PSI - Issue 59

S.E. Donets et al. / Procedia Structural Integrity 59 (2024) 367–371 S.E. Donets et. alAuthor name / Structural Integrity Procedia 00 (2019) 000 – 000

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heterogeneities caused by the internals from the artefacts of measurement, thus cancelling potential of this approach as an early warning tool.

Fig. 3. A collage of line temperature profiles on the surface of pipe for different phases (heating ~ 436 s from the start of experiment, peak of heating (742 s), cooling (773 s)). Black-and-white image below - calculated fractal dimension map for the presented thermogram (773 s). In Fig. 3, a black-and-white fractal dimension D map was presented for the thermogram above. It appeared, changes in D can point out on the thermal heterogeneities. Fractal dimensions map is sensitive to changes in data values (e.g., Lam (2002)), incl. temperature distributions. In general, D had values around 2.0-2.15. D at ~ 2 attributes to the flat surface without any variations of intensity (temperature) or edges, meanwhile changes in intensity provoke deviations from D ~ 2 to higher values. If D -maps are homogeneous, with no areas of different values, then there are no statistically noticeable heterogeneities. However, in our case, we can see areas of variations which can be attributed to some local structural defects in the pipe. It was found, a contribution of lower-dimension of D values is higher at presence of heterogeneities, when temperature gradients are higher. Meanwhile it tends to higher values of D at smaller temperature gradients which is explained by edge detection properties of the Clar ke‟s fractal calculation method. It is worth pointing, fractal dimension mapping is not a primary metric because D is calculated based on some reference array of data. Thus, it can be considered as a supplementary tool for analysis for pollutant identification.

Fig. 4. Left – optical microscopy image of a pitting cavity in the inner wall surface. Right – H 50 microhardness tested in the vicinity of a pitting cavity near (red) and into the bulk (blue).