3 Things Engineers Overlook in Insulation Material Selection

When it comes to designing a high-temperature industrial system, engineers and specifiers have a lot on their plate. It’s their responsibility to make sure the whole system works smoothly, efficiently, and safely.  A crucial part to making the high-temperature system operate efficiently and safely is the correct insulation material selection. However, given the number of variables that go into designing a successful insulation system, it can be easy to glance over or even neglect certain aspects of insulation system design for the sake of expediency or cost.  In addition, engineers and specifiers may not be sufficiently familiar with the specifications of certain materials or the manufacturers may not provide all appropriate performance data and information. We all understand that two of the primary purposes for insulation are to improve efficiency and process control and to ensure a safe working environment by maintaining standards for personnel protection. As we look at these two primary objectives, it’s important to understand how the insulation will operate in varying circumstances as well as how the published performance data correlate to real-world applications. Let’s take a look at three of the key factors that can often get a little muddied when designing high-temperature insulation systems...

Insulation Thickness & Layers: In terms of energy efficiency and process control, one of the primary factors that dictates thermal performance is insulation thickness. Ultimately, once installed, all insulation materials are required to meet specific surface temperature standards – the primary difference among the materials comes down to how thick they need to be in order to maintain these temperatures and subsequently, how many layers of the insulation need to be installed to achieve that thickness. For example, the table below indicates how thick several insulations need to be in order to maintain Safe-To-Touch surface temperatures (140°F as recommended by ASTM C1055: The Standard Guide for Heated system Surface Conditions that Produce Contact Burn Injuries) on an 800°F pipe*. It also includes the number of layers of insulation would be required in order to achieve the appropriate thickness. Calcium silicate is inherently thicker than silica aerogel. As a result, it can achieve the necessary thermal performance with only two layers of insulation, while it would require five layers of silica aerogel to attain the same performance.

*12” pipe/ambient air temp 75°F/jacketed(ɛ = 0.10)/ wind speed = 2.5 mph Though layers make a difference in terms of the performance of the insulation system, it’s key to remember that whenever additional layers are needed there will be added cost for both installation labor and materials, as well as added weight.

So let’s talk about that yellow line that references thermal shift. Material Composition: An insulation’s thermal performance is also a function of its physical composition. For example, when silica aerogel is exposed to temperatures that exceed 300°F for several hours, the aerogel within the insulation begins to fracture, permanently compromising the material’s thermal performance. This decrease in thermal performance is called thermal shift, and is not accounted for in manufacturers’ data sheets. In some cases, silica aerogel can see a 20% decline in thermal performance, allowing more heat to pass through the insulation at the expense of system efficiency and personnel safety.  Fortunately, this issue can be addressed by adding additional layers of silica aerogel insulation, as shown in the yellow row in the table above. Bear in mind that silica aerogel isn’t the only insulation that can experience damage after installation. The binder in mineral wool can burn out at high temperatures. While this doesn’t directly affect the thermal performance, it does affect the compressive strength of the insulation. This makes the mineral wool vulnerable to impact damage, which has the potential to affect thermal performance. System Configuration: The system configuration is intricately connected to an insulation’s thermal performance. Specifically, insulation will provide better thermal performance in a flat configuration than it will in a round configuration. Since the insulation performance is better for flat configurations than it is for round configurations, it’s important to know which test method the manufacturer references in their data sheets. Most manufacturers will typically use two tests to determine their products’ thermal performance: 1. ASTM C335 – Standard Test Method For Steady-State Heat Transfer Properties Of Pipe Insulation (round configuration) 2. ASTM C518 – Standard Test Method For Steady-State Thermal Transmission Properties By Means Of The Heat Flow Meter Apparatus (flat configuration) If an insulation system for a pipe application is designed using data from the ASTM C518 flat application test, the insulation thickness specified will not be sufficient to achieve the intended thermal performance or maintain personnel protection and safety standards. As such, it’s is essential to confirm that the data on the data sheet is the correct data for the intended application, and should remain a crucial part of your insulation material selection process. Looking at all the variables that go into system design, it can be easy to gloss over some of the important details with industrial insulation material selection. Equipping yourself to understand the details of the data can help ensure that your design is optimized for efficiency and safety. To learn more about thermal shift, click here.