## 4 Case Study
### Failure Modes and Effects Analysis  
The FMEA of the systems and subsystems of the LNG plant has been prepared in order to compile historical data on failures in each of the plant's system components and subsystems. This aims at defining the criticalities that allow, subsequently, to move forward  
Figure 5: General flowsheet of the plant. with the study. It should be noted that this text does not provide historical details, dates, or frequency of failure or repair times. On the other hand, and in order to simplify the study and its description, average values of MTBF and MTTR of each component are provided. **Critical Process Failure Modes and Critical Equipment Selection**  
For the purposes of this study, critical equipment are those components whose failures or stoppages could cause or contribute to a decrease in the reliability and availability of the main production line. Among these failure modes and given that certain components have MTBFs that are too long, causing a minimal impact on the RAM analysis, some of them were not considered in this study. Table 1 shows the equipment selected and defined as critical. **Analysis of Vaporization and Pumping Zone Plans**  
The technical information of the vaporization and pumping zones was analyzed in order to obtain a detailed representation of the process-flow diagram of the plant under study, providing the possibility of constructing the Reliability Block Diagram, as follows. **Elaboration of Reliability Block Diagram (RBD)**  
The data obtained from the FMEA, the existing maintenance plans of the pumping and vaporization zones, and the selection of critical equipment within the system with its most frequent failure mode (previous stages) have been taken into consideration for the elaboration of the RBD. Figure 6 shows the RBD diagram of the pumping and vaporization plant. **System Reliability, Maintainability, and Availability Calculation Procedure**  
To make all this representation and the calculations necessary to carry out the RAM analysis feasible, a spreadsheet-based calculation platform was developed (supported by specific macros), which constitutes the materiality of the methodology proposed in this work. The procedure adopted and the work it was based on [23] is summarized below. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Equip.** & **Tag** & **Systemic Load** & **Failure Mode** & **MTBF (Years)** & **MTTR (h)** \\ \hline Open Vaporizer ORV & 300-E-102 A/B/C & \(3\times 33\%\) & Short Repair & 0.5 & 8 \\ Closed Vaporizer SCV & 300-E-103 & \(1\times 33\%\) & Short Repair & 0.5 & 10 \\ HP Pumps & 300-P-102 & \(5\times 33\%\) & Short Repair & 1 & 28 \\ SW Pumps & 400-P-101 A/B/C/D/E & \(4\times 33\%\) & Spurious Failure & 2.5 & 4 \\ Pipeline Emergency Valves & XZV-03018/3026 & \(2\times 100\%\) & Short Repair & 4 & 4 \\ Gas Measurement Package & 300-X-104 A/B/C & \(3\times 50\%\) & Gas Leak at Flange & 5 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Selection of critical failure modes of the process. Figure 6: Configuration (RBD) of the system under analysis. Once the reliability function R(t) has been obtained for each of the 18 pieces of equipment that make up the system, the reliability of the existing subsystems is calculated.