Correlation of Process Data and Electrochemical Noise to Assess Kraft Digester Corrosion: Kamloops Experiment Page: 95 of 108
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
The data of Table 10 suggest several important trends. First, the corrosion rate of the
probes determined from the dimensional change during the experiment is consistent qualitatively
(ranking of corrosion rates among locations) and quantitatively (specific corrosion rate at each
location) with the historical corrosion rates in the vessel., More importantly, because operational
conditions vary with time, the probe corrosion rates calculated from dimensional changes are also
consistent with the vessel corrosion rates calculated from the most recent changes in wall
thickness values.
Within some predictable limitations, the integrated current sums also predict corrosion
rates consistent with wall thickness measurements., The corrosion rates so calculated are initially
relatively high, but the corrosion rate for freshly exposed steel (no mill scale or corrosion product
accumulation) should be expected to be somewhat higher in the initial stages of exposure
compared to later stages. It is significant to note that the digester shell also experienced higher
rates of corrosion in the initial periods of operation (first few months after start-up) than those
currently experienced, as much of the "pitting" and "oceans-and-islands" patterns of corrosion
developed between the initial start-up of the vessel and the first visual inspection.
As corrosion products accumulate on the electrodes with extended exposure time, the
corrosion rates calculated from the integrated current sums for each probe tend to decrease.
These values are consistent with both the current corrosion rate estimates from UT measurements
for the vessel and the historical ranking of corrosion rates from UT measurements at these
locations. Recall that, generally speaking, the integrated current sums should underestimate the
total corrosion from each probe because the current sums account for only the current that passes
through the ZRA between electrodes, and that any contributions of self-terminating current
(anodes and cathodes near each other on the same electrode rather than on different electrodes)
are not counted toward the total. Further, as corrosion products tend to accumulate and increase
the resistance between electrodes, the statistical likelihood of anodes and cathodes near to each
other on the same electrode surface increases, so the integrated current sums might be expected to
decrease with extended exposure.
The primary conclusion to be drawn from Table 10 is that the ECN probes generate
corrosion rates that are consistent with wall thickness changes at nearby locations of the digester
shell. That they do not agree precisely with wall thickness measurements is of no practical77
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Pawel, SJ. Correlation of Process Data and Electrochemical Noise to Assess Kraft Digester Corrosion: Kamloops Experiment, report, May 9, 2002; United States. (https://digital.library.unt.edu/ark:/67531/metadc737191/m1/95/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.