Dyplast has just released its latest Technical Bulletin comparing elastomeric insulation with polyisocyanurate insulation in refrigeration pipe applications. This is a rather comprehensive presentation and discussion of facts relevant to the selection of either elastomeric or polyiso in the general temperature range from -40°F to +40°F, yet the conclusions can be extrapolated to other temperature ranges, and process applications such as food & beverage.
The abbreviated conclusions in our Technical Bulletin include:
- Elastomeric insulation has 30-47% poorer thermal conductivity (K-factor) when compared to polyiso (per ASTM C177/518).
- Polyisocyanurate (ISO-C1®) has demonstrably better thermal performance and physical properties that mitigate risks long term and at a lower installed cost.
- Some elastomeric insulant suppliers advertise that their product is “superior” in Austenitic Stainless Steel (ASS) applications since it may have lower leachable chloride content than polyiso, and thus is acclaimed less susceptible to Stress Corrosion Cracking (SCC), YET the facts are:
- The vast majority of refrigerant pipe is carbon steel, with stainless steel and ASS being used less frequently.
- SCC does not occur in carbon steel, non-austenitic stainless steel, or copper!
- It is generally accepted that SCC occurs only at temperatures from 140°F to 250°F in ASS (a temperature range rarely approached in industrial refrigeration), and only when other factors are present (moisture, stress, time, etc.).
- Some elastomeric suppliers have multiple formulations, and some are not clear on actual chloride content.
- At least two elastomeric insulant manufacturers have tables comparing pipe sizes and R-values (i.e. thermal resistance), given a particular insulant thickness that indicates very high R-values.
- These elastomeric R-value tables are somewhat illusory when they indicate R-values up to “20” for a two-inch-thick insulant.
- These high R-values are the result of calculating R-values based on cylindrical geometry, rather than flat, which is the ASTM standard convention for measuring thermal heat flux!
- ASTM protocols measure thermal heat flux (i.e. insulation performance) in flat specimens to avoid confusion regarding the multi-varied geometries in mechanical systems.
- These R-values based on cylindrical geometry are not necessarily a deceptive practice, yet using the same calculations, polyiso always has superior thermal performance!
For more elaborative data, review the Technical Bulletin here.
Indeed, while this Bulletin focuses on refrigeration, the findings apply to adjacent process industries such as food, beverage, pharmaceutical, etc. Dyplast will shortly release a sister-bulletin with a focus on process industries since there are some important differences that may affect insulant selection, primarily including higher temperatures in “process” and possible increased use of austenitic stainless steel. Dyplast concluded that two distinct bulletins were appropriate for refrigeration and process, so it can be fair to each application, yet they are inevitably somewhat redundant. Therefore, in our next blog and newsletter (relating to process), we will readily point out the distinctions. This allows our readers to quickly glean what they may need or delve into the more comprehensive discussion with the subsequent Technical Bulletin.