Page 171 - CW E-Magazine (20-5-2025)

Special Report

Common insulation materials & insulation for preventing

corrosion under insulation

IntroductIon Noise reduction Dr. S.K. ChaKravorty
n many industrial processes, the Fire protection Consultant (Plant Engineering)

ability to regulate the temperature
Iin process vessels, tanks, steam These reasons determine the choice Email: chakravorty4410@gmail.com
boilers, waste heat recovery boilers, of insulation material, and the type of ditions. Conduction across a composite
chemical reactors, autoclaves and cladding/jacketing used. There are vari- wall occurs when heat flows from one
other equipment is a critical factor. The ous insulation standards and guidelines side of the wall to the other through
petrochemical, food, pharmaceutical around the world. The CINI Industrial multiple layers of different materials.
and specialty chemical sectors are just Insulation Manual may be used as a The heat transfer rate through a com-
some of the industries that depend on guideline for thermal insulation. posite wall depends on the thermal con-
temperature regulation. Uncontrolled ductivity, thickness, and surface area of
and unwanted loss of energy generally When going through the above each layer, as well as the temperature
translates to process and cost inefficien- reasons for insulation, we see that only difference across the wall.
cies. For example, in the oil and gas insulation for personnel protection
industry, the evaporation of crude oil could perhaps be considered for removal The overall heat transfer rate through
can lead to a loss of hydrocarbon pro- and replacement with something like a composite wall can be determined by
duct and environmental pollution due protective guards. However, because applying the principles of thermal resis-
to the release of volatile organic com- environmental and energy-saving goals tance. Each layer of the wall offers a
pounds (VOCs). have become more important in recent certain amount of thermal resistance to
years, the removal of insulation even heat flow, and the overall thermal resis-
To resolve these issues, industrial for this reason should be critically tance of the composite wall is the sum
plants have traditionally used thermal assessed. of the thermal resistances of each layer.
insulation to help maintain the desired This can be expressed mathematically
temperature within a storage, process When considering heat transfer using the equation: R Total = R1 + R2 +
or transportation vessel. However, through a wall, the mode of transfer that R3 +... + Rn, where, R Total is the total
while conventional insulation is rela- dominates depends on the specific cir- thermal resistance of the composite/
tively efficient at temperature control, it cumstances. For example, in a furnace, insulated wall, and R1, R2, R3,…Rn
is also known to promote a severe type heat transfer through the furnace wall are the thermal resistances of each layer.
of corrosion known as corrosion under occurs primarily by conduction since
insulation (CUI)(1). the solid wall material is the primary The overall heat transfer rate, or
barrier between the high-temperature heat flux, can then be determined using
New insulating coatings are quickly furnace interior and the surrounding Fourier’s law of heat conduction, which
gaining popularity due to their ability to cooler environment. In a building, heat states that the heat flux is proportional
drastically reduce product vapour loss transfer through the walls can occur by to the temperature difference across
and volatile organic compounds, while all three modes, but conduction is typi- the wall and inversely proportional to
at the same time eliminating CUI. cally the most significant. The rate of the total thermal resistance of the wall.
heat transfer through a wall depends Heat transfer through a composite wall
reasons for insulation on the thermal conductivity of the wall can be optimized by selecting materials
The first question that always has to material, the thickness of the wall, the with high thermal conductivity for the
be answered is the reason for insulating, temperature difference across the wall, layers with the largest temperature dif-
which can be one or a combination of and the surface area of the wall. ference, and with low thermal conduc-
the following: tivity for the layers with the smallest
Heat conservation or energy saving An insulated metallic surface con- temperature difference. Additionally,
Process control sists of two or more layers of different the thickness and surface area of each
Freeze protection/winterization materials with varying thermal conduc- layer can be adjusted to maximize the
Personnel protection tivities, thicknesses, and boundary con- overall heat transfer rate.

Chemical Weekly May 20, 2025 171

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