Page 171 - CW E-Magazine (2-4-2024)

Special Report

bond once the substrate is less by preventing condensation and the important being lining vessels. These
porous than the liner, or from a corro- absorption of fluids. This reduces the are sheet-applied to a steel substrate,
sion/reaction product if the substrate speed and magnitude of temperature and are used extensively as membranes
is attacked by the permeative; and changes, keeping blisters to a minimum. in acid-brick lined vessels to safeguard
Loss of contents through the sub- The use of operative procedures or the steel shell from corrosive attack.
strate and liner as a result of the ulti- devices that limit the ratio of process In contrast to metals, elastomers
mate failure of the substrate. (In un- pressure reductions or temperature can absorb varied quantities of the substances
bounded linings, it is vital that the provide additional protection. that they come into contact with, parti-
house between the liner as well as cularly organic liquids. This may end
the support member be vented to the One of the applications for plastic in swelling, cracking and penetration
atmosphere to permit minute quanti- materials is to resist atmospheric cor- of the substrate in an elastomer-lined
ties of permeating vapours to flee rosion. By having the ability to resist vessel. Swelling will cause softening
and to stop the growth of entrapped attack by specific corrodents in plant of the stuff and, during a lined vessel,
air from collapsing the liner). The operations, they’re also able to resist introduce high stresses and failure of
fluoropolymers are significantly corrosive fumes in the atmosphere. the bond. Permeation is another issue
affected by permeation. Thermoplastic materials are joined that will cause lining failure. Once an
by either solvent cementing, thermal elastomer exhibits a high absorption,
The thickness of a lining affects fusion or by means of adhesives. In permeation typically results.
the permeation rate. For general corro- general, the adhesives that are most
sion resistance, thicknesses of 0.010 to immune to high temperatures typically Permeation will create significant
0.020 inches are typically satisfactory. exhibit the simplest resistance to chemi- problems in elastomeric-lined instru-
The rate of permeation is affected by cals and solvents. mentation. Once the corrodent permea-
temperature and pressure, concentra- tes the elastomer, it comes into contact
tion of permeate; and thickness of the The thermosetting resins are high- with the metal substrate. This may
polymer. molecular-weight polymers that are result in:
strengthened with glass or different Bond failure and blistering, caused

The density of the polymer can have suitable materials to produce mechani- by an accumulation of fluids at the
an impact on the permeation rate. The cal strength. The most commonly used bond;
thickness can usually decrease perme- resins are the vinyl esters, epoxies, Failure of the substrate attributable

ation by the square of the thickness. polyesters and furans. For reinforcing to corrosive attack; and
The densee the sheet, the lower will be these polymers, fibrous glass of F and Loss of contents through the lining

the permeation rate. The rate of perme- C grades is most ordinarily used. and substrate because of the failure
ation is also affected by the temperature of the substrate.
and gradient within the lining. Lower- Chemical corrosion takes place
ing these can cut back the speed of once the bonds within the thermoset are Although elastomers may be bro-
permeation. Lined vessels like storage broken by means of a chemical process ken by mechanical means, this isn’t
tanks, which are used in closed condi- with the polymer’s surroundings. It typically the case. Most mechanical
tions, give the most effective service. is sometimes irreversible. As a result harm happens as a result of chemical
of chemical corrosion, the compound deterioration. Once the elastomer has
Polymers have the potential to soak itself is also affected. For instance, the deteriorated somewhat, the material
up varied amounts of corrodents, espe- compound is also embrittled, softened, is weakened and becomes more prone
cially organic liquids. This will end in charred, crazed, delaminated, discolou- to mechanical harm from flowing or
swelling, cracking and penetration of red, dissolved, blistered or swollen. agitated media. Some elastomeric
the substrate of a lined part. Swelling Curing the resin plays a very impor- materials are subject to degradation
will cause softening of the polymer, tant role in the chemical resistance of once placed in outdoor applications as
introduce high stresses and cause failure the thermosetting. Improper activity a result of weathering. The action of
of the bond on lined elements. If the can lead to a loss of corrosion-resistant daylight, ozone and chemical elements
polymer has a high absorption rate, properties. will cause surface cracking, discolora-
permeation is likely to happen. Thermal tion of coloured stocks, serious loss
insulation of the substrate can cut back Elastomeric materials have a large of strength, elongation and alterna-
the gradient across the vessel, there- range of applications, one of the most tive rubber-like properties. Therefore,

Chemical Weekly April 2, 2024 171

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