FMECA of an unmanned system for subsea inspections and seabed surveys

Introduction and objectives of the FMECA of an unmanned system for subsea inspections

MAR Consulting performed a Failure Modes, Effects and Criticality Analysis (FMECA) of an unmanned system for subsea inspections and seabed surveys, as part of the technology qualification process. The main objectives of the FMECA were to:

  • Identify failure modes of the different sub-systems/components in the system with a technology readiness level (TRL) lower than 5;
  • Evaluate the criticality of each failure on the system;
  • Provide the basis for planning of the technology qualification activities;
  • Provide input for the testing program;
  • Provide input for the selection of components during subsequent stages of the project.

Methodology

An FMECA is an inductive (forward logic) single point of failure analysis based on IEC 60812, which helps to identify potential failure modes based on experience with similar products and processes or based on common physics of failure logic. Effects analysis refers to studying the consequences of those failures on different system levels. An FMECA is hence a systematic procedure for the analysis of a system to identify the potential failure modes, their causes, and effects on system performance (performance of the immediate assembly and the entire system or a process).

Considering the initial stage of the project, MAR Consulting used a top-level approach on the assembly/package level. To ensure a structured examination, the system was divided into its constituent assemblies/packages based on their functionality in the system. For each element, the assembly/package level FMECA consisted of the following steps:

  • Defined relevant elements;
  • For each element X:
    • Described main function(s);
    • Identified failure mode(s);
  • For each failure mode Y:
    • Tentatively identified detection method(s) and controls;
    • Identified the local failure effect;
    • Identified the failure effect at system level;
    • Tentatively identified possible causes for failure;
    • Defined criticality (severity and probability of occurrence);
    • Noted other remarks and/or recommendation for further action(s) (optional).

Conclusions

The unmanned system is comprised of an unmanned surface vehicle including a launch and recovery system for the autonomous underwater vehicle. The most critical sub-systems at that stage of the project were the satellite communication system, the unmanned surface vehicle main control hardware and software; and the guidance system.

The output of the analysis was a number of recommendations to steer the system design to meet its specifications at this early stage. A general recommendation was to include sub-systems suppliers in FMECAs and similar analysis as the project progresses.

MAR Consulting has extensive experience performing FMECAs of complex systems such as FMECA of topside BOP and control system · MAR Consulting; FMEA of electrical and control systems in subsea BOP · MAR Consulting; FMECA of redundant subsea BOP deadman-autoshear · MAR Consulting; FMECA electrical and control systems in subsea BOP · MAR Consulting; FMECA of blow-out preventer hydraulic system · MAR Consulting.

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