## 3 Life Evaluation for High-Temperature Steam Pipes
### Lifetime Prediction  
To calculate the lifetime of plant facilities, basic data such as operating conditions and hours or number of cycles are essential. Because a lifetime is related to the dominant damage mechanism and damage model, various data are used to calculate the life consumption rate. In the case of the Manjung power plant, creep damage is more dominant than LCF because the operation has been running for a long time (i.e., 88,311 operating hours) and the number of cycles (i.e., 50 cold, 23 warm, 66 hot) is too small. The material subjected to a high-temperature greater than 0.4 to 0.5 of the melting temperature will slowly deform under loads that would not cause any plastic deformation at room temperature. Creep stresses at this temperature are expressed by a typical result of creep tests and extrapolation of data for the long-time creep phenomenon. The strain not only depends on the stress, but also depends on temperature and time.  
The creep life consumption rate was evaluated by the stress-based life prediction methods such as TRD, allowable stress, and 3 DDMS. In addition, the LCF life consumption rate was calculated by both methods (NCC and RCC). The creep and LCF life consumption rates were chosen to be the maximum value of each method. The total life consumption rate was estimated using Equation (8). The total life consumption rates of different locations are presented in Table 8. For the MSP with straight type, most of the maximum creep life consumption rate was estimated by the TRD method, based on the theoretical equation using geometric information. However, the creep life consumption rate calculated by the 3 DDMS method had a maximum value at position 1. The 3 DDMS method determined the stress according to the displacement because the displacement at location 1 was the largest compared to locations 7 and 8, which were constrained adjacent to the turbine.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Location**} & \multicolumn{2}{c}{**Creep Life Consumption Rate (\%)**} & \multicolumn{2}{c}{**LCF Life Consumption Rate (\%)**} & \multicolumn{2}{c}{**Total Life**} \\ \cline{2-7}  & **3 DDMS** & **TRD** & **Allowable** & **Rainflow Cycle** & **Number of Cycles** & **Range(\%)** \\ \hline
**1** & 23.5 & & 8.3 & \(3.34\times 10^{-9}\) & 5.82 \(\times 10^{-8}\) & 23.5 \\
2 & 9.9 & & 8.1 & \(3.82\times 10^{-10}\) & 5.82 \(\times 10^{-8}\) & 10.24 \\
3 & 1.39 & & 7.32 & \(3.18\times 10^{-18}\) & 5.82 \(\times 10^{-8}\) & 10.24 \\
4 & 1.05 & & 7.51 & \(6.49\times 10^{-20}\) & 5.82 \(\times 10^{-8}\) & 10.24 \\
5 & 3.53 & & 8.3 & \(3.09\times 10^{-19}\) & 5.82 \(\times 10^{-8}\) & 10.24 \\
6 & 2.99 & & 8.1 & 0 & \(5.82\times 10^{-8}\) & 10.24 \\
7 & 1.4 & & 8.3 & \(2.09\times 10^{-14}\) & 5.82 \(\times 10^{-8}\) & 10.24 \\
8 & 0.17 & & 7.7 & \(7.74\times 10^{-16}\) & 5.82 \(\times 10^{-8}\) & 10.24 \\ \hline H-joint & 36.62 & 12.99 & 8.71 & 0.1 & \(5.82\times 10^{-8}\) & 36.62 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Results of life consumption rate with different locations of the main steam pipe by considering the total operating hours.  
For the LCF life prediction, both the rainf cycle and the number of cycles showed a lower value of life consumption rate, which was compared with the creep life consumption rate. It was noted that the creep was a more dominant factor of life prediction than low cycle fatigue because the operating hours were relatively longer than the number of cycles. In the case of MSP with the H-joint type, the total life consumption rate where the creep life consumption rate was the dominant factor showed a relatively higher value. From the stress analysis, the maximum stress of MSP was observed at the curved edge of the H-joint, due to the role of stress concentration of the curved edge. Thus, the pipe system that was subjected to high temperatures was easily exposed to creep damage, and especially, creep damage accumulated more at the curved edge.