Materials of pharmaceutical plant construction
Contents of
this session
Factors affecting selection of plant material
Physical, chemical and economic factors
Classification of materials
Metals and non-metal materials
Non Ferrous metals
Thermosetting Plastic
Polystyrene
Learning
objectives
Enlist the factors affecting selection of plant material
Understand the physical, chemical and economic factors
Classify materials
Discuss the metal and non-metal materials
Enlist the non-ferrous materials
Discuss non-metals used for plant construction
Discuss thermoplastics
Factors
affecting selection of material for pharmaceutical plant construction
The success or failure of s new chemical plant or in the
improvement of an existing facility depends on
1. Design of equipment-easy to clean,
install, operate
2. Selection of material-Physical,
chemical, Economical
Physical
·
Strength: to withstand the stress and and
rigours
·
Mass: to transport
·
Wear and tear: to mill and grind
·
Thermal conductivity: evaporators, dryers
·
Thermal Expansion: material should maintain
size, should not expand.
·
Cleansing: Smooth and polished surfaces
·
Sterilization: Material should withstand the
heat and pressure.
·
Transparency: permits the visual observation of
reactions and processes.
Chemical
Contamination: Substance’s such as
glass, silica, lead, cast iron, steel, tinned iron and variety of alloys are
used in construction of pharma plant and most of them produce contamination.
Ex: Heavy metals inactivates penicillin, Appearance changes, may be toxic etc
Reactivity with chemicals: At
extreme pH, temperature and pressure, materials get corroded.
Economical
Cost of the material plays an
important role in the design of the plant.
Cost and utility of the material is
studied before making buying decision.
Classification of material
Metal
1. Ferrous
·
Cast Iron
·
Steel Carbon
·
Stainless steel
2. Non ferrous
·
Aluminium
·
Nickel
·
Lead
Non metal
1. Inorganic
·
Glass
·
Asbestos
2. Organic
·
Rubber
·
Timber
FERROUS METALS
Iron metal is one of the used
materials for the construction of plants because of its mechanical strength,
abundent availability and lower cost.
Some varieties of iron are discussed.
1. Cast iron:
It consists of iron with a
proportion of carbon (>15 %). The properties of iron depend on the amount of
iron present in it.
Cast iron is abundently available,
inexpensive and therefore widely used. A number of types of cast iron are
available.
Advantages:
Cast iron is cheap. Therefore, it
is used in place of expensive plant material for coating
Since cast iron has low thermal
conductivity, it is used for the construction of outer surface of jackets of
steam pans.
Low melting temperatures 1140/1200*C
Disadvantages:
Cast iron is very hard and brittle.
Therfore, it is difficult to machine. This disadvantage can be overcome by the
addition of different materials to improve his performance.
Cast iron is attacked by dil.H2SO4,
dil. Nitric acid and dilute as well as con HCl.
It is resistant to conc. H2SO4,
nitric acid and alkalis.
Since cast iron has low thermal
conductivity, it cannot be used for heat transfer in steels.
Uses:
It is commonly used for the
construction of:
·
Supports for plant
·
Jackets of steam pans
·
Linings with enamel, plastic or suitable
protective material.
Modification of cast iron: Cast
iron is not considered corrosion resistant. The characteristics of cast iron
can be altered by alloying with other elements such as silicon, nickel and
chromium
Commercial types: duriron and
durichlor.
2. Carbon steel
Carbon steel is an iron alloy,
which contains only a small % of carbon.
Advantages:
Carbon steel is cheapest.
Therefore, it is preferred.
It is easily weldable and is
freqently used in fabrication
Disadvantages:
Carbon steel has limited resistance to corrosion. This property can be
improved by preparing alloys.
It reacts with caustic soda, brine
and sea water. Alloying it can reduce this reactivity.
Uses:
Carbon steel is used for the
construction of bars, pipes and plates. It is used to fabricate large storage
tanks for water, sulphuric acid, organic
solvents etc.
It is used for supporting
structures such as grinders and bases for plant vessels.
VARIENTS OF CARBON STEEL:
The properties of carbon steel can
be altered by alloying it with other metals.
Some of the metals and their properties are:
Nickel (Ni) – improves toughness,
corrosion resistance and low temperature properties.
Chromium (Cr)/ increase hardness,
more abrasive resistant and resistance to oxidation.
Silicon (Si)/ increase hardness,
more abrasive resistant and resistance to oxidation.
Molybdenum (Mb)/ provides strength
at elevated temperatures.
3. Stainless steel
It is an alloy of iron. Usually, it
contains chromium and nickel, which make the steel corrosion resistant.
Stainless steel is stabilized by
the addition of titanium, niobium, and
tantalum. Minor amount of other elements such
as copper, molybdenum selenium are added. Stainless
and steel also has the advantage of ease in fabrication.
The abundant use of stainless steel
is due to the properties such as
Heat resistance
Corrosion Resistance
Ease of fabrication
Cleaning and sterilization
Tensile strength
Depending on the composition,
stainless steel alloys are available in 3 groups viz., martensitic, ferritic
and austenitic.
Alloys of stainless steel (SS): are
allowed with other metal so an to modify its properties. The metals
incorporated into SS are,
Titanium (Ti)
Niobium (Nb)
Tantalum (Ta)
Chromium (Cr)
Carbon (C)
Silicon (Si)
Nickel (Ni)
Manganese (Mn)
Copper (Cu)
Non Ferrous metals
Aluminium
Lead
Copper
Nickel
Chromium
Silver
Platinum
ALUMINIUM
A number of aluminium items are
used in regular day to day life.
Aluminium is cheap, light in weight and offers adequate mechanical
strength. In addition, aluminium equipment can be easily fabricated. Further,
aluminium can be strengthened by cold working. Their maintenance and cleaning
is also easy. Hence, its utility is
mostly recommended. However the use of aluminium in the construction of plant
and equipment is limited.
Advantages:
High resistance to atmospheric
conditions, industrial fumes, vapour and fresh or salt waters. Aluminium can be
used with conc. Nitric acid (above 82%) and acetic acid.
Thermal conductivity of aluminium
is 60% that of pure copper.
Disadvantages:
The mechanical strength decreases
greatly above 150*C.
aluminium cannot be used with
strong caustic solution.
Many mineral acids attack aluminium.
Oxide and hydro/ oxide films are
formed rapidly, when its surface is exposed. Normally this film is thickened by
chemical and electrolytic means. This provides so called anodised finishes.
SILVER
Because of its high cost, silver is
used only as a material of plant construction in special cases and usually
silver coated material is used rather than solid silver.
It is not resistant to concentrated
HCl or H2SO4, any strength of nitric acid, and sulphur and sulphur compounds.
It is resistant to organic acids
and their salts. It is even more malleable and ductile than copper and,
therefore, capable of being readily worked. It has a higher thermal
conductivity than all other metals.
A few e.g. of its special uses are
– plant for the manufacture of salicylates and acetic acid; a silver/ plated
basket for a hydroextracter used in vitamin crystallisation; a solid silver
vessel in a cast/ iron jacket for bromination.
TITANIUM
Titanium has become increasingly
important as a construction material. It
is strong and of medium weight.
Titanium is usually not bothered by
impingement attack, crevice corrosion, and pitting attack in seawater. Its
general resistance to seawater is excellent.
Titanium is not easy to form, it
has a high spring back
NICKEL
Nickel is resistant to oxidation
and alkalis but is attacked slowly by dilute mineral acids and rapidly by
concentrated acids.
It is resistant to the weak organic
acids occuring in pharmaceutical preparations, e.g. citiric, tartaric and
stearic.
It is also resistant to phenols.
Its salts are non oxic. It is useful for such plant as pans, vats, tanks,
mixers, valves, and pumps, nickel wire may be woven to form filter cloths.
CHROMIUM
Although Hard and resistant to
corrosion, chromium is not normally used as material of plant construction.
It forms resistant alloy with
nickel and, probably, its most important use is in the manufacture of stainless
steel.
It is also, of course, used as a
plating to protect steel.
Non Metals
Glass
Rubber
Plastic
·
Thermosetting Plastic
·
Thermoplastic
General properties
Resistant to chemicals
Resistant to contamination
Corrosion resistant
Easy to fabricate
Application
Flooring
Roofing
Windows & doors
Piping
Storage tanks
Insulation materials
Thermosetting Plastic
Permanently shaped to rigid
structure during manufacturing.
·
Phenol formaldehyde
·
Bakelite (cookwear handle)
·
Melamine (iron)
Thermoplastic
Soften under the influence of heat
·
Poly vinyl Chloride (PVC)
·
Polyethylene/Polypropylene
·
Polystyrene
·
Acrylonitrile Butadiene Styrene (ABS)
·
Cellulose Acetate Butyrate (CAB)
Poor resistance to organics
Polyvinyl chloride
Clear, tough, inert
Stabilizer or colorant can be
incorporated
Resistant to acids
Resistant to alkali
Crack readily (plasticizer added to
reduce this)
Turn yellow when exposed to UV
Polyethylene
Economical
Density (0.91-0.96) determine
stiffness, transluscency, vapour transmission
More density-> more stiffness,
less permiable, less, resistant to cracking
Pipe of Polyethylene must be fully
supported
Stable upto 1200F
Polyporopylene
Good resistance to chemical, acids,
alkali
Tough and flexible
Resistance to fatigue (weakening of
a material caused by repeatedly applied loads)
Stable upto 2500F
Brittle at low temperature, Used
for manufacturing piping systems
Polystyrene
High mechanical strength
Chemical resistant
Rigid
Clear
Easy to scratch
Brittle (rubber or acrylic
compounds can be mixed to improve properties)
Stable upto 1900F
Acrylonitrile Butadiene Styrene (ABS)
Acid resistant
Resistant to organic solvents
Not resistant to alkali
Summary
The success or failure of s new
chemical plant or in the improvement of an existing facility depends on:
1. Design
of equipment
2. Selection
of material
Alloys of stainless steel (SS): are
allowed with other metal so an to modify its properties.
A number of aluminium items are
used in regular day to day life.
Aluminium is cheap, light in weight and offers adequate mechanical
strength. In addition, aluminium equipment can be easily fabricated.
Although Hard and resistant to
corrosion, chromium is not normally used as material of plant construction. It
forms resistant alloy with nickel and, probably, its most important use is in
the manufacture of stainless steel.
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