Concrete coating is used to stabilize subsea steel pipelines against hydrodynamic forces. However, stiffness differences at field joints can cause strain concentration, which may affect the pipeline's integrity. Existing methods to assess strain concentration, including full-scale testing and finite element modeling with solid elements, provide accurate results but are often costly and slow. This study presents a finite element model using beam elements to estimate the strain concentration factor in concrete-coated pipelines under pure bending. The model includes the nonlinear material behavior and the slippage of the concrete coating. The bending moment and resulting strain from the beam model are compared with full-scale tests and solid element models. The comparison shows good agreement and confirms the model's accuracy. The results show that the beam model predicts strain distribution within the range of full-scale tests and solid models while reducing computational effort. The model can be applied to pipelines with different material properties, supporting design and optimization.

The fatigue performance of seamless carbon steel pipelines is essential for maintaining structural integrity under cyclic loading. This study examines the effect of external surface imperfections on fatigue behavior, focusing on their role in crack initiation and propagation. Six full-scale fatigue tests were performed on seamless pipe specimens (276.1 mm outer diameter x 14.27 mm wall thickness), made of grade 450 carbon steel, compliant with DNV-ST-F101. Three specimens developed through-wall fatigue cracks that originated at external surface imperfections and propagated inwards. All three samples exceeded their target fatigue life, indicating that the imperfections were within allowable limits defined by the fatigue design curve. Metallurgical analysis showed that larger imperfections would likely have caused earlier crack initiation due to increased local stress. All pipes passed both mill and third-party inspection before testing. The results indicate that current inspection and quality control methods may not identify small imperfections that influence fatigue performance. A review of industry standards identified differences in surface defect limits, inspection techniques, and repair procedures. Proposed improvements include standardizing grinding limits, adopting automated non-destructive testing methods, and applying risk-based acceptance criteria. These measures aim to improve fatigue resistance and support consistent pipeline integrity management.

Concrete coating is essential for enhancing the stability of subsea steel pipelines against hydrodynamic forces. However, stiffness mismatch at field joints leads to strain concentration, which may compromise the pipeline's structural integrity. Traditional methods for evaluating strain concentration, such as full-scale tests and finite element modelling using solid elements, produce acceptable results but are often costly, time-consuming, and impractical for routine application. This study presents a finite element model that employs beam elements to predict the strain concentration factor in concrete-coated pipelines subjected to pure bending moments. The model accounts for the nonlinear behavior of the concrete-coated pipeline material and the potential for concrete slippage. The relationship between the bending moment and the strain resulting from the beam element model is presented and compared with previous full-scale tests and finite element models using solid elements, demonstrating strong agreement and confirming the model's reliability and compliance with industry standards. The findings indicate that the beam model effectively predicts strain distributions while significantly reducing computational demands. Its adaptability to various material properties enhances its practicality in pipeline design and optimisation.

This paper studies the response of ELBOW31 and ELBOW31B element types under pure bending conditions, using shell and beam element models for benchmarking. Various model lengths are evaluated, showing that a model length of six pipe diameters exhibits a hardening effect when total strain exceeds 3.5%, though a strain up to 1% is deemed sufficient for pipeline design. The study examines the effects of ovality modes and boundary conditions such as NOWARP and NOOVAL on the bending response. ELBOW31 with one or two ovality modes yields accurate results, while additional ovality modes or zero ovality mode can lead to overprediction of the elastic bending moment capacity. The introduction of the NOWARP condition enhances the accuracy of the ELBOW31 model, while the NOOVAL condition alone produces unrealistic results. The simplified ELBOW31B model shows good agreement with the ELBOW31-NOWARP model but similarly overpredicts the bending moment when zero ovality mode is used. The study also finds that Poisson's ratio and model length have no significant impact on the bending response when no restrictions are applied. Additional analyses, as presented in Appendices A and B, highlight the importance of D/t ratios in pipeline performance. A D/t ratio of 20 offers a stiffer response with reduced ovalization, while a D/t ratio of 50 results in greater flexibility and increased ovalization. These findings provide valuable insights for the selection of element types, boundary conditions, and D/t ratios in robust pipeline design.

When modelling thermodynamic power cycles, it is typical to determine state properties through the use of an equation of state to evaluate parameters of interest. This results in a black-box-like model of the cycle with heavy reliance upon equations of state, leading to compromises in algorithm speed and stability. This paper presents a new approach for cycles within which expansion is contained within the two-phase region (which can include the trilateral flash cycle and partial evaporation organic Rankine cycle), based upon fundamental thermodynamic relations. Thermodynamic properties need only be determined for saturated and liquid states, which along with system constants and independent variables, allows for the rapid evaluation of important cycle parameters. In this paper, a definition is provided for a two-phase power cycle, governing equations are presented, and the thermodynamic derivation of the model is provided. The different types of working fluid are discussed with respect to the considerations which must be made for each. Lastly, a comparison between three simple algorithms (proposed model, hybrid model, and conventional model) is presented to demonstrate the validity of the proposed model and the improvements possible over the conventional method. Results show that the algorithm running the proposed model shows substantial improvements when compared to the conventional approach, demonstrating an improvement in runtime by a factor of 44.77, a reduction in cyclomatic complexity of 72.73%, and a reduction in reliance upon equations of state of 99.72%, with no compromises in accuracy.

The ever-growing concerns about global warming and the rapid depletion of fossil fuels have triggered a rising interest in the research for cleaner, more efficient, and cost-effective energy generation. Organic Rankine cycle systems have immense potential to become a strong alternative to conventional methods of energy generation. However, such systems’ efficiency is limited by the performance of the incorporated gas expanders or prime movers. Conventional gas expanders often utilize ports or cam-operated valves. Ported expanders offer limited efficiency and controllability and produce high emissions, causing a large amount of heated and compressed gas to be wasted. Cam-operated valves, in contrast, increase expansion performance compared to ported expanders; however, they have no variability and adaptability to changes in system parameters such as gas pressure, temperature, dryness fraction, and load variation, to name a few. On a positive note, this issue can be addressed by adopting a variable timing and fast-operating, control valve with an accurate and adaptive control mechanism at the expander inlet. A properly designed and controlled valve can greatly improve the system performance of gas expanders and pave the way for an efficient low-cost alternative energy generation. This manuscript provides a comparative review of recent progress on the design, modeling, optimization, and control aspects of valves for gas expanders. A clear pathway on the scope of further development is also drawn based on the present state of the art.

The leak of hydrocarbon-carrying pipelines represents a serious incident, and if it is in a gas line, the economic exposure would be significant due to the high cost of lost or deferred hydrocarbon production. In addition, the leakage of hydrocarbon could pose risks to human life, have an impact on the environment, and could cause an image loss for the operating company. Pipelines are designed to operate at full capacity under steady-state flow conditions. Normal operations may involve day-to-day transients such as the operations of pumps, valves, and changes in production/delivery rates. The basic leak detection problem is to distinguish between the normal operational transients and the occurrence of non-typical process conditions that would indicate a leak. To date, the industry has concentrated on a single-phase flow, primarily of oil, gas, and ethylene. The application of a leak-monitoring system to a particular pipeline system depends on environmental issues, regulatory imperatives, loss prevention of the operating company, and safety policy rather than pipe size and configuration. This paper provides a review of the recommended guidance for leak detection of subsea pipelines in the context of pipeline integrity management. The paper also presents a review of the capability and application of various leak detection techniques that can be used to offer a roadmap to potential users of the leak detection systems.

The ever-growing concerns about global warming and the rapid depletion of fossil fuels have triggered a rising interest in research for cleaner, more efficient and cost-effective energy generation. Organic Rankine cycle systems have immense potential to become a strong alternative to conventional methods of energy generation. However, such systems’ efficiency is limited by the performance of the incorporated gas expanders or prime movers. Conventional gas expanders often utilize ports or cam-operated valves. Ported expanders offer limited efficiency and controllability, and produce high emissions causing a large amount of heated and compressed gas to be wasted. Cam-operated valves, in contrast, increase expansion performance compared to ported expanders, however, they have no variability and adaptability to changes in system parameters such as gas pressure, temperature, dryness fraction, and load variation to name a few. On a positive note, this issue can be addressed by adopting a variable timing and fast-operating, control valve with an accurate and adaptive control mechanism at the expander inlet. A properly designed and controlled valve can greatly improve the system performance of gas expanders and pave the way for an efficient low-cost alternative energy generation. This manuscript provides a comparative review of recent progress on the design, modeling, optimization, and control aspects of valves for gas expanders. A clear pathway on the scope of further development is also drawn based on the present state of the art.

In this work, an artificial neural network (ANN)-based model is proposed to describe the input–output relationships in a Limaçon-To-Circular (L2C) gas expander with an inlet valve. The L2C gas expander is a type of energy converter that has great potential to be used in organic Rankine cycle (ORC)-based small-scale power plants. The proposed model predicts the different performance indices of a limaçon gas expander for different input pressures, rotor velocities, and valve cutoff angles. A network model is constructed and optimized for different model parameters to achieve the best prediction performance compared to the classic mathematical model of the system. An overall normalized mean square error of 0.0014, coefficient of determination (R2) of 0.98, and mean average error of 0.0114 are reported. This implies that the surrogate model can effectively mimic the actual model with high precision. The model performance is also compared to a linear interpolation (LI) method. It is found that the proposed ANN model predictions are about 96.53% accurate for a given error threshold, compared to about 91.46% accuracy of the LI method. Thus the proposed model can effectively predict different output parameters of a limaçon gas expander such as energy, filling factor, isentropic efficiency, and mass flow for different operating conditions. Of note, the model is only trained by a set of input and target values; thus, the performance of the model is not affected by the internal complex mathematical models of the overall valved-expander system. This neural network-based approach is highly suitable for optimization, as the alternative iterative analysis of the complex analytical model is time-consuming and requires higher computational resources. A similar modeling approach with some modifications could also be utilized to design controllers for these types of systems that are difficult to model mathematically.

This paper introduces a literature review of the accomplished research to calculate the strain concentration factor which shall be considered during the concrete coated subsea pipelines design. The strain concentration results from the discontinuity of the concrete coating which is applied to pipe joints to enhance the pipeline stability on the seabed. The paper introduces a definition of the strain concentration factor and a conclusive explanation of the work performed to calculate the strain concentration factor using the following three methods: full-scale tests, analytical models, and numerical models. The paper also introduces other works addressing the contribution of concrete coating to pipe stiffness. Literature indicates that whilst full-scale tests produce the most accurate values for the Strain Concentration Factor, due to cost implications, the method is limited to a small range of pipe sizes and coating properties. Although the analytical method produces acceptable results, prediction of strain concentration factor due to concrete coating sliding and beyond steel yield stress and concrete crushing limit is unpredictable. The numerical method using FE analysis indicates acceptable Strain Concentration factor values, however, careful consideration shall be taken due to possible modelling inaccuracies. The review shows that the strain concentration factor is mainly influenced by the thickness and strength of the concrete coating as well as the shear capacity of the external corrosion coating, whilst due to its low impact, the effect of the concrete coating reinforcement is not considered for most of the analysis due to low significance.

Renewable energy-based compact energy-generation systems based on the organic Rankine cycle (ORC) can be employed to meet the ever-growing thirst for affordable and clean energy. The overall performance and effectiveness of ORC systems are constrained by the low efficiency of the gas expander, specifically the positive displacement expander, which is responsible for energy conversion from the working fluid. This low-efficiency scenario can be significantly improved by employing a control valve to regulate and restrict the flow of the working fluid into the expander. A control valve can effectively curve the loss of costly compressed and energized working fluids by allowing them to expand in the expander chamber before discharging through the outlet port. They can thus be used to regulate the amount of energy yield and output power. In this work, two direct drive rotary valves (DDRVs) operated by a stepper motor (SM-DDRV) and rotary solenoid (RS-DDRV) are suggested, and the behavior of the valves is examined. The effect of friction and temperature on the valve response is also studied. Additionally, the effect of inlet control valves on the overall system performance of the limaçon expander is assessed. Thermodynamic properties such as the isentropic efficiency and filling factor are also computed. The effect of leakage due to valve response delay is analyzed at different inlet pressures. The performance indices are compared to the expander performance without any inlet valve. The SM-DDRV setup results in a 14.86% increase in isentropic efficiency and a 220% increase in the filling factor, whereas the RS-DDRV performs moderately with a 2.58% increase in isentropic efficiency and an 80% increase in the filling factor compared to a ported expander. The SM-DDRV provides better performance indices compared to the RS-DDRV and without valve setups. However, the performance of the limaçon expander with the SM-DDRV is sensitive to the inlet pressure and degrades at higher pressure. Overall, the valves proposed in this work present key insights into improving the performance characteristics of gas expanders of ORC systems.

Organic Rankine Cycle (ORC)–based small-scale power plants are becoming a promising instrument in the recent drive to utilize renewable sources and reduce carbon emissions. But the effectiveness of such systems is limited by the low efficiency of gas expanders, which are the main part of an ORC system. Limaçon-based expansion machines with a fast inlet control valve have great prospects as they could potentially offer efficiencies over 50%. However, the lack of a highly reliable and significantly fast control valve is hindering its possible application. In this paper, a push–pull solenoid valve is optimized using a stochastic optimization technique to provide a fast response. The optimization yields about 56–58% improvement in overall valve response. A performance comparison of the initial and optimized valves applied to a limaçon expander thermodynamic model is also presented. Additionally, the sensitivity of the valve towards a changing inlet pressure and expander rotor velocity is analyzed to better understand the effectiveness of the valve and provide clues to overall performance improvement.

Limaçon rotary machines are the heart of power generation systems, especially small- and micro-scale ones. These machines are the prime movers that play the main role in converting the potential energy to other useful forms of work, such as mechanical and/or electrical; the generated energy can also be stored in batteries or in the form of hydrogen. The focus of this paper is on the working of this limaçon technology, and the embodiments and mechanical drives to produce the unique motion of these machines. This paper will also discuss the related power-generating cycles and control schemes.

Improving the ways in which power is generated and devising new systems with higher efficiencies and lower environmental footprints are important endeavours. Towards this end, the partial evaporation organic Rankine cycle (PE-ORC) presents itself as a viable candidate with the development and refinement of prime movers capable of handling two-phase flow. Additionally, the development of micro-CHP systems using such a cycle represents an untapped potential towards these goals. Through the design and simulation of a PE-ORC based micro-CHP system and the optimisation of it using the multi-objective grey wolf optimiser (MOGWO), the potential of the PE-ORC is investigated and a subsequent experimental design becomes a more tangible possibility. Performance metrics considered are the thermal and exergetic efficiencies and the net work output, while consideration is also given to mass flow rates and the Mach number. Findings suggest that the PE-ORC is capable of achieving high exergetic efficiencies while producing desirable power output levels, however, consideration must be given to the mass flow rates and Mach number during optimisation as these values can be excessively or unfeasibly large in a number of cases.

This paper outlines the necessity and suitability of in-line inspection (ILI) using intelligent pigging for Corrosion Resistant Alloy (CRA) subsea clad pipelines through an incident that occurred during a baseline survey performed on a 20-inch y CRA clad pipeline of 2.7 km long. In this incident, an ultrasonic (UT) intelligent pigging tool was impacted and resulted in damage to the pipeline's clad layer. This damage was due to the collosion of the sealing pigs with the rear of the UT intelligent pigging tool, resulting in the UT intelligent pigging tool to get stuck and stop at the end of the pipeline. Pressure surges were used to dislodge the UT intelligent pigging tool, but caused the UT pig to be crashed into the pig receiver, resulting in severe damage to the UT pigging tool. The analysis of the metal swarf recovered from the pig receiver revealed that the damage was limited to the pipeline's clad layer. It was also revealed that a bypass has occurred to the sealing pigs causing damage to the sensor carriers of the intelligent pigging tool.

Positive displacement compressors are essential in many engineering systems, from domestic to industrial applications. Many studies have been devoted to providing more insights into the workings and proposing solutions for performance improvements of these machines. This study aims to present a systematic review of published research on positive displacement compressors of various geometrical structures. This paper discusses the literature on compressor topics, including leakage, heat transfer, friction and lubrication, valve dynamics, port characteristics, and capacity control strategies. Moreover, the current status of the application of machine learning methods in positive displacement compressors is also discussed. The challenges and opportunities for future work are presented at the end of the paper.

The operating lifespan of pipelines is limited, defined by their specific design codes and specifications, with the economic justification for this being determined primarily by the pipeline owner. During its operational lifespan, a pipeline’s integrity is affected mainly by the quality of the hydrocarbons being transported. The integrity of a pipeline can be maintained with regular inspections and maintenance/cleaning programmes followed from installation to commissioning. As production matures and declines, operators face several decisions concerning the pipeline’s future. There are several potential scenarios, and each should be assessed on a case-by-case basis for any specific pipeline in question. The industry best practices outline the minimum requirements for the safe decommissioning of pipelines. However, there currently need to be international specifications to be followed for the decommissioning of disused offshore pipelines. This paper aims to provide insight into the decommissioning and abandonment of offshore pipelines. Also, this article provides case studies for the decommissioning of subsea pipelines.

The need for the utilisation of marine risers in deep seas has increased in recent years and this is due to increased drilling explorations with the shift in trend from shallower to deep and deeper waters. Also, there have been increased applications in sea-crossing infrastructure resulting in the need for longer risers, leading to a significant weight increase of marine risers used. Composite materials can thus be utilised in marine riser engineering to provide lightweight, fatigue-resistant, corrosion-resistant, low-bending stiffness and high-strength characteristics. In this paper, the history and potential of composite marine risers, including the first successful deployment of a composite riser joint offshore on the Heidrun Platform in 1995, are reviewed. The paper also discusses the advances achieved on composite marine risers for deep waters and presents some recommendations on their use, in light of their current significance and growth.

Organic Rankine Cycle (ORC) based small-scale energy generation systems can be utilized to address the rapidly increasing demand for low-cost power. But the overall efficiency of these systems is limited by the efficiency of the gas expander which extracts work from the working fluid. This efficiency can be greatly improved by regulating the flow of working fluid into the expander chamber using a control valve. In this manuscript, a rotary valve driven by a direct drive stepper motor (DDRV) is proposed and the dynamics of the valve is studied. The overall performance of the limaçon expander equipped with this valve on the inlet port is also analyzed. The thermodynamic performance of the system such as isentropic efficiency and filling factor are calculated. An increase in isentropic efficiency of 14.86% with a decrease in filling factor of 16.88% is achieved compared to the ported, without an inlet valve, expander.