## 3 Case Study Analysis
### Case Study 4: Safety Barrier System  
This case study is about a safety barrier system (emergency shutdown valve) that has annual functional tests (full stroke). This valve is part of the safety instrumented system that functions on demand to stop the flow of a hazardous fluid upon the detection of a dangerous event. It is assessed based on the safety integrity level (SIL) requirements that quantify the reliability of safety-related systems and their ability to perform their intended safety functions. The safety regulations recommend annual full stroke functional testing in which the closing and opening time is measured and compared to acceptable levels to ensure valve technical condition. However, in a couple of valves it was observed that the annual closing time was normal for a couple of years until an increase in the closing time was observed (it was close to the unacceptable level); however, in the year after, the closing time was reduced and it looked like the technical condition was getting better. One year later, the closing time had increased to an unacceptable level and had been registered as failure. The expert tried to explain this phenomenon on the basis of the flashing action of the valve. When the valve is closing, the surfaces are cleaned due to friction, but also scratched. Furthermore, the full stroking tests are heavy tests that the technical manager and other practitioners believe to have an impact on the technical condition. In this sense, more frequent but lighter tests such as partial stroke testing shall be recommended. However, the main risk related to partial stroke testing has a lower diagnostic coverage of hidden failure modes compared to full stroke testing. Therefore, the case company intends to install a valve monitoring system to ensure that the valve would function as intended in the next needed time. In addition, the company planned to revise the document \"maintenance and testing concept\", which will be used to define maintenance engineering requirements for new valves in the future. Several emerging practices have been observed in this case, summarized in Table 6. The first emerging practice is a new worksheet to determine the diagnostic coverage of valve monitoring systems and compare it with functional testing. The second emerging practice is the guideline on how to perform or execute the functional test using the valve monitoring system. The third emerging practice is a new visualization to track valve performance in all events (for operations or testing purposes). \begin{table}
\begin{tabular}{l l} \hline \hline
**No.** & **Emerging Practice** \\ \hline
1 & New worksheet to determine diagnostic coverage of the valve monitoring system \\
2 & New guideline to execute the functional testing using the valve monitoring system \\
3 & New visualization to track the valve performance over all events (for operations or testing purposes) \\
4 & New guideline to build model-based maintenance and test concept \\
5 & New guideline to continuously manage and coordinate the interactions between documents and models \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary of emerging practices in case study 4. \begin{table}
\begin{tabular}{l l} \hline \hline
**No.** & **Emerging Practice** \\ \hline
1 & New worksheet to determine the maintenance concept and best available technology \\
2 & New visualizations of the master data \\
3 & New guideline to explore the capability to depend on fixed maintenance intervals \\  & and planned visits \\
4 & New model to estimate the plug&play maintainability \\
5 & New worksheet to determine diagnostic coverage of CUI sensors \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of emerging practices in case study 3. The previous visualization is based only on functional testing events; however, with a 24/7 valve monitoring system, any closing and opening events are registered.