TYPE 1UNIFORM CORROSION1. General corrosion produced by most direct chemical attacks2. Common form of corrosion3. First seen as a general dulling of the surface and if allowed to continue the surface becomes rough4. Prevention: use thicker materials for CA, paints or metallic coatings such as plating, galvanizing or

anodizing, use corrosion inhibitors or modifying the environment

TYPE 2GALVANIC CORROSION1. Dissimilar metal corrosion – takes place when two metals are in physical contact with each other

and are immersed in a conducting fluid (2 dissimilar materials are coupled in a corrosive electrolyte)2. E.g Plate and screw of different electrical potentials due to differences in processing

TYPE 3DIFFERETIAL AERATION CORROSION1. This corrosion takes place when a metal is unevenly exposed to different O2/ air concentrations2. The part exposed to less O2 undergoes corrosion

3. E.g drop corrosion takes place when a drop in electrolyte is in contact with the metal surface. The metal surface covered by is in contact with lesser amount of air than the uncovered metal surface. Thus, meta lcovered drop becomes anodic and corroded

TYPE 4PITTING1. Is a localized form of corrosive attack that produces holes or small pits in a metal. The bulk of

surface remains unattacked. 2. Often found in situations where resistance against general corrosion is conferred by passive surface

films. 3. Localized pitting attack is found where these passive films have broken down.4. Pitting attack induced by microbial activity such as sulfate reducing bacteria also deserves special

mention.

TYPE 5STRESS CORROSION1. Is observed in fabricated articles which are subject to various mechanical operations (such as

bending, hammering and annealing).

TYPE 6CORROSION FATIGUE1. Caused by the combined effects of cyclic stress and corrosion

TYPE 7CREVICE CORROSION1. Localised form of corrosion associated with a stagnant solution on the micro environmental level2. Such stagnant microenvironments tend to occur in crevices (shielded areas) such as those formed

under gaskets, washers, insulation material, fastener heads, surface deposits, disbanded coatings, threads, lap joints and clamps.

TYPE 8INTERGRANULAR CORROSION1. Refers to preferential (localized) corrosion along grain boundaries (or adjacent to grain boundaries)

while the bulk of the grains remain largely unaffected.2. Associated with chemical segregation effects or specific phases precipitated on the grain

boundaries. 3. Intergranular corrosion in sensitized stainless steels and exfoliation in aluminum alloys represent

industrially significant examples of this form of damage.

TYPE 9MICROBIOLOGICAL CORROSION1. Caused by microbes like bacteria, algae fungi etc2. The main product of corrosion in anaerobic corrosion is iron sulphide.

TYPE 10FILIFORM CORROSION1. Occurs under painted or plated surfaces when moisture permeates the coating. 2. Can be visually recognized without using a microscopy.3. Prevented via controlling the relative humidity and use brittle coatings.

TYPE 11EROSION CORROSION1. Is the result of relative movement between the corrosive fluid and metal surface2. All types of equipment exposed to moving fluids are subjected to erosion corrosion.

TYPE 12SOIL CORROSION1. Factors: moisture and dissolved electrolytes present in soil2. Presence of micro-organism in soil further leads to corrosion of underground and pipeline

TYPE 13HYDROGEN DAMAGE1. High strength steel become brittle and fracture following exposure to hydrogen2. Can be divided into hydrogen blistering, hydrogen embrittlement, decarburization and hydrogen

attack.