a solid with its environment.
2. Definition of corrosion in the context of Corrosion Engineering: the
reaction of an engineering constructional metal (material) with its
environment with a consequent deterioration in properties of the metal
(material).

Methods of Approach to Corrosion Phenomena

The effective use of metals as materials of construction must be based on an
understanding of their physical, mechanical and chemical properties. These
last, as pointed out earlier, cannot be divorced from the environmental conditions
prevailing. Any fundamental approach to the phenomena of corrosion
must therefore involve consideration of the structural features of the
metal, the nature of the environment and the reactions that occur at the
metal/environment interface. The more important factors involved may be
summarised as follows:
1. MetaZ- composition, detailed atomic structure, microscopic and
macroscopic heterogeneities, stress (tensile, compressive, cyclic), etc.
2. Environment - chemical nature, concentrations of reactive species and
deleterious impurities, pressure, temperature, velocity, impingement,
etc.
3. Metd/environment interface - kinetics of metal oxidation and dissolution,
kinetics of reduction of species in solution; nature and location of
corrosion products; film growth and film dissolution, etc.
From these considerations it is evident that the detailed mechanism of
metallic corrosion is highly complex and that an understanding of the
various phenomena will involve many branches of the pure and applied
sciences, e.g. metal physics, physical metallurgy, the various branches of
chemistry, bacteriology, etc. although the emphasis may vary with the particular
system under consideration. Thus in stress-corrosion cracking (see
Section 8.1) emphasis may be placed on the detailed metallurgical structure
in relation to crack propagation resulting from the conjoint action of corrosion
at localised areas and mechanical tearing, while in underground corrosion
the emphasis may be on the mechanism of bacterial action in relation
to the kinetics of the overall corrosion reaction (see Section 2.6).
Although the mechanism of corrosion is highly complex the actual control
of the majority of corrosion reactions can be effected by the application of
relatively simple concepts. Indeed, the Committee on Corrosion and
Protection6 concluded that ‘better dissemination of existing knowledge’ was
the most important single factor that would be instrumental in decreasing the
enormous cost of corrosion in the U.K.
Corrosion as a Chemical Reaction at a MetaVEnvironment lntertace
As a first approach to the principles which govern the behaviour of metals
in specific environments it is preferable for simplicity to disregard the
detailed structure of the metal and to consider corrosion as a heterogeneous
chemical reaction which occurs at a metalhon-metal interface and which
involves the metal itself as one of the reactants (cf. catalysis). Corrosion can
be expressed, therefore, by the simple chemical reaction:
aA + bB = CC + dD
where A is the metal and B the non-metal reactant (or reactants) and C and
D the products of the reaction. The nonmetallic reactants are frequently referred to as the environment although it should be observed that in a complex
environment the major constituents may play a very subsidiary role in
the reaction. Thus in the ‘atmospheric’ corrosion of steel, although nitrogen
constitutes approximately 75% of the atmosphere, its effect, compared with
that of moisture, oxygen, sulphur dioxide, solid particles, etc. can be disregarded
(in the high-temperature reaction of titanium with the atmosphere,
on the other hand, nitrogen is a significant factor).
One of the reaction products (say, C) will be an oxidised form of the metal,
and D will be a reduced form of the non-metal- C is usually referred to as
the corrosion product, although the term could apply equally to D. In its
simplest form, reaction 1.1 becomes
aA + bB = CC . . .(1.2)
e.g. 4Fe + 30, = 2Fe20,
where the reaction product can be regarded either as an oxidised form of the
metal or as the reduced form of the non-metal. Reactions of this type which
do not involve water or aqueous solutions are referred to as ‘dry’ corrosion
reactions.
The corresponding reaction in aqueous solution is referred to as a ‘wet’
corrosion reaction, and the overall reaction (which actually occurs by a series
of intermediate steps) can be expressed as
4Fe + 2H20 + 302 = 2Fe20, .H,O . .(1.3)
Thus in all corrosion reactions one (or more) of the reaction products will
be an oxidised form of the metal, aquo cations (e.g. Fe2+ (as.), Fe3+ (as.)),
aquo anions (e.g. HFeOAaq.), FeOi- (as.)), or solid compounds (e.g.
Fe(OH),, Fe,O.,, Fe,O,-H,O, Fe,O, .H,O), while the other reaction product
(or products) will be the reduced form of the non-metal. Corrosion may
be regarded, therefore, as a heterogeneous redox reaction at a metalhonmetal
interface in which the metal is oxidised and the non-metal is reduced.
In the interaction of a metal with a specific non-metal (or non-metals) under
specific environmental conditions, the chemical nature of the non-metal, the
chemical and physical properties of the reaction products, and the environmental
conditions (temperature, pressure, velocity, viscosity, etc.) will
clearly be important in determining the form, extent and rate of the reaction.

Environment

Environments are considered in detail in Chapter 2, but some examples
of the behaviour of normally reactive and non-reactive metals in simple
chemical solutions will be considered here to illustrate the fact that corrosion
is dependent on the nature of the environment; the thermodynamics of the
systems and the kinetic factors involved are considered in Sections 1.4 and
1.9.
Gold is stable in most strong reducing acids, whereas iron corrodes
rapidly, yet finely divided gold can be quickly dissolved in oxygenated
cyanide solutions which may be contained in steel tanks. A mixture of
caustic soda and sodium nitrate can be fused in an iron or nickel crucible,
whereas this melt would have a disastrous effect on a platinum crucible. Copper is relatively resistant to dilute sulphuric acid but will corrode if
oxygen or oxidising agents are present in the acid, whereas austenitic
stainless steels are stable in this acid only if oxygen or other oxidising agents
are present. Iron will corrode rapidly in oxygenated water but extremely
slowly if all oxygen is removed; if, however, oxygen is brought rapidly and
simultaneously to all parts of the metal surface the rate will become very
slow, owing to the formation of a protective oxide film. Lead will dissolve
rapidly in nitric acid, more slowly in hydrochloric acid, and very slowly in
sulphuric acid. These examples show that the corrosion behaviour of a metal
cannot be divorced from the specific environmental conditions prevailing,
which determine the rate, extent (after a given period of time) and form of
the corrosion process.

Metal

Heterogeneities associated with a metal have been classified in Table 1.1 as
atomic (see Fig. 1. l), microscopic (visible under an optical microscope), and
macroscopic, and their effects are considered in various sections of the present
work. It is relevant to observe, however, that the detailed mechanism
of all aspects of corrosion, e.g. the passage of a metallic cation from the
lattice to the solution, specific effects of ions and species in solution in accelerating
or inhibiting corrosion or causing stress-corrosion cracking, etc.
must involve a consideration of the detailed atomic structure of the metal or
alloy.
The corrosion behaviour of different constituents of an alloy is well
known, since the etching techniques used in metallography are essentially
corrosion processes which take advantage of the different corrosion rates of
phases as a means of identification, e.g. the grain boundaries are usually
etched more rapidly than the rest of the grain owing to the greater reactivity
of the disarrayed metal Macroscopic heterogeneities, e.g. crevices, discontinuities in surface films,
bimetallic contacts etc. will have a pronounced effect on the location and the
kinetics of the corrosion reaction and are considered in various sections
throughout this work. Practical environments are shown schematically in
Fig. 1.3, which also serves to emphasise the relationship between the detailed
structure of the metal, the environment, and external factors such as stress,
fatigue, velocity, impingement, etc.

Types of Corrosion

Corrosion can affect the metal in a variety of ways which depend on its
nature and the precise environmental conditions prevailing, and a broad
classification of the various forms of corrosion in which five major types
have been identified, is presented in Table 1.2. Thus an 18Cr-8Ni stainless
steel will corrode uniformly during polishing, active dissolution or passivation,
but wiII corrode Iocally during intergranular attack, crevice corrosion
or pitting; in certain circumstances selective attack along an ‘active path’ in
conjunction with a tensile stress may lead to a transgranular fracture. Types
of corrosion are dealt with in more detail in Appendix 1.1A.

Tabk 1.2 Types of corrosion
Type Characteristic Examples
1. Uniform (or All areas of the maal corrode
at the same (or similar) rate almost uniform)
2. Localised
3. Pitting
Certain areas of the metal
surface corrode at higher
rates than others due to
‘heterogeneities’ in the
metal, the environment or in
the geometry of the
structure as a whole. Attack
can range from being
slightly localised to pitting
Highly localised attack at
specific areas resulting in
small pits that penetrate into
the metal and may lead to
perforation
(usually the most active) is
selectively removed from an
alloy
due to the synergistic action
of a mechanical factor and
corrosion
4. Selective dissolution One component of an alloy
5. Conjoint action of
corrosion and a
mechanical factor
Localised attack or fracture
Oxidation and tarnishing;
active dissolution in acids;
anodic oxidation and
passivity; chemical and
electrochemical polishing;
atmospheric and immersed
corrosion in certain cases
Crevice corrosion; filiform
corrosion; deposit attack;
bimetallic corrosion;
intergranular corrosion;
weld decay
Pitting of passive metals such
as the stainless steels,
aluminium alloys, etc., in
the presence of specific ions,
e.g. C1- ions
Dezincification;
dealuminification;
graphitisation
Erosion - corrosion, fretting
corrosion, impingement
attack, cavitation damage;
stress corrosion cracking,
hydrogen cracking,
corrosion fatigue

Ideally, the metal selected, or the protective system applied to the metal,
should be such that no corrosion occurs at all, but this is seldom technologically
or economically feasible. It is necessary, therefore, to tolerate a
rate and a form of corrosion that will not be significantly detrimental to the
properties of the metal during its anticipated life. Thus, providing the corrosion
rate is known, the slow uniform corrosion of a metal can frequently be
allowed for in the design of the structure; for example, in the case of a metal
that shows an active/passive transition the rate of corrosion in the passive
region is usually acceptable whereas the rate in the active region is not. It
follows that certain forms of corrosion can be tolerated and that corrosion
control is possible, providing that the rate and form of the corrosion reaction
are predictable and can be allowed for in the design of the structure.
Pitting is regarded as one of the most insidious forms of corrosion, since
it frequently leads to perforation and to a consequent corrosion failure. In
other cases pitting may result in loss of appearance, which is of major importance
when the metal concerned is used for decorative architectural purposes.
However, aluminium saucepans that have been in service for some
time are invariably pitted, although the pits seldom penetrate the metal, i.e.
the saucepan remains functional and the pitted appearance is of no
significance in that particular application.

certainty how a particular metal or alloy will behave in a specific environment4.
It should be appreciated that the decision to use a particular metal
or alloy in preference to others in a given environment or to employ a particular
protective system is based usually on previous experience and
empirical testing (see Chapter 19) rather than on the application of scientific
knowledge- the technology of corrosion is without doubt in advance of corrosion
science and many of the phenomena of corrosion are not fully
understood. Thus the phenomena of passivity which was first observed by
Faraday in 1836 is still a subject of controversy, the specific effect of certain
anions in causing stress-corrosion cracking of certain alloy systems is not
fully understood, and dezincification of brasses can be prevented by additions
of arsenic (or other elements such as antimony or phosphorus) but no
adequate theory has been submitted to explain the action of these elements
(see Section 4.2).
An understanding of the basic principles of the science of metallic corrosion
is clearly vital for corrosion control, and as knowledge of the subject
advances the application of scientific principle rather than an empirical
approach may be used for such purposes as the selection of corrosion
inhibitors, formulation of corrosion-resisting alloys, etc.
Terminology
The classification given in Table 1.2 is based on the various forms that
corrosion may take, but the terminology used in describing corrosion
phenomena frequently places emphasis on the environment or cause of
attack rather than the form of attack. Thus the broad classification of
corrosion reactions into ‘wet’ or ‘dry’ is now generally accepted, and the
nature of the process is frequently made more specific by the use of an
adjective that indicates type or environment, e.g. concentration - cell corrosion,
crevice corrosion, bimetallic corrosion and atmospheric corrosion,high-temperature corrosion, sea-water corrosion, etc. Alternatively, the
phenomenon is described in terms of the corrosion product itself -
tarnishing, rusting, green rot. The terminology used in corrosion is given in
Table 1.3 and is considered in more detail in Appendix 1.1A.

Appendix- Classification of
Corrosion Processes

Existing Classifications

A logical and scientific classification of corrosion processes, although
desirable, is by no means simple, owing to the enormous variety of corrosive
environments and the diversity of corrosion reactions, but the broad classification
of corrosion reactions into ‘wet’ or ‘dry’ is now generally accepted,
and the terms are in common use. The term ‘wet’ includes all reactions in
which an aqueous solution is involved in the reaction mechanism; implicit
in the term ‘dry’ is the absence of water or an aqueous solution.
These terms are evidently ambiguous; for example, it is not always clear
whether ‘wet’ is confined to aqueous solutions-the ‘wetting’ of solids by
mercury indicates that liquid-metal corrosion should be classified as ‘wet’.
Even if the term is restricted to aqueous solutions, the difficulty arises that
the mechanism of growth of magnetite scale during the reaction of the
interior of a boiler drum with dilute caustic soda at high temperatures and
pressures is best interpreted in terms of a ‘dry’ corrosion process. Similar
considerations apply to the reactions of aluminium and zirconium with hightemperature
water.
Considering oxidation as a typical ‘dry’ reaction it follows from Fig. 1 .Ala
that at the interfaces:
M + (Mz+O/O) + z(eO/O)
where Mz+ 0 is an interstitial metal ion, e0 an interstitial electron and /O
indicates the metal/oxide interface (Section 1 A).
If the metal dissolves to enter a vacant site, then
M * (Mz+O/O + zeO/O)
where MZ+O represents a cation vacancy and e 0 a positive hole.
At the gadoxide interface the O2 gas ionises
(fO,/ads.) + 2(e/X) (O*-/ads.)
where /X indicates the gadoxide interface.
respectively.
By definition, these interfaces can be considered as anodes and cathodes respectively.

‘Dry Corrosion
These are generally metal/gas or metal/vapour reactions involving nonmetals
such as oxygen, halogens, hydrogen sulphide, sulphur vapour, etc.
and oxidation, scaling and tarnishing are the more important forms. A
characteristic of these reactions is that the initial oxidation of the metal,
reduction of the non-metal, and formation of compound must occur at one
and the same place at the metahon-metal interface. Should the compound
be volatile or discontinuous, further interaction at the interface (or through
a thin film of constant thickness) is possible and in most cases the reaction
rate will tend to remain constant with time (linear law). If the film is continuous
it will present a barrier to the reactants and further interaction will
necessitate passage of the reactants through the film by (a) diffusion of the
non-metal or (a) diffusion and migration of ions of the reactants. The
detailed mechanisms of these reactions are considered in Sections 1.8-1.10,
but it is appropriate to observe that the formation of a continuous film of
reactant product at a metalhon-metal interface will result in a growth rate
which, when the film becomes sufficiently thick to be rate determining,
decreases as the film thickens, Le. parabolic, logarithmic, asymptotic, cubic,
etc.

‘Wet’ Conosion

In ’wet’ corrosion the oxidation of the metal and reduction of a species in
solution (electron acceptor or oxidising agent) occur at different areas on the metal surface with consequent electron transfer through the metal from the
anode (metal oxidised) to the cathode (electron acceptor reduced); the
thermodynamically stable phases formed at the metalholution interface
may be solid compounds or hydrated ions (cations or anions) which may be
transported away from the interface by processes such as migration, diffusion
and convection (natural or forced). Under these circumstances the reactants
will not be separated by a barrier and the rate law will tend to be linear.
Subsequent reaction with the solution may result in the formation of a stable
solid phase, but as this will form away from the interface it will not be
protective - the thermodynamically stable oxide can affect the kinetics of the
reaction only if it forms a film or precipitates on the metal surface (see Sections
1.4 and 1.5).
Further points which distinguish ‘wet’ from ‘dry’ corrosion are:
1. In ‘wet’ corrosion the metal ions are hydrated- the hydration energy of
most metal ions is very large and thus facilitates ionisation (see Section
1.9).
2. In ‘wet’ corrosion ionisation of oxygen to hydroxyl must involve the
hydronium ion or water.
3. In ‘dry’ corrosion the direct ionisation of oxygen occurs.

Corrosion in Organic Solvents

Corrosion reactions in aggressive organic solvents are becoming a more frequent
occurrence owing to developments in the chemical and petrochemical
industries, and these reactions can lead to the deterioration of the metal and
to undesirable changes in the solvent. This aspect of corrosion has recently
been the subject of an extensive review by Heitz’ who has considered the
mechanisms of the reactions, the similarities between corrosion in organic
solvents and in aqueous solutions, the methods of study and the occurrence
of the phenomenon in industrial processes.

Figure 1 .A2 shows the weight loss against time curve for nickel in various
solvents containing 0.05 wt. 9'0 H,S04 at various temperatures, and illustrates
the unpredictable nature of corrosion in organic solvents. Thus the
corrosion rates in ethanol are far greater than those in the aqueous acid
whereas in acetone the rate is practically zero; even more surprising is the fact
that in acetic acid the addition of 0.05% &SO, actually decreases the corrosion
rate.
Heitz classifies corrosion reactions in organic solvents into
1. Electrochemical reactions, which follow a similar mechanism to those
in aqueous solution.
2. Chemical reactions, which involve direct charge transfer between the
metal atom in the lattice of the metal and the oxidising species.
In the case of electrochemical reactions the partial anodic reaction results
in the formation of a solvated metal cation M:&. , a charged or uncharged
metal complex MX- or a solid compound MX,, where X is a halogen ion,
organic acid anion, etc.
The cathodic partial reactions are as follows:
(a) Reduction of a solvated proton to Hz gas
H,+,,", + e + fH2
(b) Reduction of acidic hydrogen of a proton donor
H A + e + f H , + A -
where A- is a carboxylic acid anion, alcoholate ion, etc.
(c) Reduction of an oxidising gas Y
Y, + zme + zY"-
where Y can be O,, Cl,, F,, Br,, O,, N204, etc.
(d) Reduction of oxidising ions such as Fe3+, Cuz+, MnO, Clog etc. It
is evident from the above that in many systems the reaction of a metal with
an organic solvent follows a mechanism that is similar to the electrochemical
mechanism of corrosion in aqueous solution.
Non-electrochemical processes may be represented by the general
equation
where X is a halogen and M is a divalent metal, e.g. the Grignard reaction
Mg + CH3C1-+ CH3MgCl
A further type of chemical process, which is analogous to hightemperature
corrosion, is the reaction of metals with organic sulphur compounds,
which follow the equation
2M+ 2RSH + 2MS + H, + R,
Heitz quotes a number of case stydies of corrosion of metals in organic
solvents and concludes that the phenomenology indicates no specific
differences from that experienced in aqueous corrosion. Thus general corrosion,
pitting, crevice corrosion, intergranular corrosion, erosion-corrosion
cracking, hydrogen embrittlement, etc. can all occur in organic solvents.
The methods of control also follow that used for corrosion in aqueous solutions, although there are certain differences. Thus cathodic and anodic
protection are seriously limited by the resistivity of the solvent, and paint
coatings deteriorate rapidly in contact with the solvent.
Suggested Classification and Nomenclsture
On a basis of the preceding discussion, the classification and nomenclature
outlined in Table 1 .Al is suggested as a possible alternative to the accepted
classification of corrosion reactions into ‘wet’ and ‘dry’. It is considered that the main types of corrosion reactions can be classified
1. Film-free chemical interaction in which there is direct chemical reaction
of a metal with its environment. The metal remains film-free and there
is no transport of charge.
2. Electrochemical reactions which involve transfer of charge across an
interface. These electrochemical reactions can be further subdivided
into:
(a) Inseparable anode/cathode type (insep. A/C). The anodes and
cathodes cannot be distinguished by experimental methods
although their presence is postulated by theory, i.e. the uniform dissolution of metals in acid*, alkaline or neutral aqueous solutions,
in non-aqueous solution, or in fused salts.
(b) Separable anode/cathode type (sep. A/C). Certain areas of the
metal can be distinguished experimentally as predominantly anodic
or cathodic, although the distances of separation of these areas may
be as small as fractions of a millimetre. In these reactions there will
be a macroscopic flow of charge through the metal.
(c) Interfacial anode/cathode type (interfacial A/C). One entire interface
will be the anode and the other will be the cathode. Thus in
Fig. 1 .Ala the metal/metal oxide interface might be regarded as the
anode and the metal/oxygen interface as the cathode.
It is apparent that, in general, 2(a) and 2(b) include corrosion reactions
which are normally classified as ‘wet’, while 2(c) includes those which are
normally classified as ‘dry’.
The terminology suggested can be illustrated by reference to the corrosion
behaviour of iron:
1. Reaction of iron with oxygen at room temperature or with oxygen or
water at high temperatures - interfacial A/C type.
2. Reaction of iron with oxygenated water or with reducing acidsinseparable
A/C type.
3. Reaction of iron containing a discontinuous magnetite scale with
oxygenated water, crevice corrosion, water-line attack, ‘long-line’ corrosion
of buried iron pipes, etc. -separable A/C type.
Although it is realised that this classification and terminology has certain
limitations, it represents a preliminary attempt to provide a more rational
classification of corrosion processes than that based on ‘wet’ and ‘dry’.
Acknowledgement
Grateful thanks are due to Dr. W. B. Jepson, Dr. M. Pryor and Mr. J. N.
Wanklyn for helpful discussions during the preparation of this Appendix.
L. L. SHREIR

it will be continued...