Does lab testing tell the whole story?
There are a number of accelerated aging laboratory tests that are designed to determine oxidation-inhibitor performance and longevity. Most involve bubbling pure oxygen through a heated sample that has an oxidation catalyst (usually copper wire) submerged in it. The effectiveness of the additive is determined by measuring the byproducts of degradation — sludge formation, acid-number increase and viscosity increase — at the end of the test.
Oxidation Stability Apparatus (Photo courtesy of Koehler Instrument Co., Inc.)
Older tests (such as IP 48) that utilized a high oxygen flow-rate for a short period of time have been superseded by longer duration but lower oxygen flow-rate tests (such as ASTM D2440) that have proven to be more representative of real-life oxidation conditions in lubricating oils. While the D2440 test is not completely applicable to heat transfer fluids (which are exposed to even less oxygen than lubricating oils in service,) it must suffice because there exists no specific oxidation test method for heat transfer fluids. ASTM D2440 and other newer methods are also more accurate than the older tests.
Next post: Discussion; How well (or poorly) does lab testing reflect real world conditions?
Read it here: Air and Heat Transfer Fluids Part 3