Polyisocyanurate vs. cellular glass

LNG Industry Q&A with Jim Young, Cold Insulation Specialist Engineer at Johns Manville.

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What are the differences between polyisocyanurate (PIR) and cellular glass insulations? Is one better for liquified natural gas (LNG) pipe insulation applications?

Polyisocyanurate (PIR) and cellular glass are the two most common materials used to insulate LNG pipes. While these two insulation materials are very different, both are successfully used in LNG applications and have long service lives. Cellular glass is exactly what it sounds like &#; glass, an inorganic material that contains a myriad of closed cells. PIR is an organic material that is blown to create a foam, also containing closed cells. While both products are insulating materials, they differ in many of their properties.

Before describing the specific properties of these insulations, it is important to realise that there is no single best pipe insulation material; every material has advantages and disadvantages. When selecting an insulation material, specifiers should weigh the advantages and disadvantages against their relative importance for the specific project along with the history of successful use of the material in similar applications.

The two main advantages of cellular glass as LNG pipe insulation are its water resistance and its low flammability. Since cellular glass is made entirely of closed glass cells, it offers very good resistance to both liquid water and water vapour infiltration. However, the presence of joints and the possibility of breakage present weak points in its water resistance. As a result, vapour retarders must still be used with a cellular glass insulation system, as they are with every other LNG pipe insulation system.

Being inorganic, cellular glass is also non-combustible. However, the accessory products used with cellular glass, including joint sealants and vapour retarders, are organic. This means that the completed cellular glass insulation system does not have the same combustibility performance as the cellular glass insulation alone. Further, LNG applications typically do not require the use of a non-combustible insulation. Instead, specifications usually identify only a specific flame spread index of &#;25 (measured by the ASTM E84 test). Both cellular glass and PIR meet this requirement.

The main advantages of PIR insulation are its lower (better) thermal conductivity and its significantly lower total installed cost compared to cellular glass. When compared to PIR, cellular glass has a thermal conductivity that is 25 &#; 65% higher (worse) than PIR. This difference in thermal conductivity directly translates into less insulation thickness needed when using PIR. This also means that PIR insulation systems have a smaller outer circumference than cellular glass systems by approximately 10 &#; 20%. As a result, PIR systems need less of the expensive accessory products like vapour retarders, joint sealant, and metal jacketing than cellular glass systems.

Additionally, PIR insulation both costs less per board foot than cellular glass and has lower installation costs. PIR is easier to fabricate and install, and it comes in longer pipe shells/segments (3 ft long) than cellular glass (2 ft long). This means that installers have fewer joints to address when installing PIR, so they can move more quickly, thereby reducing installation costs. Overall, PIR insulation systems require less insulation, have lower material costs, use less of the expensive accessory materials, and are easier to fabricate and install. As a result, the total installed cost savings of using PIR over cellular glass can be substantial.

The main disadvantage of PIR is that while it is closed cell, it is not as water resistant as cellular glass. Any concern with the water and water vapour resistance of PIR is eliminated by properly designing and installing the full insulation system, which is required for both PIR and cellular glass. A full insulation system includes dual vapour retarders, fully sealed joints between insulation pieces, vapour stops at key locations, and a properly installed outer protective jacket system.

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The old adage, 'nothing succeeds like success,' is also true for insulation systems. For many years, both PIR and cellular glass insulation systems have been used extensively and successfully in LNG pipe insulation applications throughout the world. Both materials are excellent insulation options when they are part of a well-designed, properly installed system.

JM recognises that LNG systems have unique requirements and variables and they have developed a digital library of resources all in one spot on their website, visit their page Insulation for Cryogenic and LNG Systems. You'll find resources to help you determine which material is right for your application, including blogs that answer four more frequently asked questions about insulating LNG systems.

Written by Kim Melton, Assoc. Content Marketing Manager & Technical Writer at Johns Manville.

Read the article online at: https://www.lngindustry.com/special-reports//polyisocyanurate-vs-cellular-glass/

Whether for exterior insulation of the facade or the roof under the roof covering, or as an insulating material in the interior of ceilings or walls, cellular glass has excellent insulating properties. It consists of 66 percent recycled waste glass, mostly from window or car glass panes. This is first melted in energy-saving low-temperature furnaces using additives such as feldspar or sodium carbonate. The cooled mixture is ground together with carbon in ball mills and then heated at over 1,000 degrees, causing it to foam into a cell structure with cell walls.

Foam glass has many advantages. Due to its low thermal conductivity, foam glass insulation keeps the heat in the house. In addition, foam glass is waterproof and vapor-tight as long as the foam glass panels are undamaged. Under these conditions, the building material can therefore be used excellently in areas where a high level of moisture formation is to be expected, as the boards do not absorb water. However, if there are small bubbles on the surface of the sheets, water could penetrate and freeze. If the volume of the frozen bubbles increases, the cell structure may crack and cracks may form in the foam glass walls. As a result, over time, the insulating effect may be reduced as the thermal conductivity increases.

As a building material, foam glass meets the highest fire protection requirements. According to DIN -1 and EN -1, cellular glass insulations belong to class A1, the highest building material class in the area of fire protection, as they do not contain any combustible substances. However, anyone who attaches great importance to good sound insulation should resort to other sound-absorbing solutions, as foam glass does not have good sound insulation properties. Other advantages include a high load-bearing capacity and a very good ecological balance compared with synthetic building materials. Commercially available sheets cost between 40 and 60 euros per square meter.

Source: Housing Happiness
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