Scoring Damage Caused by Chipping of Chromium Plating on a Cylinder

Several large chromium-plated 4340 steel cylinders were removed from service because of deep longitudinal score marks in the plating. One of the damaged cylinders and a mating cast aluminum alloy B850-T5 bearing adapter that also exhibited deep longitudinal score marks were submitted for examination. Analysis (visual inspection, manual testing of the hardness and adherence of the chromium plating, 100x microscopic examination, and hardness testing) supported the conclusions that high localized loads on the cylinder had resulted in chipping of the chromium plating, particles of which became embedded in the aluminum alloy adapter. The sliding action of the adapter with embedded hard particles resulted in scoring of both the cylinder and the adapter. If the cylinder alone had been available for examination, it might have been concluded that the scoring had been caused by entrapped sand or debris from an external source. No recommendations were made.