Role of oxide notching and degraded alloy microstructure in remarkably premature failure of steam generator tubes

The dynamic creep rupture of a secondary superheater tube in a 43MW coal-fired boiler by the decarburization and multilayer oxide scale buildup on both sides

“…With service hour extension, the hematite quantity increased up to 30%. In other case, EDS analysis indicated that the scale was mainly wustite (FeO) [16]. In addition to iron oxide type scales, other type scales had also been reported, such as the 'silica-type' (SiO 2 ) scale with other oxides (CaO, Fe 2 O 3 , Al 2 O 3 , MgO) [4], and the sodium aluminium silicates scale [14].…”

“…It was reported that the outer scale was mainly hematite (Fe 2 O 3 ) whereas the inner scale was wustite (FeO) [16]. XRD analysis results indicated that the scale was mainly hematite (Fe 2 O 3 ) [11].…”

“…At the burst location, the scale thicknesses on the steam-side were reported to be rather thin, such as 190 µm [16], 197 µm [2], 200 µm [8], and 240 µm [10]. As the scale thickness is exponential to the temperatures [6,16], the overheating temperatures mainly govern the scale thickness.…”

“…As the scale thickness is exponential to the temperatures [6,16], the overheating temperatures mainly govern the scale thickness. Therefore, in severe overheating, a thick scale would appear.…”

“…The classic methodology applied the Larson-Miller Parameter (LMP) to analysis the tube life [5][6][7][8]. In recent studies, researches focused on the aspects of metallurgical and oxide scales [9][10][11][12][13][14][15][16][17][18][19][20][21].…”