Corrosion types that can be prevented with proper care

Corrosion in Cement Atmospheric Corrosion
» Porousity remaining after cement solidification
» Alakline/Neutral nature of Cement
» Atmospheric humidity changes to acidic nature
    forming Carboxylic Acid
» Bonding strength is reduced
» Corrosion Intensity varies on the type of steel used
» Temperature changes weakens the cement bonding
» Humidity forms Corboxylic Acid

Pitting Corrosion Stress Corrosion
» Chemical breakdown of passivity of a substance
    – creation of holes in metal
» Corroding substance starts taking the skin of
    the metal at localized points
» Depends on environmental factors such as chloride,
    oxygen, pH, conductivity, temperature etc.
» Tensile stress (stretching) on a metal surface results
    in the exposure of the metal to the atmospheric
    condition.
» This is an extension of pitting corrosion

Crevice Corrosion Galvanic Corrosion
Takes place in shielded metal surface area
» Interfacing of pipe couplings
» Threaded or riveted connections
» Gasket fittings
» Spot welded lap joints
» Porous welds
» Coiled or stacked sheets of metal
» When totally dissimilar metals remain in contact in
    a particular atmospheric condition then it leads
    to galvanic corrosion.
» Prevention: Bone Plate and Bone Screws. These should
    be made with the same metal to avoid any Galvanic
    corrosion. Use Brass screws in Brassware

Inter Granular Corrosion Erosion Corrosion
When metals are subjected to super heat conditions like 950°F to 1450°F, the grain structure of the steel changes and phenomena of precipitation of metallic compounds of the grain bonding is observed at the corner of the metal.
When liquid, gas or water flows on metal and the metal is corroded, this type of corrosion takes place, due to the pH of water and the velocity

Corrosion causes / factors Corrosion damages
» Atmospheric Temperature Change
» Humidity - Hydrogen and Oxygen in atmosphere
» Oxidation with polluted air - Carbon
» Acidic conditions in atmosphere
» Conversion of pH from Alkaline to Acidic Nature
» Metallic surfaces - mild sheets (MS)
» Pipes and GI Pipes
» Iron Frames and Grills
» Lower Surface of Vehicles
» Ships and Boats
» Bridges and Marine equipments
» Plastered Cemented Walls (RCC)

 

Epoxy versus PU System
# Attributes Epoxy Topcoat PU (2 Pack)
1 Material Type Resinous two pack system with Zinc Phosphate / Chromate anticorrosive Single / Two pack Intrinsic High-polymer
2 Technology Old and getting obsolete Latest Two pack polymer technology with inherited anticorrosive
3 Elasiticity Poor Excellent
4 Chemical Resistance Good Excellent
5 Alkali Resistance Good Excellent
6 Toxicity Contains no toxic material Non Toxic
7 Sun Light Exposure Unaffected Unaffected
8 Weather Resistance Good Excellent
9 Effect of Ageing Becomes hard and brittle Completely Flexible (Aliphatic System)
10 Heat Tolerance Temperature Up to 120oC Up to 250oC
11 Flammability Non-Flammable Flammable in uncured condition
12 Burning Rate Slow Slow
12 Passage of Light Semi-opaque Semi-transparent
13 Colour Option Various Various
14 Colour Options Various Various
15 Tensile Strength Poor Very High
16 Thermal Insulation Poor Very Good
17 Water Resistance Poor Excellent
18 Water Resistance Poor Excellent
19 Typical coverage per litre for single coat 70 - 80 sq ft 1. 80 - 90 sq ft on Rough Surface
2. 150-300 sq ft on Wood, Metal & Smooth Surface.
20 Thinning Material Costly Epoxy Thinner MTO or Neptha
21 Pot-life (Ready to apply condition) Only 90 to 110 minutes single pack - 90 to 110 minutes
2 Pack - 40 to 45 minutes
22 Shelf Life 12 Months 24 Months
23 Depth per coat 35 to 40 Micron 30 to 55 micron in single pack
up to 100 micron in two pack system

« Paints
Cement / Concrete Corrosion

 

Vivid Rising water seepage protection

 

Corrosion in Cement
» Porousity remaining after cement solidification
» Alakline/Neutral nature of Cement
» Atmospheric humidity changes to acidic nature forming Carboxylic Acid
» Bonding strength in plaster material is reduced

 

Annual Corrosion Losses in Rs Crores
Annual Corrosion Losses

 

Methods to prevent Corrosion
» Use better grade Steel and Metal Sheets
» Improving the quality of base metal by alloying
» Surface preparation
» Apply coatings before installation
» Coating with non reactive metals like Zn & Al
» Cladding by welding
» Polymeric surface coatings

 

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