The steamside oxide formed on two TP347H superheater tubes was compared. The two specimens investigated were exposed in situ in power plants in Denmark, one specimen was coarse-grained and the other was fine-grained. Parts of both the coarse-grained and the fine-grained specimens were turned (machined on the inner side) to give a constant metal thickness so more precise wall thickness measurements could be undertaken. Machined and non-machined areas were investigated using light optical microscopy, and scanning electron microscopy with EDS analysis. The oxide on the fine-grained specimen was also investigated with grazing incidence X-ray diffraction. Results from coarse-grained and fine-grained specimens (machined and non-machined) show that grain size influenced oxide thickness and morphology. The oxides from non-machined specimens has an outer iron rich oxide and an inner iron chromium oxide. However a thinner oxide had grown on the fine-grained steel. The machining of fine-grained and coarse-grained specimens resulted in a thin chromium rich oxide layer. The presence of surface deformation of the inner metal surface was evident on the coarse-grained specimen but not on the fine-grained specimen. However other indications that the fine-grained specimen had been deformed were observed. The influence of temperature, grain size, surface finish and exposure duration is discussed.
|Journal||Materials Science Forum|
|Publication status||Published - 2004|