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Ravindra Pudasaini, FUCHS Product Application Engineering Manager
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How to protect Ferrous Metal Components from Corrosion
Abstract: As we know well that Corrosion can deteriorate the metals physical, chemical,
mechanical and the aesthetical properties; which leads to proliferate economical losses
and EHS issues. The global loss from corrosion is approximately US$ 2.5 Trillion per year
and in China it is US$ 9 Billion/Y. Consequently, protecting the metals from corrosion
becomes very important. By understanding the causes of metal corrosion in various
conditions, its initiation and propagation rate can help to determine the corrosion
prevention technique and stop the corrosion initiation rate thus 25 % of the economic
losses can be retrieved easily. The aim of this article is familiar with the types of corrosion
occurring at various conditions and the key factors affecting the rate of corrosion so that
able to furnish the right solution to protect the metal properly
Ravindra Pudasaini, FUCHS Product Application Engineering Manager
1. Introduction of Corrosion
Corrosion is an irreversible natural phenomenon which attacks metals by chemical or electrochemical
action and converts it into a metallic compound, such as an oxide, hydroxide, or sulfate. The term
“corrosion” is derived from Latin and describes a “chemical change in the material on the surface of a
metal”. The term corrosion can also be applied to all materials like metals, non-metals, ceramics and
polymers therefore in this subject, the term "degradation" is more common. Corrosion degrades the key
properties like Physical, Chemical, Mechanical and Aesthetical of metallic materials.
1.1 Root Cause of Corrosion
As we know that Iron has been manufactured from chemically very stable iron oxide ores so under the
action of oxygen and moisture, the metals have a tendency to revert to its natural state and the corrosion
occurs.
During the metal manufacturing process every metal naturally coated with an oxide layers; we call this a
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“passive layer” which protects metals against further reacting with oxygen. As the oxide layer is started to
rupture as simply; the metal started to corrode as quickly, the stability of oxide layers depends on the type
of metals, e.g. In Aluminum and Zinc the passive layers are very stable thus they do not corrode easily.
Noble metals, such as gold and platinum hardly corrode since they are chemically uncombined in their
natural state.
The iron and its alloy corrode easily because In iron the oxide layer is irregular, fragile and provides very
little protection therefore iron and its alloys need to be protected from corrosion. Corrosion has its roots in
electrochemistry and metallurgy of metals
Before applying the corrosion preventives, we need to understand corrosion profoundly such as how
corrosion happens, when it attacks, how to endorse it etc. After having all these details, we might be able
to take the major steps to protect the metals from corrosion
This article explains in detail on how to select the right methods to protect the metals from the corrosion
occurring in varied conditions
1.2 Mechanism of Corrosion
It is generally acknowledged that corrosion processes are caused by the violation of the oxide layer, which
leads to initiation of chemical reaction (corrosion) and ion flow. Due to the flow of ions electrochemical
cell is formed and oxidation takes place in one area called the Anode, travel through a metallic path and
are consumed through a different chemical reaction in another area called the Cathode. Electrochemical
Reaction Corrosion are the most frequent types of corrosion
In order to occur electrochemical reactions, four components anode, cathode electron path and
electrolyte as in above picture, must be present and active.
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⚫ Anode
In an electrochemical cell the anode is the site where electrons are produced through the chemical
activity or metal loss and corrosion occur. Anodic reactions give up electrons (Oxidation half reaction).
The electrons in the metal but are free to move in response to voltage gradients. Metal loses electrons
and migrates from the metal surface through the environment.
⚫ Cathode
In an electrochemical cell the cathode is the site where electrons are consumed. For each electron that is
produced at an anodic site must be consumed at a cathodic site. Cathodic reactions accept electrons
(Reduction half reaction) so metal loss and corrosion never occur in cathodic sites
⚫ Metallic Path (Electrical connection)
In order to flow the electrons from the anodic sites to cathodic sites, electrons need to migrate through an
electrical connection called metallic path ((wire, metal wall, etc.). This migration occurs due to a voltage
difference between the anodic and cathodic reactions. In some cases, the electron path is the corroding
metal itself, in other cases, the electron path is through an external electrical path.
⚫ Electrolyte
The electrolyte is the medium that facilitates the flow of electrons (electric current) between the anode
and cathode. Electrolyte can be Soil, Moisture, Water and contaminants. Positive ions tend to migrate
away from anodic areas and to cathodic areas. Negative ions tend to migrate away from cathodic areas
to anodic areas.
1.3 Chemical Reaction in Electrochemical cell
In the anodic reaction, metal goes into solution as an ion. The reaction is generally written as:
M Mn+ + ne-
Where M is a metallic element, e- is an electron and n is the valence of the metal as an ion
In the cathodic reaction, electrons provided by the anode, flow through the metal until they reach the
cathode where they can be combined with positively charged ions. In acidic solutions this reaction is:
2H+ + 2 e- 2H H2(gas)
⚫ In neutral solutions or in the present of Oxygen the reaction is:
O2 + 2H2O + 4 e- 4 OH-
The hydroxyl ions combine with the ferrous ions to form metal hydroxide
Men+ + 4 OH- 2 M(OH)2
⚫ In the presence of Water and Oxygen, the metal hydroxide is further oxidized to form M2O3
4M(OH)2+O2+H2O 4 M(OH)3
2M(OH) 3 M2O3 + 2H2O
⚫ In the presence of Chloride
M Mn+ + ne- (dissolution of iron)
The electrons given up by the anode flow to the cathode where they are discharged in the
cathodic reaction: 1/2O2 + H2O + 2e- = 2(OH-)
The positively charged pit attracts negative ions of chlorine Cl- increasing acidity of the
electrolyte according to the reaction: MCl2 + 2H2O = M(OH)2 + 2HCl
⚫ In the presence of Sulfides
M + SO2 + O2 → MSO4
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4M + 2 H2O+ 3O2 → 4 MOOH
Both the anodic and cathodic reactions must occur simultaneously for a corrosion process to proceed. If
both reactions will not happen then a charge builds up and the corrosion process stops. The anodic
reaction is generally the simple case of a metal going into solution. However, a variety of cathodic
reactions are encountered depending on the conditions of the process involved.
2. Significance of Corrosion protection
As we know well that Corrosion can deteriorate the metals physical, chemical, mechanical and the
aesthetical properties; which leads to proliferate economical losses and EHS issues. The global loss from
corrosion is approximately US$ 2.5 Trillion per year and in China it is US$ 9 Billion/Y. Consequently,
protecting the metals from corrosion becomes very important. By understanding the causes of metal
corrosion in various conditions, its initiation and propagation rate can help to determine the corrosion
prevention technique and stop the corrosion initiation rate thus 25 % of the economic losses can be
retrieved easily.
The aim of this article is familiar with the types of corrosion occurring at various conditions and the key
factors affecting the rate of corrosion so that able to furnish the right solution to protect the metal properly
2.1 Types of Corrosion
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Different Types of Corrosion
2.2 Factors affecting Corrosion Rate
Two key factors can be considered for the initiation and propagation of corrosion rate
Size and Shape of the metal components
⚫ Exposed area: As narrower or smaller the area, the corrosion rate increases as quickly
⚫ Time of exposure: the exposure time is as longer, the corrosion rate increases as faster
Environmental Factors (Hostile Environment）
⚫ Acidic environment, higher the acidic environment, vastly the corrosion rate
⚫ Salty environment, higher the salty environment, faster the corrosion rate
⚫ Temperature: higher the temperature, faster the corrosion propagation
⚫ Moisture: Higher the moisture or humidity, higher the corrosion rate
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⚫ As the pH is decreasing (acidity increase), the corrosion rate is increasing. This is because low pH
solutions accelerate corrosion by providing hydrogen ions. Hydrogen attacks and damages the
surface of steel and increases the material loss, i.e. corrosion
⚫ The higher the temperature, the higher the corrosion rate, temperature is accelerating the corrosion
rate since temperature depends on the chemical reactivity of metallic materials
⚫ The chloride concentration also increases the corrosion rate in the Figure. The chloride ions increase
the acidity on metals. since in the presence of this ion, a passivity breakdown process takes place
due to which Chloride ions slowly penetrate on the surface, at which the protective film is destroy
and the steel begins to corrode. Chloride penetration in metal is due to the diffusion and capillary
absorption mechanisms.
2.3 Recognizing various stages of corrosion by its appearance
In the ferrous metal any types of corrosion (Uniform and Localized corrosion) might be occurred, the
corrosion types depend on the conditions confront by metals
⚫ The first stage of corrosion is a discoloration of the metal, usually noticed when begins to
look fade. When we check in an electronic microscope or sometimes by naked eyes also, the
components surface found dull and it is the beginning stages of corrosion
⚫ The second stage is the presence of visible Iron oxide in the form of a gray powder or crust on
the surface of the components. Some types of corrosion like inner granular corrosion, the first and
second stages may only be detected by precision measurement of the component or by high tech
non-destructive testing methods, such as ultrasonic tests.
⚫ The third stage of corrosion exists when the crusty oxidation is removed to reveal severe
pitting or holes in the metal surface, or cracks and de-lamination caused by corrosion.
⚫ Fourth and most advanced stage of corrosion: Rust represents corrosion and decay that
have developed to a point at which the base metal has been completely penetrated and removed.
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3. Corrosion protection Methods
Corrosion protection method is based on the principle of “Prevention is better than cure”
There are two key types of corrosion protection method, Permanent and Temporary but we focus only on
Temporary methods which is very useful, effective and economic to the manufacturing industries
Among the various methods to avoid or prevent destruction or degradation of metal surface, the
temporary corrosion inhibitor is one of the best know methods of corrosion protection and one of the most
useful in the industry. This method is popular due to low cost and feasible in auto component industries
Historically, inhibitors had great acceptance in the industries due to excellent anti corrosive proprieties.
But many showed up as a secondary effect, damage the environment. Thus, the scientific community is
searching for environment friendly inhibitors, like the organic inhibitors free of Barium is preferred but
Sodium and Calcium is acceptable
3.1 Corrosion Protection Mechanism:
The purpose of corrosion protection method is to protect the metal surface from air, moisture, dust, sweat,
types atmospheric effects and prevent the oxidation of metal by applying proper corrosion protection
methods
Before corrosion
3 (Voluminous)
Stage 1 (Microscopic)
Stage 2 (Visual)
Stage 4 (Accelerated Decay)
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3.2 Permanent corrosion protection: Permanent corrosion protection is something that is
applied and cannot be easily removed. Paint is a good example of a permanent corrosion preventive.
3.3 Temporary corrosion protection: Many pieces of equipment and components need to be
protected from the point of manufacture to the time when they are to be used. Temporary refers to the
fact that the corrosion protection system is something that can be easily removed with organic solvent
and aqueous alkaline cleaning agents from the metal surface after treatment. It is not designed to difficult
to remove in the same way as permanent coating. Temporary means ‘for a short time; the period can
be anything from 10 minutes to 10 years.
3.4 Temporary Corrosion Protection During Manufacturing, Transportation,
Storage, and Handling
In auto component manufacturing industries, corrosion occurs in inter-stages and transportation due to
which more time is needed to handling customer complains; which leads to potential loss of credibility,
increases rework and generates delay of delivery. Any methods apply to remove the corrosion and
restore the components to its original quality (dimensional accuracy and tolerance) is difficult. Therefor
the best way is to apply the proper corrosion protection to protect the components from direct and
indirect losses from corrosion.
Corrosion can appear within hours or days when exposed to variety of differing corrosive environments
(Indoor, outdoor, Marine, under effect of direct sunlight, chemical environment in the industries, humidity,
moisture etc.) thus protection of auto components from corrosion has key importance. Corrosion
protection need to be compatible or harmony with later stages like cleaning, greasing, packaging etc.
and also needs to be compatible with paint, sealing and adhesives etc. In many cases hybrid corrosion
protection methods are applying to get the best result such as corrosion preventives with VCI wrapping
and packages
Sometimes, the temporary protective may perform other additional functions, such as serve as pre lube
and as a cleaning fluid. As a pre lube it can be for press forming of steel strip, where the same coating
carries out both the corrosion protection and the lubrication of the forming process. As a cleaner, it may
be used for rinsing or cleaning machined parts, and the film left by the cleaner may serve also as the
temporary protective.
3.5 Types of Temporary Protection
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⚫ Anodic Protection: Anodic protection, made up of chromates, nitrites, molybdates, alkali
phosphates, silicates, and carbonates, act by minimizing the anodic part of the corrosion reaction.
These protectors form an insoluble protective film on anodic surfaces to passivate the steel. Some
anodic protectors, such as nitrites, can cause accelerated corrosion and pitting if they are not used
in large enough quantities.
⚫ Cathodic Protection: Cathodic protection, consisting of zinc, salts of antimony, magnesium,
manganese, and nickel, form an insoluble film on the cathodic surfaces of the steel. They are usually
less effective than anodic protectors but are also safer.
⚫ Organic protection: Organic protections, including amines, esters, and sulfonates, block both
the anodic and cathodic reaction on the entire surface of the metal (Virmani and Clemena 1998).
3.6 Preparation phases before applying temporary corrosion protection
⚫ Cleaning
Before applying the corrosion protection fluids, every component should undergo cleaning process to
remove all kinds of dirt particles, manufacturing residues, contaminants and fingerprints. At the same
time, we must need to take care that Cleaning agents and methods do not initiate any additional
residues and corrosion risks
⚫ Drying
After cleaning, the components and its surfaces need to be dry before applying the corrosion protection
fluids. Therefor drying of components become very important. Drying the components with proper
temperature and time need to adjust by types of corrosion protection fluids is going to use in next process
and its application. Normally the corrosion protection fluids are applying when components are at room
temperature by maintaining the homogenous corrosion protection fluid layers on the components. As the
drying temperature is higher and the time is longer, as it takes longer time to the components to cool down
to the room temperature and it affects the next application and the packaging of the components
⚫ Acclimatization & Compatibility
Compatibility of the fluids and acclimatization of the components at ambient room or environmental
conditions need to be done prior to apply corrosion protection methods. Cleaning agents and the corrosion
protection fluids have key importance before applying the corrosion protection. Incompatibility of different
fluids can cause sticky, oil bleeding and residues which leads to corrosion after packaging of few weeks
or months. For acclimatization, the core and surface temperatures of the components being packaged
should be in equilibrium with the temperature of their surroundings. Large temperature differences can
cause serious problems after the components have been packaged. The greatest of these is condensation
forming inside the barrier layer before the active agents can take effect.
3.7 Corrosion protection fluids application methods by Types
Preventing temporary corrosion is an essential strategy for winning the battle against material loss due to
the electrochemical and chemical deterioration of metals in manufacturing processes, transportation and
short-long term storages. The choice of an appropriate corrosion preventive should be done while keeping
the subsequent stages of manufacturing, assembly or end use in mind.
Depends on the application, Corrosion protection types and components shape &size three ways of
applications are available for temporary corrosion protection fluids.
Ravindra Pudasaini, FUCHS Product Application Engineering Manager
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⚫ Smearing the Metal Surfaces with Brush
This method is applicable for high viscous and oil type corrosion protection fluids. Sometimes components
with hard to reach surfaces admit the smearing methods for the solvent based fluids. For waterborne
fluids, brushes made of polyester or nylon are used. For very thick primers, brushes with round bristles
are used. For varnishes, rectangular brushes are useful. The brush method is time-consuming and
inefficient for large work volumes. The smear method is another manual method and is used for locations
where other methods are not feasible
⚫ Spraying the Metal Components
For Small auto parts and metal components solvent based corrosion protection fluids are recommended
and the spray method is selected. The spray technique has the advantages of providing a uniform
application and low wastage due to the thin oil thickness. Various types of spray systems available but
automatic spray methods are recommended for a larger volume of components.
⚫ Dipping Method
Dipping ensures excellent oil thickness on the components as well as very effective and efficient method.
Normally dipping method is suggested for the big components and higher viscosity fluids, but it is
beneficial for all kinds of corrosion protection fluids. However, it requires more space for the bath also the
fluids need to be maintained frequently and properly
3.8 Applying proper methods by Corrosion Protection Fluids Types
Water Based
Method: Both Dipping & Spraying
Needs to care: Concentration, pH control, Drying
Time
Solvent Based
Method: Both Dipping & Spraying
Needs to care: Causing fire, Ventilation, Globes, Dewatering
Oil Based
Method: Dipping & Brushing, Smearing
These are used for inter-stages of manufacturing storage. However, the
chosen protective must be checked for compatibility with seals and packings,
adhesives and nonferrous components.
simple structure and large surface area can choose solvent type
The complex structure with holes choose oil types because still have to
consider when unsealing antirust film can be removed
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4. Product Selection: Ultimately, we need to select the right corrosion protection products for the
components according to the application and the available application in the manufacturing plant
4.1 Normally product can be selected by providing the solutions
⚫ Analyzing the existing process
⚫ Analyzing the existing problem
4.2 Root Cause Analysis of Corrosion
Needs to care: Not Drying easily, Sticking in Fingers Globes
Wax Type
Method: Brushing, Smearing, Dipping
Needs to care: Causing fire, Ventilation, Globes, Drying Time
Wax types are considered superior providers of rust protection because a
protective film can be formed in inaccessible surfaces such as in engine
compartments and car frames.
Volatile Corrosion
Inhibitor (VCI)
Method: Sealed packaged
Needs to care: Sealing tightly
Specially used for packaging the components after applying the
Corrosion protection solvent/oil etc.
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5. Corrosion performance analysis
⚫ Purpose of corrosion testing
For evaluation of the corrosion protective ability of products, accelerated corrosion testing techniques are
used. Metal specimens, properly cleaned and treated with the corrosion protection fluids under scrutiny,
are exposed to the Corrosion tests, and the time required to failure noted in hours thus accelerated
corrosion lab tests become state-of-the-art when it comes to evaluating the performance of materials
5.1 Fresh Product Performance Testing
⚫ Viscosity @ 40ºC
⚫ Density @ 15ºC
⚫ Oil Film Thickness Testing
⚫ Evaporation Rate
⚫ ICP Test (Oil)
⚫ Elemental Analysis
⚫ FTIR Test
⚫ Residue Test
⚫ Dewatering Test
⚫ Conductivity Test for electrostatic application
⚫ Salt Spray Testing
⚫ Humidity Testing
5.2 Applied Corrosion Protection Fluid Analysis
⚫ Viscosity @ 40ºC
⚫ Flash Point
⚫ Density @ 15ºC
⚫ Film Thickness
⚫ Elemental Analysis
⚫ Mechanical Impurities
⚫ Water content
⚫ Humidity Test
⚫ Salt Spray Test
Conclusion: This article mainly focuses on the temporary corrosion, its mechanism,
behavior, types and consequences. By understanding the different modes and its occurring,
the prevention methods are established which is very useful in the industrial use. In
industries the corrosion can damages many metal components which can be prevented by
the proper diagnostic, recognition and analysis of the corrosion. Preventive measure can
be employed before the corrosion occurs. So, the details of root cause analysis with lab
testing methods are also discussed. The aim of this article is to give a clear guidance for
preventing the corrosion.
Ravindra Pudasaini, FUCHS Product Application Engineering Manager
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References：
1. CORROSION: Costs, Causes, and Cures. J.I. Munro, P. Eng, Published in the
WATER AND POLLUTION CONTROL Magazine, February 1978
2. The effect of temperature and pH on the corrosion, rate of carbon steel in 1 M NaCl,
Nervana A. ABD Alameer. Accepted on21/10/2010
3. Corrosion Control, September 1992
4. Effect of ph and chloride concentration on the corrosion of duplex stainless steel,
ARABIAN JOURNAL FOR SCIENCE AND ENGINEERING ·December 2009
5. Guide to Temporary corrosion protection, NPL Management Ltd, Mr Richard Rogers
6. Corrosion Preventive oils, BELGIN Brochure
7. Materials Performance, NACE International, Houston, TX
8. Corrosion and Corrosion Protection, Peter Maa ß
9. Introduction to Cathodic Protection, J. Paul Guyer, P.E., R.A., Fellow
ASCE, Fellow AEI
10. High quality product protection. For transportation by land, air and sea.
Jakob, Schober
11. Corrosion Protection, Arcelor Mittal
12. BUMAX, Brochure, Why did corrosion occurs