Prevention of corrosion

A presentation covering the various methods of prevention of corrosion. Material selection, design of structures, alteration of materials, alteration of environment, cathodic & anodic protection, and coatings are the different methods used. These are briefly described.

1. PREVENTION OF PREVENTION OF
CORROSIONCORROSION
Dr. T. K. G. NamboodhiriDr. T. K. G. Namboodhiri
[Retd. Professor., Inst. Techno. , Banaras Hindu University][Retd. Professor., Inst. Techno. , Banaras Hindu University]
Consultant-Metallurgy & Corrosion,Consultant-Metallurgy & Corrosion,
Tiruvalla, KeralaTiruvalla, Kerala

2. PREVENTION OF PREVENTION OF
CORROSIONCORROSION
The huge annual loss due to corrosion is a The huge annual loss due to corrosion is a
national waste and should be minimizednational waste and should be minimized
Materials already exist which, if properly Materials already exist which, if properly
used, can eliminate 80 % of corrosion lossused, can eliminate 80 % of corrosion loss
Proper understanding of the basics of Proper understanding of the basics of
corrosion and incorporation in the initial corrosion and incorporation in the initial
design of metallic structures is essentialdesign of metallic structures is essential

3. METHODSMETHODS
Material selectionMaterial selection
Improvements in materialImprovements in material
Design of structuresDesign of structures
Alteration of environmentAlteration of environment
Cathodic & Anodic protectionCathodic & Anodic protection
CoatingsCoatings

4. MATERIAL SELECTIONMATERIAL SELECTION
Most important method – select the appropriate Most important method – select the appropriate
metal or alloy .metal or alloy .
““Natural” metal-corrosive combinations likeNatural” metal-corrosive combinations like
c.c. S. S.- Nitric acid, S. S.- Nitric acid,
d.d.Ni & Ni alloys- Caustic Ni & Ni alloys- Caustic
e.e.Monel- HF, Hastelloys- Hot HClMonel- HF, Hastelloys- Hot HCl
f.f.Pb- Dil. Sulphuric acid, Pb- Dil. Sulphuric acid,
g.g.Sn- Distilled water Sn- Distilled water
h.h.Al- Atmosphere, Al- Atmosphere,
i.i.Ti- hot oxidizers Ti- hot oxidizers
j.j.Ta- Ultimate resistanceTa- Ultimate resistance
Corrosion Tables available for various materials Corrosion Tables available for various materials
in different corrosive environmentsin different corrosive environments

5. IMPROVEMENTS OF IMPROVEMENTS OF
MATERIALSMATERIALS
Purification of metals- Al , ZrPurification of metals- Al , Zr
Alloying with metals for:Alloying with metals for:
c)c)Making more noble, e.g. Pt in TiMaking more noble, e.g. Pt in Ti
d)d)Passivating, e.g. Cr in steel Passivating, e.g. Cr in steel
e)e)Inhibiting, e.g. As & Sb in brassInhibiting, e.g. As & Sb in brass
f)f)Scavenging, e.g. Ti & Nb in S.SScavenging, e.g. Ti & Nb in S.S
Improving other propertiesImproving other properties
h)h)Change of microstructure. e.g. desensitization of s. s. Change of microstructure. e.g. desensitization of s. s.
welds.- prevents I.g. corrosionwelds.- prevents I.g. corrosion
i)i)Elimination of tensile stress-improves SCCElimination of tensile stress-improves SCC
j)j)Introduction of surface compressive stress-improves Introduction of surface compressive stress-improves
corrosion fatigue and SCC.corrosion fatigue and SCC.

6. DESIGN OF STRUCTURESDESIGN OF STRUCTURES
Avoid sharp cornersAvoid sharp corners
Complete draining of vesselsComplete draining of vessels
No water retentionNo water retention
Avoid sudden changes in sectionAvoid sudden changes in section
Avoid contact between dissimilar metalsAvoid contact between dissimilar metals
Weld rather than rivetWeld rather than rivet
Easy replacement of vulnerable partsEasy replacement of vulnerable parts
Avoid excessive mechanical stressAvoid excessive mechanical stress

7. ALTERATION OF ALTERATION OF
ENVIRONMENTENVIRONMENT
Lower temperature and velocityLower temperature and velocity
Remove oxygen/oxidizersRemove oxygen/oxidizers
Change concentrationChange concentration
Add InhibitorsAdd Inhibitors
Adsorption type, e.g. Organic amines, azolesAdsorption type, e.g. Organic amines, azoles
H evolution poisons, e.g. As & SbH evolution poisons, e.g. As & Sb
Scavengers, e.g. Sodium sulfite & hydrazineScavengers, e.g. Sodium sulfite & hydrazine
Oxidizers, e.g. Chromates, nitrates, ferric saltsOxidizers, e.g. Chromates, nitrates, ferric salts

8. CATHODIC & ANODIC CATHODIC & ANODIC
PROTECTIONPROTECTION
Cathodic protection: Make the structure Cathodic protection: Make the structure
more cathodic bymore cathodic by
–Use of sacrificial anodesUse of sacrificial anodes
–Impressed currentsImpressed currents
Used extensively to protect marine Used extensively to protect marine
structures, underground pipelines, water structures, underground pipelines, water
heaters and reinforcement bars in concreteheaters and reinforcement bars in concrete
Anodic protection: Make Passivating metal Anodic protection: Make Passivating metal
structures more anodic by impressed structures more anodic by impressed
potential. e.g. 316 s.s. pipe in sulfuric acid potential. e.g. 316 s.s. pipe in sulfuric acid
plantsplants

9. COATINGSCOATINGS
Most popular method of corrosion protectionMost popular method of corrosion protection
Coatings are of various types:Coatings are of various types:
–MetallicMetallic
–Inorganic like glass, porcelain and concreteInorganic like glass, porcelain and concrete
–Organic, paints, varnishes and lacquersOrganic, paints, varnishes and lacquers
Many methods of coating:Many methods of coating:
–ElectrodepositionElectrodeposition
–Flame sprayingFlame spraying
–CladdingCladding
–Hot dippingHot dipping
–DiffusionDiffusion
–Vapour depositionVapour deposition
–Ion implantationIon implantation
–Laser glazingLaser glazing

10. CONCLUSIONSCONCLUSIONS
Many methods are available to Many methods are available to
prevent/mitigate corrosionprevent/mitigate corrosion
One or a number of methods may be One or a number of methods may be
used simultaneously for effective used simultaneously for effective
protectionprotection
Proper selection of methods is Proper selection of methods is
essential for optimizing cost.essential for optimizing cost.