Larson-Miller relation

Blade life eomparison is provided in the form of the stress required for rupture as a funetion of a parameter that relates time and temperature (the Larson-Miller Parameter). The Larson-Miller parameter is a funetion of... 

From the Larson-Miller analysis, it is possible to derive more easily interpreted information relating to the effects of sustained high temperature on the life of a tube. A common rule of thumb is that a tube wall temperature increase of 20°C will shorten a tube life by over 50% from its design period of 10 years to less than 5 years. The cost of a typical reformer tube is USD 6000-7000. With typical reformer sizes in the order of 300-400 tubes and taking on-site expenditure into account, this puts the cost of a complete re-tube in the range... 

Comparable tedmiques developed for metal creep are, due to Dom, the temperature-oompeiisated tune parameter, and the related Larson-Miller parameter. 

The Larson-Miller method is applicable to a variety of materials, including ceramics, and is most commonly used because of its simplicity. This relation is given as ... 

P = T(C -I- Intf) is the Larson-Miller parameter [henceforth LMP] and is f(activation energy is independent of applied stress, this equation may be used to relate the difference in rupture life to differences in temperature for a given stress. In many cases, C is indeed 20, which is obtained from the intercept with the logt axis of a logt, versus 1/T plott (Fig. 6.111). The slope of such a plot, namely Q/k (=P), is a function of stress, as seen in the schematic Fig. 6.111. For a graphic presentation, Eq. (6.102) may be written as ... 

The Larson-Miller parameter, P, in Eq. (6.102), is one of the useful parameters used for predicting creep life in metallic materials, but it is useful for ceramics as well. The LMP may be used to describe the stress-temperature-life relation in a SiC/SiC composite by means of the following expression ... 

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