Exfoliation & Lamellar Corrosion
During Inspection
Severe leakages in a steam generator superheater were the leading cause of a major outage a few months after first operation of a power plant. In the course of a visual inspection, the first section of the superheater was observed to develop several sharp perforations, impingement and general abrasion on the baffle/tube interface.
Heavy deposits were also found all over the steam drum along with serious surface exfoliation.
Conclusions
Failure investigation was conducted to reveal that unsatisfactory chemical cleaning left a heterogeneous layer of calcium carbonate, sodium phosphate, silica and iron citrate.
This layer inhibited the formation of a consistent magnetite layer that was partially developed across the surface.
As a result, scales detached from surface and passed to steam side leading to significant damage in the superheater and dramatic consequences to the project.
