DEFINITION OF INSULATION
Insulation is 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 a process.
4. Prevent vapor 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 USDA (FDA) criteria in food and cosmetic
plants.
The temperature range within which
the term "thermal insulation" will apply, is from -73.3ºC (-100ºF) to 815.6ºC
(1500ºF). All applications below -73.3ºC (-100ºF) are termed "cryogenic," and
those above 815.6ºC (1500ºF) are termed "refractory."
Thermal insulation is further
divided into three general application temperature ranges as follows:
A. Low Temperature Thermal
Insulation
1. 15.6ºC through 0ºC (60ºF
through 32ºF) -- i.e. Cold or chilled water.
2. -0.6ºC through -39.4ºC (31ºF through -39ºF) -- i.e. Refrigeration or glycol.
3. -40.0ºC through -73.3ºC (-40ºF through -100ºF) -- i. e. Refrigeration or brine.
4. -73.9ºC through -267.8ºC (-101ºF through -450ºF) -- i. e. cryogenic.
B. Intermediate
Temperature Thermal Insulation
1. 16.1ºC through 99.4ºC (61ºF
through 211ºF) -- i.e. Hot water and steam condensate.
2. 100.0ºC through 315.6ºC (212ºF through 600ºF) -- i.e. Steam, high temperature hot
water.
C. High Temperature
Thermal Insulation
1. 316.1ºC through 815.6ºC
(601ºF through 1500ºF) -- i.e. Turbines, breechings, stacks, exhausts, incinerators,
boilers.
GENERIC TYPES AND FORMS OF INSULATION
Insulation will be discussed in this manual according to its generic types and
forms. 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 insulation).
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TYPES
1. Fibrous Insulation: Composed of small diameter fibers which finely
divide the air space. The fibers may be perpendicular or horizontal 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 insulation of this type are glass
fiber and mineral wool.
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),
polyurethane, polyisocyanurate, plyolefin, and elastomeric.
3. Granular
Insulation: Composed of small nodules which 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 to make a rigid insulation. Examples of these insulations are
calcium silicate, expanded vermiculite, perlite, cellulose, diatomaceous earth and
expanded polystyrene.
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FORMS
Insulation is 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 segment, 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. Foam: Poured
or froth foam used to fill irregular areas and voids. Spray used for flat surfaces.
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PROPERTIES OF INSULATION
Not all properties are significant for all materials or applications. Therefore,
many are not included in manufacturers' published literature or in the Table of Properties
which follows in this section. In some applications, however, omitted properties may
assume extreme importance (i.e. when insulations must be compatible with chemically
corrosive atmospheres.)
If the property is significant for
an application and the measure of that property cannot be found in manufacturers'
literature, effort should be made to obtain the information directly from the
manufacturer, testing laboratory, or insulation contractors association.
The following properties are
referenced only according to their significance in meeting design criteria of specific
applications. More detailed definitions of the properties themselves can be found in the
Glossary (Section XI).
1. THERMAL PROPERTIES OF
INSULATION
Thermal properties are the primary consideration in choosing insulations.
Refer to the Glossary for definitions.
a. Temperature limits: Upper
& lower temperatures within which the material must retain all its properties.
b. Thermal conductance
"C": The rate of heat flow for the actual thickness of a material.
c. Thermal conductivity
"K": The rate of heat flow based on 25 mm (one inch) thickness.
d. Emissivity
"E": Significant when the surface temperature of the insulation must be
regulated as with moisture condensation or personnel protection.
e. Thermal resistance
"R": The overall resistance of a "system" to the flow of
heat.
f. Thermal transmittance
"U": The overall conductance of heat flow through a "system".
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 corrosive atmospheres are present. Also insulation
must not contribute to corrosion of the system. See Section III.
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.
d. Capillarity:
Must be considered when material may be in contact with liquids.
e. Chemical reaction:
Potential fire hazards exist in areas where volatile chemicals are present. Corrosion
resistance must also be considered.
f. Chemical resistance:
Significant when the atmosphere is salt or chemical laden.
g. Coefficient of
expansion and contraction: Enters into the design and spacing of
expansion/contraction joints and/or the 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 affects other properties of that material, especially thermal
properties.
k. Dimensional stability:
Significant when the material is exposed to atmospheric and mechanical abuse such as
twisting or vibration from thermally expanding pipe.
l. Fire retardancy: Flame
spread and smoke developed ratings should be considered.
m. Hygroscopicity:
Tendency of a material to absorb water vapor from the air.
n. Resistance to
ultraviolet light: Significant if application is outdoors.
o. Resistance to fungal or
bacterial growth: Is necessary in food or cosmetic process areas.
p. Shrinkage:
Significant on applications involving cements and mastics.
q. Sound absorption
coefficient: Must be considered when sound attenuation is required, as it is in
radio stations, some hospital areas, etc.
r. Sound transmission loss
value: Significant when constructing a sound barrier.
s. Toxicity: Must
be considered in food processing plants and potential fire hazard areas.
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MAJOR INSULATION MATERIALS
The following is a general inventory of the characteristics and properties of major
insulation materials used in commercial and industrial installations. See the Insulation
Property Tables at the end of Section II for a comparative review.
1. CALCIUM
SILICATE
Calcium silicate is a granular insulation made of lime and silica,
reinforced with organic and inorganic fibers and molded into rigid forms. Service
temperature range covered is 37.8ºC to 648.9ºC (100ºF to 1200ºF). Flexural strength is
good. Calcium silicate is water absorbent. However, it can be dried out without
deterioration. The material is noncombustible and used primarily on hot piping and
surfaces. Jacketing is field applied.
2. GLASS
a. Fibrous: Available
as flexible blanket, rigid board, pipe insulation and other pre-molded shapes. Service
temperature range is -40.0ºC to 37.8ºC (-40ºF to 1000ºF). Fibrous glass is neutral;
however, the binder may have a pH factor. The product is noncombustible and has good sound
absorption qualities.
b. Cellular: Available
in board and blºCk form capable of being fabricated into pipe insulation and various
shapes. Service temperature range is -267.8ºC to 482.2ºC (-450ºF to 900ºF). Good
structural strength, poor impact resistance. Material is noncombustible, non-absorptive
and resistant to many chemicals.
3. MINERAL
FIBER (ROCK AND SLAG WOOL)
Rock and/or slag fibers are bonded together with a heat resistant binder
to produce mineral fiber or wool available in loose blanket, board, pipe insulation, and
molded shapes. Upper temperature limit can reach 1037.8ºC (1900ºF). The material has a
practically neutral pH, is noncombustible, and has good sound control qualities.
4. EXPANDED
SILICA, OR PERLITE
Perlite is made from an inert siliceous volcanic rock combined with water.
The rock is expanded by heating, causing the water to vaporize and the rock volume to
expand. This creates a cellular structure of minute air cells surrounded by vitrified
product. Added binders resist moisture penetration and inorganic fibers reinforce the
structure. The material has low shrinkage and high resistance to substrate corrosion.
Perlite is noncombustible and operates in the intermediate and high temperature ranges.
The product is available in rigid pre-formed shapes and blocks.
5.
ELASTOMERIC
Foamed resins combined with elastomers produce a flexible cellular
material. Available in pre-formed shapes and sheets, elastomeric insulations possess good
cutting characteristics and low water and vapor permeability. The upper temperature limit
is 104.4ºC (220ºF). Elastomeric insulation is cost efficient for low temperature
applications with no jacketing necessary. Resiliency is high. Consideration should be made
for fire retardancy of the material.
6. FOAMED
PLASTIC
Insulation 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 moisture resistance and cutting
characteristics. The chemical content varies with each manufacturer. Available in
pre-formed shapes and boards, foamed plastics are generally used in the low and lower
intermediate service temperature range -182.8ºC to 148.9ºC (-297ºF to 300ºF).
Consideration should be made for fire retardancy of the material.
7. REFRACTORY
FIBER
Refractory fiber insulations are mineral or ceramic fibers, including
alumina and silica, bound with extremely high temperature binders. The material is
manufactured in blanket or rigid form. Thermal shock resistance is high. Temperature
limits reach 1648.9ºC (3000ºF). The material is noncombustible.
The use and design of
refractory range materials is an engineering art in its own right and is not treated fully
in this manual, although some refractory products can be installed using application
methods illustrated here.
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.
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