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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.