The chemical durability of an insulation material and its influence on performance

The chemical durability of an insulation system is often one of the most important criteria in system selection. Chemical absorption can not only mechanically destroy an insulation and jeopardize thermal performance, but it can also increase fire risk and structural corrosion. This can have adverse effects on process control, operating costs and overall worker safety around your process piping, equipment and storage tanks.

The potential for chemical attack can come from external sources such as acid rain, salt air or spillage from adjacent equipment, or from the insulated process system. Tanks or piping systems containing corrosive acids come with the danger of possible alkaline solutions or organic solvents leaking at critical points such as joints, valves or flanges. Absorption of these chemicals by certain insulation materials can lead to loss of performance.

Glass & Mineral Fibers

Fiber glass and mineral wool insulations are essentially made from silicate glasses, but these consist of an open fiberous matrix. While the fibers in these materials are composed of relatively inert silicate glasses, the fibers are often coated with organic binders which can be destroyed by chemicals.

Fiberous insulations also exhibit the potential to wick or absorb potentially hazardous materials. Claims of water resistance or water repellency should not be generally equated with chemical resistance or chemical durability. Absorption of flammable liquids can increase fire risks while absorption of caustics and acids can accelerate corrosion potential. The destruction of binders can also decrease the structural integrity and thermal performance of the material.

We can conclude that there are challenges to overcome in both hot and cold applications.

Calcium silicate and perlite are absorbent, and fibrous insulations offer an open glass matrix which can wick or absorb chemicals. Even if these are chemically durable to some reagents, possible absorption risks can lead to decreased thermal efficiency and an increase in safety, fire and corrosion risks.

Lower-temperature insulation materials such as closed-cell organic foams are susceptible to attack by many chemical reagents. Even in situations where the insulation is chemically durable to a particle substance, reagent vapors can still permeate organic foam cell walls and compromise performance.

Cellular glass insulation is manufactured from soda, lime and aluminosilicate, with silica (SiO2) being the major constituent. It is the inert nature of silica that instills cellular glass with its chemical durability. Acids have little effect on silica glasses, with the exception of hydrofluoric acid and, at high temperatures, phosphoric acid.

The chemical durability of bulk glass can be demonstrated by a variety of tests. One test, glass powder solubility (tests include ISO 719-1981, DIN 12111, USP-111) requires grinding glass to a particular particle size, mixing into distilled water, then applying 90 °C to 121 °C (194 °F to 250 °F) heat from 30 minutes to 4 hours. The extracted alkali is then measured as sodium oxide (Na2O) per unit sample weight.

Under the United States and European Pharmacopoeia procedure, cellular glass has been tested and shown to be as chemically durable as Type III pharmaceutical packaging glass.

Examinations of the chemical durability of cellular glass have been carried out periodically to characterize the degree of durability, to develop products with improved durability, and to compare its durability with other insulation products. These examinations have been made in water, various corrosive chemicals and organic solvents.

• Water: Immersion tests have been conducted on cellular glass over the years by numerous investigators. In one recent study, measurements were made for changes in volume, weight and compressive strength, post immersion for 30 days in 24 °C (75 °F) distilled water. No significant changes were found.
• Reagents: In other tests, cellular glass has been exposed to a variety of chemical and organic reagents at room temperature as shown in the durability table on the previous page. Monitoring the same measurements over the same time period as for water, no significant deterioration was noted (with the exception of 10% sodium hydroxide and potassium hydroxide).

These results show that FOAMGLAS® cellular glass insulation was highly resistant to water, concentrated and dilute acids (except hydrofluoric), solvents, salts, hydrocarbons, ketones, ethers and esters. Combined with its impermeability both to reagent liquids and their vapors, cellular glass is often the material of choice for a wide variety of applications where chemical resistance is a key requirement.