To date, a particle counter or monitor has traditionally been used to detect the transfer of corrosion products in a power generation steam cycle. While this method has been generally well accepted and documented, particle counters do not have a standardized method of calibration and usually need to be calibrated at each facility. Where multiple measurement points are desired, it can also become rather costly. The technology is also limited to detecting particles with a size of 2 microns or greater.
Quantifying the amount of iron in the water on site has also been challenging in the ultra low range. Colorimetric methods that could be readily used at the plant were limited to 9 μg/L or greater. This has furthered added to the challenge of ascertaining whether significant corrosion product transfer was occurring at a particular point in the process.
Data has recently been gathered to determine whether corrosion product transfer in the steam cycle could be detected using a laser nephelometer. The added benefit of this methodology is the ability to detect particles in the sub-micron size range. Preliminary results have been very encouraging.
To further support these results, a modified trace level iron test has been documented using colorimetric methods and a lab spectrophotometer. Finally, a correlation has been made between these two methods, offering the opportunity of using a continuous measurement to determine iron concentrations to 1 μg/L or lower. The data can be further related to plant load and cycle pH in order to shed further light on how these parameters influence flow accelerated corrosion.
