Hazard identification methods are important tools to verify that the system is able to operate according to specifications under different operating conditions. Unfortunately, many of the traditional methods are not adequate to capture possible dysfunctional behavior of complex systems that involve highly coupled parts, non-linear interactions and software-intensive functionalities. The rather recent method named system-theoretic process analysis (STPA) is one promising candidate to improve the coverage of hazard identification in complex and software-intensive system. Still, there is no guideline for utilizing system-theoretic process analysis output to evaluate the potential of loss, which is important for basis of decision-making about system configuration and equipment selection. The focus of this article is to place an interface between system-theoretic process analysis and reliability, availability and maintainability (RAM) analysis. The approach named STPA-RAM model is proposed to translate feedback control loops into stochastic Petri nets for discrete event simulation. The proposed approach is demonstrated with a simple case related to subsea design concept. The major conclusion is that STPA-RAM model extends the application of system-theoretic process analysis, while also improving and as such reducing completeness uncertainty and model uncertainty, associated with input data and information for reliability, availability and maintainability analysis.

Framing reliability, availability and maintainability (RAM) aspects are critical for an engineering design, as RAM is concerned with the sustained capability of a system throughout its useful life.RAM analysts are responsible to consider both functional and dysfunctional behavior of a given system beyond the perspective of system designer. However, the system concept baseline developed by RAM toolset is often a partial view, which is either too abstract when preparing RAM analysis or too overloaded when integrating RAM analysis with design process. Such practice may not give systemic insights of the design concept, considering specific subsea design challenges such as limited accessibility and requirement for automate control. For this reason, it is of great importance to ensure an effective and sufficient communication between the domain of design and domain of RAM. Integrating with a well-known engineering discipline, such as systems engineering (SE), may help analysts to create the collaborative design environment necessary to control the design risks for a system with high complexity. This article proposes a new framework that links SE with RAM engineering by connecting relevant concepts and models used. A novel subsea design concept is offered as a case study to demonstrate the key changes in subsea design activities for addressing RAM with the proposed framework.