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1. Chemical degradation of
materials

2. RUBBERS
• Rubbers and elastomers have good resilience
property, because of their flexibility they are used in
applications like tubing, belting and automobile
tires.
• Chemical and abrasion resistance, good insulating
qualities result in corrosion resistance.
• Natural rubbers have better mechanical properties
and synthetic rubbers have better corrosion
resistance.

3. Natural Rubber
• Rubber is a long chain molecule of isoprene.
• It comes from the trees as a liquid latex.
• The coil like structure is responsible for the high
elasticity.
• Soft rubber has a temperature limitation of around
16F
• By hardening through alloying with sulphur this
temperature can be raised to 180F. It makes the
rubber harder and brittle.
• This process is called vulcanization and discovered by
Charles Goodyear in 1839.
• Adding this sulphur results in a hard product known as
ebonite, used for make of bowling balls.

4. • Semi hard and hard rubber are used for
tires, tank linings and other items.
• Corrosion resistance increases with
hardness.
• In the case of pipes and tanks the
rubber is soft and cured in place or in
autoclaves.
• Modulus of elasticity varies from 500 to
500000lb/in2.

5. Synthetic Rubbers
• At the start of world war II sources of rubber was
taken away by enemy so substitutes of rubber were
made.
• Neoprene was developed in early 30’s by Du Pont in
1941.
• A wide variety of synthetic rubber is used with a
combination of plastic.

6. • -Neoprene and nitrile rubber possess resistance to
oils and gasoline.
• One of the primary applications of neoprene is
gasoline hoses.
• It is also used as a inner tube and process
equipment such as a seal for floating top storage
tanks.
• Neoprene lined vessels also resist strong NaOH.
• -Butyl rubber gives better oxidising resistance to
oxidising environment such as air and dil. HNO3.

7. • Rubbers are compounded to produce a wide range
of mechanical properties.
• Hardness varies from bone hard to soft.
• Tensile strengths vary from 900 to 4500 psi,
• Elongation varies form 0 to 1000%
• Soft rubbers are best for abrasion resistance.
• Hard rubbers should not be used for erosion
corrosion applications.

8. Elastomers and their properties
ELASTOMER NAME TRADE
NAME
PROPERTIES
1. Cholorosulphanated
polyethylene
Hypalon Resembles neoprene with greater resistance to
heat, ozone, chemicals
2. Ethylene propylene Nordel Similar to butyl rubber with additional advantage
of excellent resistance to ozone, heat, water,
sunlight.
3. Epichlorhydrin Hydrin Good properties of neoprene and nitrile rubbers,
excellent resistance to swelling in fuels and oils,
good heat aging properties.
4. Fluorelastomers Viton Has excellent resistance to variety of corrosives
and hydrocarbons and resistance to ozone, heat,
water, sunlight.
5. Urethane Adiprene Good tensile strength , wear resistance and good
resistance to oils, ozone, oxidation

9. Plastics
• Plastics are now available in various forms, and
they are produced by casting, molding, extrusion
and calendering.
• They are available as solid parts, linings, coatings,
foams, fibers, films.
• Plastic is a material that contains an organic
substance as the essential element of large
molecular weight, in solid finished state and at
some stage in its manufacture or in its processing
finished articles.

10. • Plastics are compared with metals and alloys as
much weaker, softer, more resistant to chloride ions,
HCL, less resistant to conc H2SO4 and oxidising
environment.
• Cold flow or creep at ambient temperature is a
problem with thermoplatics.
• Plastics are of 2 types:
• Thermoplastics- former soften with increase in
temperature and return to the original hardness
when cooled. eg.nylon.
• Thermosetters- harden when heated and retain
hardness when cooled, they set into permanent
shape on heat under pressure.
• Plastics do not dissolve like metals they degrade or
swell and loss mechanical properties, softening,
hardening and spalling.

11. • THERMOPLASTICS:
NAME OF
THERMOPLASTIC
KNOWN
AS
PROPERTIES APPLICATIONS
Fluorocarbons
Polytetrafluorethylene
Teflon
TFE
Corrosion resistant to
all environments upto
550F. Contains C and F.
Low coefficient of
friction
Used as sleeve to separate plug
and body of plug valve, acts as
lubricant of metal parts. other
uses are pipe, tape, valve
diaphragms, coatings, insulator
Methyl methacrylate
(Lucite and Plexiglas)
Acrylics Pretty, transmits,
conducts light, soft,
easily scratched, not
very temp resistant
Use for brush, purse handles,
transparent displays, working
models, airplane canopies,
tailights.
Nylon Hosiery Strength, corrosion
resistant, wear
resistance
Gears, drawer, shelf rollers,
fishline, brush bristles.
Chlorinated Polyether Penton Handles corrosives, Valve, pipe, linings and coatings.

12. NAME OF
THERMOPLASTIC
KNOWN
AS
PROPERTIES APPLICATIONS
Polyethylene
Alathon, aeroflux,
Polythene
Ultrahigh molecular
weight polyethylene
UHMWPE Good resistance to
erosion corrosion
Used for packaging film, sheet,
squeeze bottle, pans, tumblers
Used in valve, pump impellers
Polypropylene Moplen,
Pro-Fax,
Escon
Better heat and
corrosion resistant
Valves,bottles, pipe, fitting,
scooter parts.
Polystyrene Styron,
lustrex
Good chemical
resistance, but
brittle
Wall tile, battery case, flowmeter,
radio cabinet, refrigerator
equipment
Rigid Polyvinyl chloride
(PVC)
PVC Rigid, on addition of
polyvinyl acetate
and plasticisers to
vary mechanical
properties
Pipe, fittings, ducts, fans, sheet,
containers, linings
Vinyl Tygon,
vinylite,
Plioflex,
saran
Pipe, tubing, packaging industry,
floor tile, raincoats, insulation

13. NAME OF
THERMOSETTER
KNOWN AS PROPERTIES APPLICATIONS
Epoxies Epon,
Duracon,
Araldite
Best corrosion resistance
and mechanical
properties, available as
castings, extrusions,
sheet etc
Used as sinks, bench tops, small
tanks, adhesives, pipe, valves,
dies
Phenolics Bakelite,
Durez,
Resinox
Telephone, electrical sockets,
radio cabinets, pumps, valves,
trays, rollers, coatings,
Polyesters Mylar,
dacron,
dypol,vibrin
Corrosion resistance is
more
Used in a satillite name space
mirror, body of an automobile
Silicones Dow
corning
Heat resistance Used in moulding compounds,
laminating resins, electronic
equipment
Ureas Lauxite,
Beetle,
avisco
Corrosion resistance not
that good
Used in kitchen dishware,
utensils, electrical fixtures.
• THERMOSETTERS:

14. NAME OF
THERMOSETTER
KNOWN
AS
PROPERTIES APPLICATIONS
Laminates and
Reinforced
Plastics
Fibre reinforce
plastic
Carbon FRP
FRP
Tensile strength is more
Erosion corrosion
allowance is good
HIGH STRENGTH
Pipe, ducts, sheets, car bodies,
boats, missiles
Used in pump
Structural applications of
automobiles and equipment

15. Ceramics
• Compounds of metallic and non
metallic element. MgO ,Brick, stone,
fused silica, glass, porcelain, cement,
abrasives, refractories.
• Better corrosion and abrasion
resistance, better insulators, brittle,
weaker in tension, subject to thermal
shock, good resistance to chemicals.

16. • Acid Brick:
• made from fireclay with a silica content > 10%
• Application: lining of tanks, other vessels to resist
the erosion corrosion resistance.
• Stoneware and Porcelain:
• Good corrosion resistance, good tensile strength
• Used in towers, pipe, valves, pumps, crocks,
adsorption towers.
• Structural Clay:
• Used in buildings, fire, sewer, paving brick,
roofing and wall tie.

17. • Glass:
• Amorphous inorganic oxide mostly silica cooled
to a rigid condition.
• Used in glass laboratory ware, pyrex.
• Vitreous silica:
• Called as fused quartz
• Better thermal properties, excellent corrosion
resistance
• Used in furnaces muffles, burners, absorbers,
reaction chambers,

18. • Concrete:
• Used for tanks and pipes for mild corrosives.
• In aggressive environment it is used with lining or
coatings.
• Others;
• Alumina: used in pump and valve seats, it has high
hardness, good wear, corrosion resistance.
• Silicon Carbide: performs well as spray nozzle for
Hot sulphuric acid

19. Carbon and graphite
• Good conductors of heat and electricity
• High thermal conductivity
• Excellent thermal shock resistance
• Used for heat exchangers, columns, pumps,
anodes
• Inert to corrosive environment
• Weak and brittle
• Abrasion resistance is poor.
• High temperature stability is good

20. • Carbon exhibits resistance to alkalies and acids
• Karbate is a resin bonded graphite used in
chemical process industries.
• Pyrolytic graphite it is dense, antistrophic
material, has better strength and oxidation
resistance

21. WOOD
• Cypress, pine, oak, redwood are the main woods
used for corrosion applications.
• Filter-press frames, structural members of
buildings, barrels, tanks are made of wood
• Wood is limited to water and dilute chemical
• Strong acids attack wood and also subject to
biological degradation
• Impregnation with wax and plastics help reduce
chemical and biological attack
• Wood is good for water cooling towers