Effects of Inhibited Acid Cleaning of Steel Fracture Surfaces for Failure Analyses

To Clean Or Not To Clean? In many failure analyses, adherent rust limits the scope of the fracture surface examinations and presents dilemmas for the failure analyst. The rust must be removed to identify fracture initiation sites and crack propagation modes, and the cleaning methodology varies with service life and type of environmental exposure that the component experienced. In this study, failure analysts examined laboratory fracture samples in a scanning electron microscope (SEM). The fractures were then subjected to controlled rusting conditions, and subsequently varying exposures to inhibited acid were used to remove the rust. The fracture surfaces were again examined in the SEM, after rust removal. The ideal immersion time in the inhibited acid varied with the desired inspection. Although large fracture surface features remained visible after long cleaning times, fine features were damaged by even brief exposure to inhibited acid. However, inhibited acid cleaning is extremely helpful and remains the only means of obtaining useable fractographic results in many situations.