How well (or how poorly) does lab testing reflect real-world manufacturing conditions?
In the real world, oxidation of heat transfer fluids occurs in a vented reservoir or expansion tank that for whatever reason is hot (>70°C).
The acids formed in the expansion tank subsequently circulate through the system, decomposing in the heater and producing carbon sludge.
To determine which of several tests is more representative of the real world, several brands of fluid that contain additive packages were tested with the following methods:
- A modified D-2440 test running at 200°C with 15 liters/hour oxygen for 24 hours – essentially an IP-48 (Institute of Petroleum Standards) test.
- The standard ASTM D-2440 test running at 100°C with 1 liter/hour oxygen for 164 hours.
Fluid Sample Prepared for Oxidation Testing
The IP-48 test trashed all of the fluids. Acid Numbers ranged from 1.9 to 3.9 mg KOH/g sample (normal upper limit is 0.4). Sludge ranged from 14 to 18 weight % (any sludge is a problem).
Prepared Sample In Heating/Oxygen Apparatus
The results of the D2440 test were more representative of what is expected from additized heat transfer fluids. Acid Numbers were 0.01 to 0.03 mgKOH/g sample and Sludge was less than 0.1 weight %. We also tested fluids that contained no additive packages using the D-2440. Acid Numbers were at least 30 mg KOH/g sample and Sludge was at least 1.5 weight %.