Understanding Heat Transfer Oil Analysis Reports

So, you have sent out a sample of your used heat transfer fluid and ordered a basic analysis or laboratory test. Most heat transfer fluid vendors (including Relatherm Heat Transfer Fluids) offer this service on a complimentary basis.  A few days pass by and the verdict is out. You have your fluid analysis report. How should you interpret it? What do the different values and parameters mean? Here are some tips on how to digest that report.

Total Acid Number (TAN) – This value is indicative of the quantity of acidic compounds in your heat transfer fluid. These acidic compounds are byproducts of fluid oxidation. Oxidation occurs when your thermal fluid is exposed to air.  TAN is determined by the amount of Potassium Hydroxide (KOH) base required to neutralize the acid in one gram of a heat transfer fluid sample. The standard unit of measure is mg KOH/g. A virgin fluid typically has a TAN of 0.01 mg KOH/g or less. If your laboratory analysis returns a TAN value higher than 1.0 mg KOH/g, it is time to change your heat transfer fluid. More importantly, a drastic increase in TAN a short while after virgin fluid is added in should cause you to open an investigation into system-related cause(s) of rapid oxidation.

Flash Point – This is the lowest temperature at which your heat transfer fluid will form a vapor in the air near its surface that will “flash,” or briefly ignite, on exposure to an open flame. Since the flash point of any heat transfer fluid is related to fire safety and process safety management, the higher the flash point, the better. You should watch out for significant decreases in flash point. If this happens, it could be a pointer to the possibility of thermal cracking (overcooking of the thermal fluid).

Viscosity – The viscosity of your thermal fluid is an important parameter that must not be overlooked. A drastic increase or decrease in viscosity is an indicator of fluid degradation. If you observe an unexplained increase in viscosity, couple with an increase in TAN, then you should suspect fluid oxidation as a degradation pathway. On the other hand, a rapid decrease in viscosity coupled with a decrease in Flash Point points to thermal cracking

Visual & Olfactory Observation – Virgin heat transfer oils are typically clear in appearance. Fluid degradation causes this clear appearance to darken over time. A sharp burnt smell may lead one to believe that the fluid is cracked. A pungent odor is generally indicative of fluid oxidation.

If you have questions about your heat transfer oil, our Thermal Fluids Experts are always on standby to assist you.