CORROSION:-CORROSION:-

TYPESTYPESEFFECTS &EFFECTS &PREVENTION PREVENTION

PRESENTED BY:PRESENTED BY: GAUTAM AHUJAGAUTAM AHUJA 1207535 1207535

What is CorrosionWhat is Corrosion??

Corrosion is the deterioration of materials by Corrosion is the deterioration of materials by chemical interaction with their environment.  The chemical interaction with their environment.  The term corrosion is sometimes also applied to the term corrosion is sometimes also applied to the degradation of plastics, concrete and wood, but degradation of plastics, concrete and wood, but generally refers to metals.generally refers to metals.

TYPES OF CORROSION:-

Uniform corrosion.Uniform corrosion.

Galvanic corrosion.Galvanic corrosion.

Pitting & Crevice corrosion.Pitting & Crevice corrosion.

Stress corrosion cracking.Stress corrosion cracking.

Erosion corrosion.Erosion corrosion.

Microbiologically induced corrosion. Microbiologically induced corrosion.

UNIFORM CORROSION:-UNIFORM CORROSION:-Uniform (or general) Uniform (or general) corrosion refers to the corrosion refers to the relatively uniform reduction relatively uniform reduction of thickness over the of thickness over the surface of a corroding surface of a corroding material. It is relatively easy material. It is relatively easy to measure, predict and to measure, predict and design against this type of design against this type of corrosion damage. While corrosion damage. While uniform corrosion may uniform corrosion may represent only a small represent only a small fraction of industrial fraction of industrial corrosion failures, the total corrosion failures, the total tonnage wasted is generally tonnage wasted is generally regarded as the highest of regarded as the highest of all forms.all forms.

GALVANIC CORROSION:-GALVANIC CORROSION:-Galvanic corrosionGalvanic corrosion is an electrochemical is an electrochemical process in which one metal corrodes process in which one metal corrodes preferentially when in electrical contact preferentially when in electrical contact with a different type of metal and both with a different type of metal and both metals are immersed in an electrolyte. metals are immersed in an electrolyte. When two or more different sorts of metal When two or more different sorts of metal come into contact in the presence of an come into contact in the presence of an electrolyte a galvanic couple is set up as electrolyte a galvanic couple is set up as different metals have different electrode different metals have different electrode potentials. The electrolyte provides a potentials. The electrolyte provides a means for ion migration whereby metallic means for ion migration whereby metallic ions can move from the anode to the ions can move from the anode to the cathode. This leads to the anodic metal cathode. This leads to the anodic metal corroding more quickly than it otherwise corroding more quickly than it otherwise would; the corrosion of the cathodic metal would; the corrosion of the cathodic metal is retarded even to the point of stopping. is retarded even to the point of stopping. The presence of electrolyte and a The presence of electrolyte and a conducting path between the metals may conducting path between the metals may cause corrosion where otherwise neither cause corrosion where otherwise neither metal alone would have corroded.metal alone would have corroded.

PITTING & CREVICE PITTING & CREVICE CORROSION:-CORROSION:-

Pitting Corrosion is the Pitting Corrosion is the localized corrosion of a localized corrosion of a metal surface confined to metal surface confined to a point or small area, that a point or small area, that takes the form of cavities. takes the form of cavities. Pitting is one of the most Pitting is one of the most damaging forms of damaging forms of corrosion. Pitting corrosion. Pitting corrosion forms on corrosion forms on passive metals and alloys passive metals and alloys like stainless steel.The like stainless steel.The resulting pits can become resulting pits can become wide and shallow or wide and shallow or narrow and deep which narrow and deep which can rapidly perforate the can rapidly perforate the wall thickness of a metal.wall thickness of a metal.

STRESS CORROSION CRACKING:-STRESS CORROSION CRACKING:-

It is the cracking induced It is the cracking induced from the combined from the combined influence of tensile stress influence of tensile stress and a corrosive and a corrosive environment. The impact environment. The impact of SCC on a material of SCC on a material usually falls between dry usually falls between dry cracking and the fatigue cracking and the fatigue threshold of that material. threshold of that material. Usually, most of the Usually, most of the surface remains surface remains unattacked, but with fine unattacked, but with fine cracks penetrating into cracks penetrating into the material.the material.

EROSION CORROSION:-EROSION CORROSION:-

Erosion corrosion is an Erosion corrosion is an acceleration in the rate of acceleration in the rate of corrosion attack in metal corrosion attack in metal due to the relative motion of due to the relative motion of a corrosive fluid and a metal a corrosive fluid and a metal surface. The increased surface. The increased turbulence caused by pitting turbulence caused by pitting on the internal surfaces of a on the internal surfaces of a tube can result in rapidly tube can result in rapidly increasing erosion rates increasing erosion rates and eventually a leak. and eventually a leak. Erosion corrosion can also Erosion corrosion can also be aggravated by faulty be aggravated by faulty workmanship.workmanship.

MICROBIAL CORROSION:-MICROBIAL CORROSION:-Microbial corrosion or biological Microbial corrosion or biological corrosion, is the deterioration of corrosion, is the deterioration of metals as a result of the metabolic metals as a result of the metabolic activity of microorganisms.There activity of microorganisms.There are about a dozen of bacteria are about a dozen of bacteria known to cause microbial corrosion known to cause microbial corrosion of carbon steels, stainless steels, of carbon steels, stainless steels, aluminum alloys and copper alloys aluminum alloys and copper alloys in waters and soils with pH 4~9 and in waters and soils with pH 4~9 and temperature 10temperature 10ooC~50C~50ooC. These C. These bacteria can be broadly classified bacteria can be broadly classified as aerobic & anaerobic. Sulphate as aerobic & anaerobic. Sulphate reducing bacteria (SRB) is reducing bacteria (SRB) is anaerobic and is responsible for anaerobic and is responsible for most instances of accelerated most instances of accelerated corrosion damages to ships and corrosion damages to ships and offshore steel structures. Iron and offshore steel structures. Iron and manganese oxidizing bacteria are manganese oxidizing bacteria are aerobic and are frequently aerobic and are frequently associated with accelerated pitting associated with accelerated pitting attacks on stainless steels at welds.attacks on stainless steels at welds.

EFFECTS OF CORROSION:-EFFECTS OF CORROSION:-

The consequences of corrosion are many and varied The consequences of corrosion are many and varied and the effects of these on the safe, reliable and and the effects of these on the safe, reliable and efficient operation of equipment or structures are efficient operation of equipment or structures are often more serious than the simple loss of a mass of often more serious than the simple loss of a mass of metal.  Failures of various kinds and the need for metal.  Failures of various kinds and the need for expensive replacements may occur even though the expensive replacements may occur even though the amount of metal destroyed is quite small.  amount of metal destroyed is quite small. 

• Reduced Strength• Downtime of equipment• Escape of fluids• Lost surface properties• Reduced value of goods• Economic losses

CORROSION PREVENTION:-CORROSION PREVENTION:-Electrically insulate the two metals from each other. Unless they are Electrically insulate the two metals from each other. Unless they are in electrical contact, there can be no galvanic couple set up. in electrical contact, there can be no galvanic couple set up. Coating the two materials or if it is not possible to coat both, the Coating the two materials or if it is not possible to coat both, the coating shall be applied to the more noble, the material with higher coating shall be applied to the more noble, the material with higher potential. potential. Another way is to keep the metals dry and/or shielded from ionic Another way is to keep the metals dry and/or shielded from ionic compounds (salts, acids, bases), for example by painting or encasing compounds (salts, acids, bases), for example by painting or encasing the protected metal in plastic or epoxy, and allowing them to dry.the protected metal in plastic or epoxy, and allowing them to dry.Proper selection of materials with known resistance to the service Proper selection of materials with known resistance to the service environment .environment .Control pH, chloride concentration and temperature Control pH, chloride concentration and temperature Cathodic protection and/or Anodic Protection.Cathodic protection and/or Anodic Protection.Regular mechanical cleaning if possible. Regular mechanical cleaning if possible. Chemical treatment with biocides to control the population of bacteria. Chemical treatment with biocides to control the population of bacteria. Complete drainage and dry-storage.Complete drainage and dry-storage.

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