Subject: Insulation Physical Properties

What are some of the physical properties of thermal insulation materials? ... And why do I care? ....Below-ambient systems are affected by a number of properties that may affect insulation system performance:

Water absorption is the ability of material to absorb and hold liquid water. Water absorption is important on systems that may be exposed to water. This water may come from a number of external sources such as rain, surface condensation or wash down water. The property of water absorption is especially important on outdoor systems.

Water vapor permeability measured in units of perm-inches (ASTM E96) is an indication of the ability a material to allow the passage of water vapor through it. The lower the permeability, the higher is the resistance of the material to water vapor intrusion. Permeance is not a material property. It is a performance evaluation of the test specimen. ASTM E96 has a set of six standard conditions for the test. It is important to be aware that no two different test conditions are likely to yield the same test results on the same material. Water vapor can penetrate all but a few materials. Therefore, in order to make accurate comparisons the materials being compared must be tested using identical conditions.

Water vapor permeability can be a critical design consideration because water vapor has the ability to penetrate materials that are unaffected by water in the liquid form. Water vapor intrusion is a particular concern to insulation systems subjected to a thermal gradient. Driving forces are created due to vapor pressure differences between ambient conditions and the colder operating conditions of the piping. These forces drive water vapor into the insulation system, where it may be retained as water vapor, condense to liquid water or condense and freeze to form ice. Thermal properties of insulation materials are negatively affected as the moisture or vapor content of the insulation material increases.

Wicking is the tendency of an insulation material to absorb liquid due to capillary action. Wicking is measured by partially submerging a material and measuring both the amount of liquid that is absorbed, and the amount of space by volume the liquid has consumed within the insulation material.

Thermal expansion/contraction is a concern both for insulation systems that operate continuously at below ambient conditions or systems that cycle between below-ambient conditions and elevated temperatures. The coefficient of expansion or contraction is the material property which measures its dimensional change relative to a change in its temperature.

When heated or cooled, materials, such as steel, will expand or contract at a constant rate. These changes are reversible, since the materials will return to their original dimension when their temperature returns to where it was before being heated or cooled. This reversibility distinguishes coefficient of expansion (contraction) from the two properties relating to dimensional changes; dimensional stability and linear shrinkage: neither of which is reversible.

Not all insulation materials exhibit the ability to return to their original size. It is limited to cellular glass and rigid organic foams such as: phenolic, extruded polystyrene and polyisocyanurate. When designing expansion and contraction joints for the system; the amount of movement that can be accommodated by an expansion joint, along with the differential movement between the insulation and the substrate, are needed when determining the joint spacing.

A large difference in the amount of contraction between the insulation and the piping may result in open joints of the insulation system. These open joints not only create a thermal short circuit at that point in the system, but may also affect the integrity of the entire system. Insulation materials that have large contraction coefficients, and do not have a high enough tensile strength or compressive strength to compensate, may experience shrinkage and subsequent cracking within the material.

At the elevated temperature end of the cyclic process, the reverse is considered. High thermal expansion coefficients may result in warping or buckling of a material that for some insulation materials is permanent and irreversible. In this instance, the possibility of resulting stress on an external vapor retarder or weather barrier should be considered.

Dimensional stability is the material property that indicates its ability to retain its size or shape after aging, cutting or being subjected to temperature or moisture. This property is generally associated with rigid organic cellular foams which are used in low temperature service. These changes are not reversible and can affect the ease of installation and could produce adverse effects in the installed system.

Compressive strength is the value of the compressive stress required to crush or excessively deform an insulation material. Deformation is usually considered unacceptable if permanent, or in other words the material does not spring-back or recover from the deformation when the load is removed. Unfortunately, many insulation materials exhibit no elasticity or resilience.

Compressed insulation cells typically reduces the insulation value of the material in the compressed area. In the design of cold piping or tanks, high compressive strength insulation must be used on pipe shoes or tank bottoms to transmit the weight of the piping or equipment.

The compressive strength of most materials change with temperature, so the in-service property can be greatly different than the strength measured at room temperature and reported on the data sheet. Consult the manufacturer for pertinent data.

Density is the weight of a unit volume of insulation. It is necessary to know the density to calculate loadings and the heating rate when mass is one of the functions.

EXTOL INSULATION SYSTEMS: COMPLETE PRODUCT LINE    COMPOSITE INSULATIONS    CONTOURED HEAD SYSTEMS    EXCEL-LAP SYSTEMS    ISOWRAP® PRECISION CUT    TRACED LINE SYSTEMS    VALVE & JACKET SYSTEMS

DATA SECTIONS: DESIGN & INSTALLATION TIPS ESTIMATING TIPS / & CHARTS EXTOL SYSTEMS DATA MSDS LISTED BY MANUFACTURER MSDS LISTED BY PRODUCT TYPE PRODUCT DATA SHEETS PUBLICATIONS & ARTICLES HELPFUL SALES/TRAVEL INFO WBE CERTIFICATIONS

BACK TO MAIN OBTAIN A QUOTE SURPLUS MATERIAL PLACE AN ORDER EMPLOYMENT OPPORTUNITIES PASSKEY SECTION: WAIVER / PASSKEY REQUEST INSULATION SPECIFICATIONS DETAILED DRAWINGS_COLD/HOT