INSULATION MATERIALS AND
PROPERTIES
2.1 DEFINITION OF
INSULATION
Insulations are defined as
those materials or combinations of materials which retard the flow of heat
energy by performing one or more of the following functions:
1. Conserve energy by
reducing heat loss or gain.
2. Control surface
temperatures for personnel protection and comfort.
3. Facilitate temperature
control of process.
4. Prevent vapour flow and
water condensation on cold surfaces.
5. Increase operating efficiency
of heating/ventilating/cooling, plumbing, steam, process and power systems
found in commercial and industrial installations.
6. Prevent or reduce
damage to equipment from exposure to fire or corrosive atmospheres.
7. Assist mechanical
systems in meeting criteria in food and cosmetic plants.
8. Reduce emissions of
pollutants to the atmosphere.
The temperature range,
within which the term "thermal insulation" will apply, is from -75°C
to 815°C. All applications below -75°C are termed "cryogenic", and those
above 815°C are termed "refractory".
Thermal insulation is
further divided into three general application temperature ranges as follows:
2.2 GENERIC TYPES AND
FORMS OF INSULATION
The type indicates
composition (i.e. glass, plastic) and internal structure (i.e. cellular,
fibrous). The form implies overall shape or application (i.e. board, blanket,
pipe covering).
2.2.1 TYPES
1. Fibrous Insulation -
composed of small diameter fibers which finely divide the air space. The fibers
may be perpendicular or parallel to the surface being insulated, and they may
or may not be bonded together. Silica, rock wool, slag wool and alumina silica
fibers are used. The most widely used insulations of this type are glass fiber
and mineral wool. Glass fiber and mineral wool products usually have their
fibers bonded together with organic binders that supply the limited structural
integrity of the products.
2. Cellular Insulation -
composed of small individual cells separated from each other. The cellular
material may be glass or foamed plastic such as polystyrene (closed cell),
polyisocyanurate and elastomeric.
3. Granular Insulation -
composed of small nodules which may contain voids or hollow spaces. It is not
considered a true cellular material since gas can be transferred between the
individual spaces. This type may be produced as a loose or pourable material,
or combined with a binder and fibers or undergo a chemical reaction to make a
rigid insulation. Examples of these insulations are calcium silicate, expanded
vermiculite, perlite, cellulose, diatomaceous earth and expanded polystyrene.
2.2.2 FORMS
Insulations are produced
in a variety of forms suitable for specific functions and applications. The
combined form and type of insulation determine its proper method of installation.
The forms most widely used are:
1. Rigid boards, blocks,
sheets, and pre-formed shapes such as pipe insulation, curved segments, lagging
etc. Cellular, granular, and fibrous insulations are produced in these forms.
2. Flexible sheets and
pre-formed shapes. Cellular and fibrous insulations are produced in these
forms.
3. Flexible blankets.
Fibrous insulations are produced in flexible blankets.
4. Cements (insulating and
finishing). Produced from fibrous and granular insulations and cement, they may
be of the hydraulic setting or air drying type.
5. Foams. Poured or froth
foam used to fill irregular areas and voids. Spray used for flat surfaces.
2.3 PROPERTIES OF
INSULATION
2.3.1 THERMAL PROPERTIES
OF INSULATION
Thermal properties are the
primary consideration in choosing insulations.
a. Temperature limits:
Upper and lower temperatures within which the material must retain all its
properties.
b. Thermal conductance
"C": The time rate of steady state heat flow through a unit area of a
material or construction induced by a unit temperature difference between the
body surfaces.
c. Thermal conductivity
"K": The time rate of steady state heat flow through a unit area of a
homogeneous material induced by a unit temperature gradient in a direction
perpendicular to that unit area.
d. Emissivity
"E": The emissivity of a material (usually written ε or e) is the
relative ability of its surface to emit energy by radiation. It is the ratio of
energy radiated by a particular material to energy radiated by a black body at
the same temperature.
e. Thermal resistance
"R": Resistance of a material to the flow of heat.
f. Thermal transmittance
"U": The overall conductance of heat flow through an
"assembly".
2.3.2 MECHANICAL AND
CHEMICAL PROPERTIES OF INSULATION
Properties other than
thermal must be considered when choosing materials for specific applications.
Among them are:
a. Alkalinity (pH) or
acidity: Significant when moisture is present. Also insulation must not
contribute to corrosion of the system.
b. Appearance: Important
in exposed areas and for coding purposes.
c. Breaking load: In some
installations the insulation material must "bridge" over a
discontinuity in its support. This factor is however most significant as a
measure of resistance to abuse during handling.
d. Capillarity: Must be
considered when material may be in contact with liquids.
e. Chemical reaction:
Potential fire hazards exist in areas where flammable chemicals are present.
Corrosion resistance must
also be considered.
f. Chemical resistance:
Significant when the atmosphere is salt or chemical laden and when pipe content
leaks.
g. Coefficient of
expansion and contraction: Enters into the design and spacing of
expansion/contraction joints and/or use of multiple layer insulation
applications.
h. Combustibility: One of
the measures of a material's contribution to a fire hazard.
i. Compressive strength:
Important if the insulation must support a load or withstand mechanical abuse
without crushing. If, however, cushioning or filling in space is needed as in
expansion/contraction joints, low compressive strength materials are specified.
j. Density: A material's
density may affect other properties of that material, such as compressive
strength. The weight of the insulated system must be known in order to design
the proper support.
k. Dimensional stability:
Significant when the material is exposed to temperature; expansion or shrinkage
of the insulation may occur resulting in stress cracking, voids, sagging or
slump.
l. Fire retardancy: Flame
spread and smoke developed ratings are of vital importance; referred to as
"surface burning characteristics".
m. Resistance to
ultraviolet light: Significant if application is outdoors and high intensity
indoors.
n. Resistance to fungal or
bacterial growth: Is important in all insulation applications.
o. Shrinkage: Significant
on applications involving cements and mastics.
p. Sound absorption
coefficient: Must be considered when sound attenuation is required, as it is in
radio stations, some hospital areas where decibel reduction is required.
q. Sound transmission loss
value: Significant when constructing a sound barrier.
r. Toxicity: Must be
considered in the selection of all insulating materials.
2.4 MAJOR INSULATION
MATERIALS
The following is a general
inventory of the characteristics and properties of major insulation materials
used in commercial and industrial installations.
2.4.1 CALCIUM SILICATE
Calcium silicate
insulation is composed principally of hydrous calcium silicate which usually
contains reinforcing fibers; it is available in molded and rigid forms. Service
temperature range covered is 35°C to 815°C. Flexural and compressive strength
is good. Calcium silicate is water absorbent. However, it can be dried out
without deterioration. The material is non-combustible and used primarily on
hot piping and surfaces. Jacketing is field applied.
2.4.2 MINERAL FIBER
a. Glass: Available as
flexible blanket, rigid board, pipe covering and other pre-molded shapes.
Service temperature range
is -40°C to 232°C. Fibrous glass is neutral; however, the binder may have a pH
factor. The product is non-combustible and has good sound absorption qualities.
b. Rock and Slag: Rock and
slag fibers are bonded together with a heat resistant binder to produce mineral
fiber or wool. Upper temperature limit can reach 1035°C. The same organic
binder used in the production of glass fiber products is also used in the
production of most mineral fiber products.
Mineral fiber products are
non-combustible and have excellent fire properties.
2.4.3 CELLULAR GLASS
Available in board and
block form capable of being fabricated into pipe covering and various shapes.
Service temperature range is -273C to 200°C and to 650°C in composite systems.
Good structural strength, poor impact resistance. Material is non-combustible,
non-absorptive and resistant to many chemicals.
2.4.4 EXPANDED SILICA, OR
PERLITE
Insulation material
composed of natural or expanded perlite ore to form a cellular structure;
material has a low shrinkage coefficient and is corrosion resistant;
non-combustible, it is used in high and intermediate temperature ranges.
Available in pre-formed sections and blocks.
2.4.5 ELASTOMERIC FOAM
Foamed resins combined
with elastomers to produce a flexible cellular material. Available in preformed
sections or sheets, Elastomeric insulation offer water and moisture resistance.
Upper temperature limit is 1050C. Product is resilient. Fire resistance should
be taken in consideration.
2.4.6 FOAMED PLASTIC
Insulations produced from
foaming plastic resins create predominately closed cellular rigid materials.
"K" values decline after initial use as the gas trapped within the
cellular structure is eventually replaced by air. Check manufacturers' data.
Foamed plastics are light weight with excellent cutting characteristics. The
chemical content varies with each manufacturer. Available in pre-formed shapes
and boards, foamed plastics are generally used in the lower intermediate and
the entire low temperature ranges. Consideration should be made for fire
retardancy of the material.
2.4.7 REFRACTORY FIBER
Refractory Fiber
insulations are mineral or ceramic fibers, including alumina and silica, bonded
with extremely high temperature inorganic binders, or a mechanical interlocking
of fibers eliminates the need for any binder. The material is manufactured in
blanket or rigid form. Thermal shock resistance is high. Temperature limits
reach 1750°C. The material is non-combustible.
2.4.8 INSULATING CEMENT
Insulating
and finishing cements are a mixture of various insulating fibers and binders
with water and cement, to form a soft plastic mass for application on irregular
surfaces. Insulation values are moderate. Cements may be applied to high
temperature surfaces. Finishing cements or one-coat cements are used in the
lower intermediate range and as a finish to other insulation applications.
Check each manufacturer for shrinkage and adhesion properties
