Proceedings of Topical Meeting on Optoinformatics (pdf-format, 1.21 ...

SAINT-PETERSBURG, October 17 – 20, 2005 61
PITTING CORROSION MONITORING WITH ELECTRONIC-
SPECKLE PHOTOGRAPHY
Frankevych L. F.
Karpenko Physico-Mechanical Institute <strong>of</strong> NAS <strong>of</strong> Ukraine, Lviv, Ukraine
The new method <strong>of</strong> spatial-temporal electronic speckle-photography was
proposed to research the pitting corrosion processes. The experimental setup
for realization this method was calculated and created. Appearance <strong>of</strong>
corrosion pitting was registered for a steel beam specimen.
Crevice corrosion and corrosion fatigue <strong>of</strong> construction materials belong to the most
dangerous types <strong>of</strong> corrosion-mechanical damages [1] . Pitting corrosion is an initial stage <strong>of</strong>
corrosion fatigue and reduces to destruction <strong>of</strong> materials. It is very difficult to expose
intercrystalline, transcrystalline or mixed type <strong>of</strong> crack by the existent methods <strong>of</strong> fault
detection. Therefore, the problem <strong>of</strong> development <strong>of</strong> the new methods for diagnostics <strong>of</strong>
corrosion fatigue on the initial stages is enough actual. Now there are some electronical
and optical methods for research <strong>of</strong> this type <strong>of</strong> corrosion-mechanical destruction.
However they are enough laborious and need a long time for researches and can’t use for
real – time monitoring.
To research the processes <strong>of</strong> pitting and corrosion ulcers nucleation, we have
proposed the hybrid optical-digital method <strong>of</strong> spatial-temporal electronic specklephotography
[2] , which is quite simple and does not yield other on the explored parameters.
For this purpose, the experimental setup for realization this method was calculated and
created. It contains the loading setting and spatial-temporal speckle-correlator. The studied
specimen is situated in a glass cuvette with a liquid. One end <strong>of</strong> a specimen is fixed to the
cantilever <strong>of</strong> the loading setting. The calculation <strong>of</strong> the spatial-temporal specklecorrelator’s
optical system was conducted, which provided the necessary scale <strong>of</strong> images
and sizes <strong>of</strong> speckle (the average size <strong>of</strong> speckle must be larger then pixel size). The optical
system was located on a holder, which is hardly fastened to immobile part <strong>of</strong> the loading
setting. Such fastening provides immobility <strong>of</strong> optics relatively to the studied specimen.
The experiments were conducted for steel 12H1MF <strong>of</strong> the pipeline systems <strong>of</strong> power
equipment, from which studied specimen were done with a smooth cut for localization <strong>of</strong>
the corrosion processes. The specimen was immersed into 3% water solution <strong>of</strong> NaCl with
additions <strong>of</strong> HCl and NaOH for achievement <strong>of</strong> value pH=6,5. And it was loading with
cyclic frequency <strong>of</strong> equal to 0,1 Hertz. To test the rectangular grating <strong>of</strong> cross-correlation
peaks obtained as a result <strong>of</strong> temporal changes <strong>of</strong> studied surface; at first we have produced
the rectangular grating <strong>of</strong> autocorrelation peaks by autocorrelation <strong>of</strong> the surface fragments
(subimages) <strong>of</strong> the explored area in initial condition. The next stage <strong>of</strong> experiments
consists in producing <strong>of</strong> gratings <strong>of</strong> cross-correlation peaks during fatigue loading <strong>of</strong> the
specimen. The reduction <strong>of</strong> intensity <strong>of</strong> cross-correlation peaks in relation to intensities <strong>of</strong>
autocorrelation peaks <strong>of</strong> the proper fragments carried information about the presence <strong>of</strong>
corrosive damages (pittings) on the studied specimen area. Appearance <strong>of</strong> corrosion ulcer
and its transformation in microcrack was registered.