## 3 Proposed Methodology
### FMEA Steps  
Aside from typical FMEA steps that are detailed and explained in reference [11], the additional tasks that should be implemented at this stage include revising traditional RPN values and ranking components based on the weighted RPNs. Experts brainstorm and report the results as in the traditional FMEA process. In this case, the minimal cut sets that were obtained from the fault trees aid the failure mode identification process. The weights are multiplied with RPNs obtained from the traditional FMEA procedure. It must be noted that minimal cut sets may include one or more components which should be assigned relative importance, as multiple failures are not considered. Components with highest RPNs may not necessarily possess highest WRPNs in this methodology, hence added criteria for ranking. An integrated FTA-FMEA worksheet carrying all necessary data from the traditional FTA and FMEA approaches is shown in Table 2, ending with suggested preventive actions. The traditional approaches of both FTA and FMEA techniques are revisited though all relevant software advances. This is to provide the basis for criteria amelioration at every stage. Certain assumptions are considered with this methodology:  
* Failure modes in FMEA are a direct result of the faults identified in the FTA process and the failure causes are assumed to be mutually independent. * In the FMEA method, only the most critical failure modes are considered. Double or multiple failure modes inclusion, though representing a major improvement to traditional FMEA, would be important only when the assessment's aim is beyond the scope of this work such as risk identification and further quantitative analysis. * The complex system under consideration should be coherent and modular with each module relevant to system functioning, with the FTA possessing only _AND_ and _OR_ gates. In the next section, a case study is presented to illustrate the application of the proposed model in an industrial context. minimal cut sets and minimal path sets of common-cause failure (CCF). This is particularly important for BOP systems, as in an assembly with parallel connections, wherein CCF is a major characteristic [24]. FTA has been so far employed in several BOP reliability analyses (see, e.g., references [25; 26; 27; 28]), proving to be convenient for identifying failure modes within the BOP stack. [PERSON] and [PERSON] [29] used both FTA and FMEA for reliability analysis of the device and its hydraulic control system. They employed the inductive bottom-up approach to determine consequences of part malfunction and to link undesired events to their causes, the deductive supplement. FMEA was again extended to include criticality and applied to the entire system in a study conducted by American Bureau of Shipping (ABS) and ABSG Consulting Inc. for the Bureau of Safety and Environmental Enforcement (BSEE) [30]. A BOP reliability analysis model was recently developed by employing the software package Norsys Netica ([[https://www.norsys.com/netica.html](https://www.norsys.com/netica.html)]([https://www.norsys.com/netica.html](https://www.norsys.com/netica.html))) to aid in identification, evaluation, and prioritization of failure risks [31]. For complex systems such as BOP in which interdependencies between sub-components are complicated, combined (hybrid) techniques are worthwhile. Identifying critical components in a system with over seven (7) main subsystems, housing about 600 individual components may be the starting point for more detailed qualitative and quantitative analyses. The proposed integration methodology is explained step by step as follows:  
1. Reliability goal and system boundary definition - Identification of critical components within the system: As a large specialized and mechanical valve assembly that is used to seal wells against kicks or blowouts during drilling or work-over operations, a critical component will be the one whose failure will lead to the failure of the entire system or a major part of it.