# Reliability and Risk Centered Maintenance: A Novel Method for Supporting Maintenance Management
## 4 Case Study
\[\text{FFI}=\text{max}\ (\text{EnI},\text{PFI},\text{PGAI}) \tag{1}\]  
For better comprehension, Tables 3-5 show the classification of each impact type (namely, EnI, PFI, and PGAI) resulting from functional failures. Additionally, Table 6 presents the criteria for classifying the FMP in the context of this specific case study. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline
**Item** & **Functions** & **Functional Failures** & **Functional Failure Effects** & **EnI** & **PFI** & **PGAI** & **FFI** & **Failure Mode ID** & **Failure Mode** & **FMP** & **FMRL** \\ \hline \multirow{8}{*}{ \begin{tabular}{c} 21. Water \\ intake gates \\ \end{tabular}  } & \multirow{8}{*}{ \begin{tabular}{c} Low water intake \\ when the generating \\ unit is in operation \\ \end{tabular}  } & \multirow{8}{*}{ \begin{tabular}{c} Low airlow the water \\ intake to flow \\ \end{tabular}  } & \multirow{8}{*}{ \begin{tabular}{c} Low airlow the water \\ through the turbine \\ \end{tabular}  } & \multirow{8}{*}{\ \begin{tabular}{c} Water does not flow \\ through the turbine \\ \end{tabular}  } & \multirow{8}{*}{
\begin{tabular}{c} 1  
As can be noticed in Table 7, each functional failure may have one or more failure modes associated with it. However, the assessment of the impact of a functional failure is not dependent on them. In other words, each Functional Failure Impact (FFI) is associated with the consequences estimated when the functional failure occurs. On the other hand, as different failure modes have different probabilities of occurrence, they are directly associated with the FMP. After establishing FMRLs for all defined failure modes, the subsequent steps 7 and 8 of the RRCM were executed. From the risk classification obtained, it is possible to determine the appropriate failure mode management policy and then the maintenance tasks to compose the maintenance plans. The definition of failure mode management policies follows the decision diagrams for each risk level presented in Figures 3-7 as well as the guidelines for verifying the applicability, technical feasibility, and effectiveness of a maintenance task presented in Figure 8. The results obtained for the failure modes listed in Table 7 are presented in Table 8.  
To enhance the understanding of the proposed method and its practical implementation, the reasoning utilized to determine the maintenance management policy for failure mode FM.6.7.G, cracks in the bearing housing, are provided. Firstly, the FFI score assigned to the functional failure associated with this particular failure mode (FFI = 4) is mainly related to its impact on the environment. If the turbine guide bearing housing loses its function of restricting the lubricating oil to the inside of the bearing, in this case, due to the development of cracks in the bearing housing, oil leaks may occur. In milder cases, the main consequence is the accumulation of oil puddles in the plant's facilities. However, due to the position of the turbine guide bearing in the generating unit and its proximity to the water flow, in some cases, the oil may not accumulate in the installations and leak directly into the river, which becomes a serious environmental problem. On the other hand, the probability of the development of cracks in the bearing housing of the generating units of the plant considered is very low, with no case being reported in its almost five decades of operation. In this way, the score associated with FMP is the lowest possible value (FMP = 1). Consequently, from the FFI and FMP scores, the risk level associated with the failure mode is medium. From the medium FMRL diagram (Figure 5), the initial question to address is if there is an on-condition task that is applicable, effective, and technically feasible to be performed. In this instance, it would not be possible to continuously monitor the development of cracks in the bearing housing, resulting in a negative response to the first question.