Selecting an Insulation - Communication is Key
The owner, engineer, general contractor, insulation contractor and insulation
and accessories manufacturers must communicate with each other from the
very beginning of a project in order to minimize problems in the stages
of design, specification preparation, construction, operations, and maintenance.
Open and frank discussion between all parties is critical to helping the
engineer establish the proper design criteria, define pipe and duct dimensions,
select the insulation materials types and thicknesses, facings or jackets,
and define the installation procedures to be followed. Ambiguities and
omissions diminish when communications is encouraged.
Such
a discourse, along with knowledge of the most important insulation criteria
as detailed below, will aid the engineer in calculating the thicknesses
required for the intended service.
Characteristics of Insulation
Insulations have different properties and limitations depending upon the
service, location, and required longevity of the application. These are
taken into account by engineers when considering the insulation needs
of an industrial or commercial application.
Thermal
Resistance
The quantity determined by the temperature difference, at steady state,
between two defined surfaces of a material or construction that induces
a unit heat flow rate through a unit area. A resistance associated with
a material shall be specified as a material R. A resistance associated
with a system or construction shall be specified as a system R.
Apparent
Thermal Conductivity
A thermal conductivity assigned to a material that exhibits thermal transmission
by several modes of heat transfer resulting in property variation with
specimen thickness or surface emittance.
Thermal
Conductivity (commonly referred to as 'k')
The time rate of steady state heat flow through a unit area of a homogenous
material induced by a unit temperature gradient in a direction perpendicular
to that unit area. Materials with lower k factors are better insulators.
Density
This is the weight of a specific volume of material measured in pounds
per cubic foot (kilograms per cubic meter).
Surface
Burning Characteristics
These are comparative measurements of flame spread and smoke development
with that of select red oak and inorganic cement board. Results of this
test may be used as elements of a fire-risk assessment which takes into
account all of the factors which are pertinent to an assessment of the
fire hazard or fire risk of a particular end use.
Compressive
Resistance
This is a measure of the material to resist deformation (reduction in
thickness) under a compressive load. It is important when external loads
are applied to an insulation installation. Two examples are deforming
the insulation on a pipe at a Clevis type hanger due to the combined weight
of the pipe and its contents between the hangers and....Resistance of
an insulation to compress on an outdoor rectangular duct due to heavy
mechanical loads from external sources such as wind, snow, or occasional
foot traffic.
Thermal
Expansion/Contraction and Dimensional Stability
Insulation systems are installed under ambient conditions that may differ
from service conditions. When the operating conditions are imposed, metal
surfaces may expand or contract differently from the insulation and finish
applied. This can create openings and parallel heat flow and moisture
flow paths that can degrade system performance.
Long
term satisfactory service requires that the insulating materials, closure
materials, facings, coating, and accessories withstand the rigors of temperature,
vibration, abuse, and ambient conditions without adverse loss of dimensions.
Water
Vapor Permeability
This is the time rate of water vapor transmission through unit area of
flat material of unit thickness induced by unit vapor pressure difference
between two specific surfaces, under specified temperature and humidity
conditions. It is important when insulation systems will be operating
with service temperatures below the ambient air. Materials and systems
with low water vapor permeability are needed in this service.
Cleanability
Ability of a material to be washed or otherwise cleaned to maintain its
appearance.
Temperature
Resistance
Ability of a material to perform its intended function after being subjected
to high and low temperatures which the material might be expected to encounter
during normal use.
Weather
Resistance
Ability of a material to be exposed for prolonged periods of time to the
outdoors without significant loss of mechanical properties.
Abuse
Resistance
Ability of a material to be exposed for prolonged periods of time to normal
physical abuse without significant deformation or punctures.
Ambient
Temperature
The dry bulb temperature of surrounding air when shielded from any sources
of incident radiation.
Corrosion
Resistance
Ability of a material to be exposed for prolonged periods of time to a
corrosive environment without significant onset of corrosion and the consequential
loss of mechanical properties.
Fire
Resistance/Endurance
Capability of an insulation assembly exposed for a defined period of exposure
to heat and flame (fire) with only a limited and measurable loss of mechanical
properties. Fire endurance is not a comparative surface burning characteristic
for insulation materials.
Fungal
Growth Resistance
Ability of a material to be exposed continuously to damp conditions without
the growth of mildew or mold.
