0.5-1 at 10%


Open cell

(a) P/C means pipe covering.

(a) P/C means pipe covering.

Sources: Refs. 17, 18 and manufacturers' literature.

Temperature-Use Range

Since all products have a point at which they become thermally unstable, the upper temperature limit of an insulation is usually quite important. In some cases the physical degradation is gradual and measured by properties such as high-temperature shrinkage or cracking. In such cases, a level is set for the particular property and the product is rated to a temperature at which that performance level is not exceeded. Occasionally, the performance levels are established by industry standards, but frequently, the manufacturers establish their own acceptance levels based on their own research and application knowledge.

In other cases, thermal instability is very rapid rather than gradual. For example, a product containing an organic binder may have a certain temperature at which an exothermic reaction takes place due to a too-rapid binder burnout. Since this type of reaction can be catastrophic, the temperature limit for such a product may be set well below the level at which the problem would occur.

Low-end temperature limits are usually not specified unless the product becomes too brittle or stiff and, as such, unusable at low temperatures. The most serious problem with low-temperature applications is usually vapor transmission, and this is most often related to the vapor-barrier jacket or coating rather than to the insulation. In general, products are eliminated from low-temperature service by a combination of thermal efficiency and cost.

Thermal Conductivity

This property is very important in evaluating insulations since it is the basic measure of thermal efficiency, as discussed in Section 15.1.1. However, a few points must be emphasized. Since the k value changes with temperature, it is important that the insulation mean temperature be used rather than the operating temperature. The mean temperature is the average temperature within the insulation and is calculated by summing the hot and cold surface temperatures and dividing by 2: (th + ts)/2. Thermal conductivity data are always published per mean temperature, but many users incorrectly make comparisons at operating temperatures.

A second concern relates to products which have k values that change with time. In particular, foam products often utilize an agent that fills the cells with a gas heavier than air. Shortly after manufacture, some of this gas migrates out, causing an increase in thermal conductivity. This new value is referred to as an "aged k" and is more realistic for design purposes.

Compressive Strength

This property is important for applications where the insulation will see a physical load. It may be a fulltime load, such as in buried lines or insulation support saddles, or it may be incidental loading from foot traffic. In either case, this property gives an indication of how much deformation will occur under load. When comparing products it is important to identify the percent compression at which the compressive strength is reported. Five and 10% are the most common, and products should be compared at the same level.

Fire Hazard Classification

Insulation materials are involved with fire in two ways: fire hazard and fire protection. Fire protection refers to the ability of a product to withstand fire exposure long enough to protect the column, pipe, or vessel it is covering. This topic is discussed in Section 15.3.1.

Fire hazard relates to the product's contribution to a fire by either flame spread or smoke development. The ASTM E-84 tunnel test is the standard method for rating fire hazard and compares the FS/SD (flame spread/smoke developed) to that of red oak, which has a 100/100 rating. Typically, a 25/50 FHC is specified where fire safety is an important concern. Certain concealed applications allow higher ratings, while the most stringent requirements require a noncombustible classification.

Cell Structure

The internal cell structure of an insulation is a primary factor in determining the amount of moisture the product will absorb as well as the ease in which vapor will pass through the material. Closed-cell structures tend to resist both actions, but the thickness of the cell walls as well as the base material will also influence the long-term performance of a closed-cell product. In mild design conditions such as chilled-water lines in a reasonable ambient, closed-cell products can be used without an additional vapor barrier. However, in severe conditions or colder operating temperatures, an additional vapor barrier is suggested for proper performance.

Available Forms

An insulation material may be just right for a specific application, but if it is not manufactured in a form compatible with the application, it cannot be used. Insulation is available in different types (Ref. 19).

Loose-fill insulation and insulating cements. Loose-fill insulation consists of fibers, powders, granules or nodules which are poured or blown into walls or other irregular spaces. Insulating cements are mixtures of a loose material with water or other binder which are blown on a surface and dried in place.

Flexible, semirigid and rigid insulation. Flexible and semirigid insulation, which are available in sheets or rolls, are used to insulate pipes and ducts. Rigid insulation is available in rectangular blocks, boards or sheets and are also used to insulate pipes and other surfaces. The most common forms of insulation are flexible blankets, rigid boards and blocks, pipe insulation half-sections and full-round pipe sections.

Formed-in-place insulation. This type of insulation can be poured, frothed or sprayed in place to form rigid or semirigid foam insulation. They are available as liquid components, expandable pellets or fibrous materials mixed with binders.

Removable-reusable insulation covers. Used to insulate components that require routine maintenance (like valves, flanges, expansion joints, etc.). These covers use belts, Velcro or stainless steel hooks to reduce the installation time.

Other Properties

For certain applications and thermal calculations, other properties are important. The pH of a material is occasionally important if a potential for chemical reaction exists. Density is important for calculating loads on support structures and occasionally has significance with respect to the ease of installation of the product. The specific heat is used together with density in calculating the amount of heat stored in the insulation system, primarily of concern in transient heat-up or cool-down cycles.

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