Lubricant Testing 101 - Copper Corrosion

This video will feature copper corrosion tests, also known as ASTM method D-4048. A copper corrosion test is performed to ensure that a grease will protect the metal surfaces it comes in contact with over time.

The test begins by the technician polishing a copper strip sample. The sample is then totally immersed into a tightly packed sample of grease which is heated in an oven or liquid bath at a specified temperature for a defined period of time. Commonly used test conditions are 100°C +/- 1°C for 24 hours +/- 5 minutes. Both the time and temperature conditions can be varied according to your product application.

At the end of this heating period, the technician will remove the copper strip from the grease, wiping off the excess grease and then washing the copper coupon with acetone. The copper strip is then visually compared to the ASTM Copper Strip Corrosion Standards. This test is subjective as the results are determined by the eyes of the individual technician performing the test. Nye lab technicians are highly skilled in this test as they have conducted countless copper corrosion tests, thus, making them experts.

The technician will report the results as a number followed by a letter according to the ASTM ranges. These ranges include freshly polished, slightly tarnished (1a to 1b), moderately tarnished (2a to 2e), dark tarnish (3a to 3b), and corrosion (4a to 4c).

This test is often performed for automotive companies to determine how suitable a lubricant is for lubricating parts such as bearings that contain copper or copper alloys because corrosion can cause premature bearing failures. While this test does not measure the ability of the grease to inhibit copper corrosion caused by factors other than the grease itself nor does it measure the stability of the grease in the presence of copper, it does ensure that a grease will protect the metal surface it comes in contact with over time.