Subsea production systems (SPSs) have dominated the exploration of oil and gas resources in deep water; however, failure of SPSs can lead to enormous economic loss, serious environmental pollution and even severe casualties. Hence, the safety and reliability of SPSs have become a major concern. To guarantee the high integrity of SPSs, investment should be made in inspection and monitoring of SPSs (IMSPSs) in order to prevent failures of the subsea equipment, as much as possible. This paper reviews the current progress in technologies for IMSPSs using non-destructive testing (NDT). The basic principles and features of four common NDT techniques used for IMSPSs are reviewed. Based on these NDT techniques, the current development of IMSPSs, as well as the latest advanced technologies, is then discussed. Furthermore, capabilities and limitations of IMSPSs are discussed. Finally, suggestions for future development of IMSPSs are provided.

Elbows are a vulnerable part of piping systems in erosive environments. Traditionally, plugged tees are used instead of elbows when the erosion rate is high. However, the advantage of plugged tees over elbows in large-scale pipelines is unclear. A comprehensive computational fluid dynamics study was carried out to predict the erosion rate in plugged tees and elbows. A numerical method was first used for aluminium elbows and tees with available experimental data through which the accuracy of the numerical solution was verified. After validating the model, numerical modelling was used to compare the erosion rates of plugged tees and elbows in varying geometrical conditions, ranging from 0.0254 to 0.6 m diameter carbon steel pipes transmitting multiphase gas/sand flow. The effects of internal flow velocity and sand particle size on erosion rates were also investigated. The numerical results revealed that the erosion ratio between plugged tees and elbows strongly depends on the internal diameter of the pipe, the flow velocity and particle size. Hence, the influence of these parameters should be considered for proper selection of the fittings to be used. Finally, numerical modelling of erosion in two subsea jumpers outfitted with standard elbows and plugged tees was presented.

Hydrogen is widely regarded as a key element of prospective energy solutions for alleviating environmental emission problems. However, hydrogen is classified as a high-risk gas because of its wide explosive range, high overpressure, low ignition energy, and fast flame propagation speed compared with those of hydrocarbon-based gases. In addition, deflagration can develop into detonation in ventilation or explosion guide tunnels if explosion overpressure occurs, leading to the explosion of all combustible gases. However, quantitative evidence of an increase in the explosion overpressure of ventilation tunnels is unavailable because the explosive characteristics of hydrogen gas are insufficiently understood. Therefore, this study investigated an explosion chamber with the shape of a ventilation pipe in a ship compartment. The effect of tunnel length on explosion overpressure was examined experimentally. For quantitative verification, the size of the hydrogen gas explosion overpressure was analyzed and compared with experimental values of hydrocarbon-based combustible gases (butane and LPG (propane 98%)). The experimental database can be used for explosion risk analyses of ships when designing ventilation holes and piping systems and developing new safety guidelines for hydrogen carriers and hydrogen-fueled ships.

Collisions frequently occur at sea, leading to serious human injury, and damage to property and the environment. Furthermore, the increasing number of offshore platforms means that collisions between vessels and offshore structures are a frequent type of accident. Platforms are at a greater risk of collisions than ships, because they have no avoidance capability when operating. Recently, the expansion of offshore wind farms in response to new green energy requirements has led to wind-turbine installation vessels (WTIVs) being in common use. WTIVs are similar to fixed jack-up rigs, and they are self-propelled because they must be able to quickly relocate during wind-farm operation. Therefore, it is important to consider the operational characteristics of WTIVs when calculating their collision risks. This study develops a new method for analysing WTIV collision frequency and then compares the proposed method with the existing methods. It also discusses the implications of the methods for ship-WTIV collision-frequency analysis.