Corrosion is the natures’ way of recycling or of returning metals to its lowest energy form. It is an insidious enemy that eats / damages the equipments, structures vehicles, pipelines, buildings, bridges etc.
Corrosion is a very high potential but hidden enemy of Industries, Transport sector and other facilities.

Effects and Cost of Corrosion

The annual worldwide cost of corrosion is estimated to be over $2 to 3 trillion. Yet, the experts believe 25 – 30% could be prevented with proper corrosion protection. Poorly planned projects can lead to a corroded structure needing to be replaced, which is a waste of natural resources and contradictory to global concerns over sustainability. Additionally, the corrosion can lead to safety concerns, loss of life, additional indirect legal / statutory & other costs including tarnishing the reputation. The global cost of corrosion is 2.5 Trillion USD and around 4% of global GDP as per 2022 figures. In case of India, the cost of corrosion is around 5% of GDP and in absolute terms around 6 to 7 lac Crores. As per 2013 figures, the cost of corrosion in India vis-à-vis Global average can be seen below.

Also, the various level of corrosion in India can broadly be put up as map shown here.

 

(Image courtesy : Corrosion-doctors.org)

The most common type of corrosion occurs when it is exposed to oxygen and the presence of water, which creates a red iron oxide commonly called rust. Rust can also effect iron alloys such as steel. The rusting of iron can also occur when iron reacts with chloride in an oxygen-deprived environment, while green rust, which is another type of corrosion, can be formed directly from metallic iron or iron hydroxide.

Types of Corrosion

Uniform Corrosion

This is the most common form of corrosion which usually takes place evenly over large areas of a material’s surface.

Pitting Corrosion

One of the most aggressive forms of corrosion, pitting can be hard to predict, detect or characterise. This localised type of corrosion happens when a local anodic or cathodic point forms a corrosion cell with the surrounding surface. This pit can create a hole or cavity which typically penetrates the material in a vertical direction down from the surface creating worse effects. The pitting corrosion can be caused by damage / break in the oxide film or a protective coating. It can also be caused through non-uniformities in the structure of the metal. This dangerous form of corrosion can cause a structure to fail despite a relatively low loss of metal.

Crevice Corrosion

This type of corrosion occurs in areas where oxygen is restricted such as under washers or bolt heads. It is localised corrosion resulting from difference in the ion concentration between two metal areas. The stagnant ecosystem prevents the circulation of oxygen, resulting in cessation of re-passivation causing building up of stagnant solution moving the pH balance away from neutral. The imbalance between the crevice and the rest of the material contributes to the high rates of corrosion. Crevice corrosion can take place at lower temperatures than pitting corrosion and it can be minimised with proper design.

Intergranular Corrosion

Intergranular corrosion occurs when impurities are present at the grain boundaries which form during solidification of an alloy. It can also be caused by the enrichment or depletion of an alloying element at the grain boundaries. This type of corrosion occurs along or adjacent to the grains, affecting the mechanical properties of the metal despite the bulk of the material being unaffected.

Stress Corrosion Cracking (SCC)

Stress corrosion cracking refers to the growth of cracks due to a corrosive environment which can lead to the failure of ductile metals when subjected to tensile stress, particularly at high temperatures. This type of corrosion is more common among alloys than with pure metals and is dependent on the specific chemical environment whereby only small concentrations of active chemicals are required for catastrophic cracking.

Galvanic Corrosion

This form of corrosion occurs when two different metals with physical or electrical contact are immersed in a common electrolyte (such as salt water) or when a metal is exposed to different concentrations of electrolyte. Where two metals are immersed together, known as a galvanic couple the more active metal (the anode) corrodes fast than the more noble metal (the cathode). The galvanic series determines which metals corrode faster, which is useful when using a sacrificial anode to protect a structure from corrosion.

Prevention of Corrosion

There are different cost effective ways for prevention of corrosion as listed here.

  • Use non-corrosive metals, such as stainless steel or aluminium
  • Ensuring the metal surface stays clean and dry
  • Use drying agents
  • Use a coating or barrier product such as grease, oil, paint or carbon fibre coating
  • Lay a layer of backfill e.g. limestone with underground piping
  • Engaging sacrificial anode providing cathodic protection system

The more details on this topic is covered in our Knowledge sharing file section on our website.

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