A System to Rapidly Characterize Pitting Corrosion on Metallic Surfaces
Southwest Research Institute (SwRI) developed a system that, disregarding surface roughness and topographic features, efficiently characterizes pitting corrosion on metallic surfaces, yielding information such as:
- Pit counts
- Pit depth profiles
- Distributions of pit depths
- Areas affected by pitting corrosion
The system consists of a laser profilometer, or other device for measuring the surface profile of the metallic coupons, and a method for analyzing the resulting data using a pattern recognition algorithm. The system is appropriate for laboratory-scale coupons ranging in dimensions up to a few centimeters on each side. The system is useful in efficiently characterizing pitting corrosion in accelerated experiments.
Examples of graphic displays and information extracted from profilometry data. The micrograph is provided to demonstrate the adequacy of the pattern recognition algorithm.
The technology is applied by profiling a coupon surface using a laser profilometer or similar technique and then analyzing the output data using a specialized pattern recognition algorithm. The algorithm is predominantly a data filtration method that removes spurious spikes in the output data associated to surface roughness and shallow topographic features. Isolated spikes in the surface profile data are mostly related to surface roughness, while grouped spikes indicate pitting corrosion. The algorithm works by mapping the grouped spikes into a 2-dimensional array. This provides a view of the coupon surface indicating the position of pits, while ignoring surface roughness and other shallow features. Once output data associated with pitting corrosion are isolated, additional information can be extracted including but not limited to the number of pits, distributions of pit depths, separation of deep pits from shallow pits and topographic features, and the area affected by pitting corrosion.
SwRI tested the system on 304 stainless steel (SS) coupons that experienced pitting corrosion. The pitting corrosion features were characterized using a laser profilometer and the pattern recognition algorithm. The figure above includes an example of a density plot (4 cm × 4 cm surface), filtered clusters associated with pits, and the deepest pit identified by the system. Once the location of a specific pit is defined, it is possible to "zoom-in" to present additional displays such as 3-dimensional pit surface or contour plots. The figure provides a micrograph to demonstrate the adequacy of the technique to characterize pitting corrosion. This technology has been tested on numerous coupons with different pitting corrosion features.
characterization of pitting corrosion • metallic surfaces • pit counts • pit depth profiles • pitting corrosion on metallic surfaces • pipe density