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© 2012 by Proceq SA
4.10 Evaluation
Typically, two criteria must be considered for the evaluation. (This is merely a guideline. The actual
evaluation should be carried out by a corrosion engineer.)
1.
Active corrosion can be expected at locations where a negative potential is surrounded by
increasingly positive potentials, i.e. locations with a positive potential gradient. Potential dif-
ferences with delta of 100mV within a 1m measurement area, together with negative
potentials are a clear indication of active corrosion.
2.
In order to plan corrective maintenance it is necessary to draw a border between areas of
active corrosion (anodes) and passive areas (cathodes) within the surfaces showing potential
gradients. In order to do this it is necessary to set a threshold potential that defines the inter-
section between the two states. ProVista has functionality which aids in this. (Read section 6
for details).
4.10.1 Example of a typical distribution
If the surface under test has both actively corroding as well as passive rebars, then the two states
exhibit differing statistical distributions of the potential. In the graphical representations provided
by ProVista there are typically three characteristic sections (Fig. 4.2). A flattening out of the section
shows that in these value ranges, there is less data available, i.e. the boundaries of the distribution
are here.
Fig. 4.2 Example of a relative frequency chart and cumulative frequency chart.
The potential ranges of active corrosion and passivity overlap.
The red cursor (leftmost) = minimum of the passive distribution.
The yellow cursor (rightmost) = maximum of the active distribution.
Active corrosion is practically certain in the region of the left hand (more negative) straight section.
Once these cursor lines have been set, the surfaces in this potential range will be automatically
displayed in the corresponding colour in the CANIN ProVista “Chipping Plot”.
In the example the red cursor line marks this threshold. A typical “Chipping Plot” taken from a practi-
cal example is shown below.
