Two configurations of subsea blowout preventer (BOP) distributed control systems, which are triple modular redundancy (TMR) control system and double dual modular redundancy (DDMR) control system, are presented. With respect to common-cause failures, the performances of the two systems are evaluated by using Markov method with multiple error shock model. Due to the complexity, each system is split into three independent modules, and the corresponding Markov models are proposed subsequently. The probability of failure on demand, availability and reliability of the systems are evaluated by merging the independent Markov modules by Kronecker product approach. The results indicate that a same safety integrity level of SIL3 can be attained for the two configurations, which satisfies the requirement of subsea BOP control system, even though both of them have some advantages and shortcomings. In addition, for TMR control system, the effects of multiplicity distribution of multiple error shock and mean time to repair on reliability performances are studied.

An exploratory study on pressure vessel design procedures based on load and resistance factor design method for subsea blowout preventers subjected to external hydrostatic pressure is presented. Based on the procedures of working stress design method, the performance function of load and resistance factor design method is presented, and the design code is calibrated. The sensitivity analysis is done in order to investigate the effect of statistical characteristics of variables on the partial safety factors and design thickness of pressure vessel. The design procedures and results are compared with those of the traditional working stress design method. The results show that the load and resistance factor design method provides consistent reliability among the components of pressure vessel such as cylindrical shell and hemispherical head, and the method is less conservative than the working stress design method. Besides the conventional material of UNS S31603 stainless steel for subsea pressure vessel, UNS S31803 duplex stainless steel is also used, which could cause economic design results. Furthermore, the validity of the design results is confirmed by performing finite element model analysis by means of ANSYS software, which shows that the design thickness is secure enough when the pressure vessel works in 3000m ultra-deep seawater regions.

The galvanic corrosion behaviours of carbon fibre composite coupled to aluminium are studied when the galvanic couple is just immersed in artificial seawater or connected to a closed electric circuit. The effects of grinding condition, concentration of artificial seawater, applied torque, applied current and experimental time are studied. The roughness average, weight gain of carbon fibre composite and weight loss of aluminium are investigated as a function of the above variables. The results show that the applied current can accelerate the galvanic corrosion greatly. With improving grinding condition and increasing applied torque, the roughness average, weight gain of carbon fibre specimen and weight loss of aluminium specimen increase, reach maximum and then decrease. With increasing concentration of artificial seawater, applied current and experimental time, these measured values increase. Corroded surface morphology is also investigated using scanning electron microscopy.

A prototype of subsea solenoid valve for subsea blowout preventers is designed and manufactured. The deterministic and probabilistic thermal and electromagnetic finite element analyses are performed by using ANSYS software. The effects of uncertainties of five material properties, four physical dimensions and an applied voltage on the maximum temperature within the valve and the electromagnetic force with a given air gap are researched by means of Monte Carlo simulation (MCS) and response surface method (RSM). The thermal and electromagnetic experiments were done to validate the finite element analysis results. The results show that the radius of magnetic ring, applied voltage and thermal conductivity of 440C stainless steel have significant effects on the maximum temperature of subsea solenoid valve. The radius of plunger and inside radius of plunger sleeve have significant effects on the electromagnetic force of subsea solenoid valve. The results of finite element analysis and thermal and electromagnetic experiments indicate good matches. Therefore, the probabilistic finite element analysis shows its advantages in improving the development process and performance of subsea solenoid valves.