Effect of oxidation on creep behaviour

The formation of thick oxide scales has several consequences for the service behaviour of components  

11 Rupture life reduction for two P92 components, a pipe of 300 mm diameter and wall thickness 40 mm and a tube of 40 mm diameter, wall thickness 6 mm. 

The thermal insulation effect of a thick oxide scale which reduces the heat transfer across the component wall can lead to overheating. A small increase in component operating temperature will reduce the stress rupture life considerably, as shown in Fig. 11.12. A relatively thin oxide scale leads to a dramatic reduction in rupture life due to the increase in temperature. 

If the oxides spall during service, there is the danger of tube blockage as the spalled oxide accumulates inside the tubes, resulting again in overheating. If oxide particles are carried with the steam into the turbine, erosion of the blades may occur. 

The matrix becomes depleted in those elements that are selectively oxidised to form the thick oxide scales, leading to microstructural changes and associated potential effects on the long-term strength. This effect has been investigated in this work for AUoy 800 and P92. 

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