Analysis of an All-Electric Safety Subsea Actuation System Architecture

Abstract

The paper compares a state of the art electro-hydraulic actuation system with a novel all-electric actuation system for subsea x-mas trees. For this purpose, the two systems are compared to each other based on the same method. The capability of providing the safety is analyzed based on the functional safety standard for electrical, electronic programmable devices. The architectures of both designs are presented. The components of each system are described in detail and the data used for the safety analysis are provided. Based on the failure rates for each component the probability of failure on demand is calculated and discussed. The resulting probability of failure on demand (PFD) is analyzed regarding the shares of the total PFD. The resulting safety integrity levels (SIL) of both systems are determined. The electric system provides by factor two lower PFD compared to the hydraulic system. Each component is allocated to the component type and to the Safe Failure Fraction (SFF) based on the Hardware Fault Tolerance (HFT). The conclusion shows the significant difference in the diagnostic coverage of both systems.