Theory and Method
The copper strip corrosion test reveals reactive sulfur compounds left in a petroleum product after refining. Species such as free sulfur, hydrogen sulfide, and mercaptans react with the copper surface and build up copper sulfide and copper oxide films. Those films tarnish the strip, and the shade and pattern of the discoloration correspond to the strength and amount of the corrosive agents. The relationship does not follow total sulfur content, because the chemical form of the sulfur decides how strongly it corrodes copper.
To run the test, the operator polishes a copper strip to a clean finish, submerges it in a metered volume of sample, and holds it at a fixed temperature for a set time. Volatile fuels go into a sealed pressure vessel that stops evaporation, while heavier products test in an open tube. The QualiCCT™ D131 warms both formats in one stainless steel bath and stirs the medium so all positions track the same temperature. Uniform heat and steady control give the reproducible conditions ASTM D130 calls for.
When the exposure ends, the operator lifts out the strip, washes it, and matches it to the ASTM Copper Strip Corrosion Standard color scale. Ratings run from 1a, a light tarnish, up to class 4, which marks heavy corrosion or blackening. That grade tells the buyer whether the product will stay safe for copper and copper alloy parts in service. Since the reading depends on the eye, the tight temperature hold of the QualiCCT™ D131 cuts run-to-run variation.
