2. Methods and materials

#### 2.1 The modified hyperbolic sine law for minimum creep strain rate and stress law

Xu's modified hyperbolic sine law is given as [12]:

$$
\dot{\varepsilon}\_{\min} = A \sinh(B\sigma^q) \tag{4}
$$

It was originally proposed by the first author for low Cr alloy [12], and its application was very successful [12].

Other existing and commonly used laws for high Cr P91 are listed Table 2; their suitability was examined first prior to the adoption of Xu's modified law.

The specific material used here is P91 (9Cr-1Mo-V-Nb). The experimental data of the minimum creep strain rate over a range of stress levels was taken from the published creep data [20] produced by the National Institute for Materials Science (NIMS), Japan.


Table 2.

The list of creep laws for the minimum creep strain rate and stress.

Modeling of Creep Deformation and Creep Fracture DOI: http://dx.doi.org/10.5772/intechopen.89009

## 2.2 Creep cavity fracture model
