Offshore Pipelines Research Articles

Reliability assessment for pipelines corroded by longitudinally aligned defects

Internal corrosion poses a significant threat to offshore pipeline services. Toward offshore pipeline integrity management, this paper aims to use Finite Element Method (FEM) to assess the reliability of corroded pipelines. The FEM analysis was conducted using ABAQUS software, facilitated through Python scripts, to optimize the modeling process on a large scale. Additionally, the input database was generated through a random sampling method using the Latin Hypercube Sampling (LHS) method. The reliability of 32” oil and gas offshore internally corroded pipelines has been evaluated by fragility curve assessment along with Incremental Pressure Analysis (IPA) which is a new method inspired by Incremental Dynamic Analysis (IDA). Multiple corrosion defects pose a higher risk to offshore pipelines during service, with potentially more severe consequences than a single defect alone. Therefore, the interaction of corrosion defects has been considered in this study. Following the reliability assessment the most appropriate Probability Density Function (PDF) for the Maximum Von Mises Stress (MVMS) and failure probability at various Internal Pressure (IP) and longitudinal spacing (Sl) levels has been evaluated.

Characteristics and migration of subaqueous sand dunes influenced by internal solitary waves in the Dongsha Region, Northern South China Sea

Seabed data acquired from the Dongsha Region in the northern South China Sea (SCS) revealed the detailed morphology of sand dune fields on the upper continental slope, at depths between 230 and 1240 m. High-resolution multibeam echosounder bathymetry and multichannel seismic reflection data were used to describe and interpret the distribution, characteristics, and migration of these sand dunes. The sand dunes were distributed as patches on a generally gentle continental slope (gradients≤0.58°), on a seafloor mainly covered by silty and coarse sand. The dunes exhibited distinctly different distribution patterns, geometries, and migration behavior. The trough-to-trough wavelength ranged from 47 to 555 m, the height was 0.1 to 19.8 m, the crest length was 100 m to 10s of km, and the dominant orientation was NE-SW. Based on their distribution and characteristics, the sand dunes were further categorized into (i) sinuous, (ii) barchan, (iii) reticular, (iv) restricted, and (v) superimposed types. Most sand dunes migrated to both NW and SE directions. We infer that, in the Dongsha Region, northern SCS, sand dunes formed and migrated due the world's largest observed internal solitary waves (ISWs). Wave-wave and wave-topography interactions occur as ISWs propagate and undergo polarity conversion during shoaling process, reflection, refraction, diffraction at the Dongsha Atoll. These processes bring about variable and complex local hydrodynamic conditions in the Dongsha Region, dissipate vast amounts of energy, erode the seafloor, and supply the sediment and energy required to sustain the formation and migration of very large sand dunes. Our findings not only enhance our understanding of the intricate relationships between topographic and geomorphologic evolution, sedimentary dynamics and mesoscale motions, but also hold significant importance for various hydrographic applications, such as navigation and submarine pipeline installation.

Analysis of the Drag-Reduction Ability of the Layout and Cross-Sectional Shapes of Subsea Structures in the Critical Flow Mode

Introduction. Slender structures of subsea energy production systems are under constant influence of currents and waves. Hydrodynamic loads result from the interaction of subsea pipelines, umbilicals, equipment supports with fluid flows, and lead to the vortex formation in the area behind the structures. Vortex-induced forces are the sources of the cyclic loading. They accelerate gradually the fatigue damage, which may result in a failure. One of the ways to reduce the loads on subsea structures is to alter the shape of a cross-section, taking into account the flow regime. Dependence of the resulting hydrodynamic loads on the cross-sectional shape and relative position of structures has not been studied in details for the uniform flow in the critical mode. The current work is aimed at filling this gap. The research objective is to consider the impact of the distance between the structures, and also, the presence of a D-shaped structure, placed upstream relative to the group of three cylinders of different cross-sectional shapes.Materials and Methods. The computational fluid dynamics approach was used in this work for numerical simulations of vortex-induced forces in the ANSYS Fluent software for cylinder with D = 0.3 m. Modelling was conducted with the Detached Eddy Simulation (DES) method, which combined advantages of the Reynolds-averaged Navier-Stokes equation (RANS) method and the Large Eddy Simulation (LES) method. The object of the research was the system of four structures in the 2D computational domain, which included the upstream D-shaped cylinder and the main group of three cylinders with the circular, squared and diamond shapes of the cross-section. The transient process was considered, where structures were under the influence of the uniform flow in the critical regime at Re = 2.5×10⁵.Results. Five sets of data were obtained in simulations for the time-dependent coefficients of the lift and drag forces: for the main system — of the D-shaped, circular, square and diamond structures, and also for the four systems — of only D-shaped, only circular, only square and only diamond shaped structures. Additional analysis was conducted for the effect of the distance between the structures on the amplitude of fluctuating hydrodynamic force coefficients. The obtained results are presented as time histories of coefficients of the lift and drag forces, frequency analysis and contours of velocity, pressure and vorticity fields. The results indicate a positive effect of the upstream D-shaped structure on reducing the drag force, acting on the central structure in the group of three cylinders located downstream.Discussion and Conclusion. The results of the performed studies facilitate the informed decisions regarding the arrangement of subsea structures in a group of four objects, depending on the cross-sectional shape and the distance between the structures. The upstream D-shaped structure provides reducing the hydrodynamic drag force acting on the central structure in the downstream group of three structures, thereby slowing the fatigue accumulation and increasing the time of safe operation.

Nomograph derivation for underwater sour gas releases in shallow waters based on computational fluid dynamics simulations

Ruptured underwater pipelines releasing sour gas (i.e., natural gas with high concentrations of H2S) pose significant threats to environmental safety due to their toxic and contaminative properties. This study suggests a transient Eulerian-Eulerian multiphase computational fluid dynamics (CFD) model for assessing the environmental impact of sour gas releases in shallow, ecologically sensitive waters. Employing the Realizable k-ε turbulence model and additional bubble plume mechanisms, the model was rigorously validated against well-documented experimental data, showing high levels of agreement across multiple metrics. Key environmental safety parameters—such as rise time and H2S surface gas concentration, indicative of toxic exposure risk to aquatic life and human health—were extracted for multiple release scenarios. To present generalized and easily accessible data, these parameters were nondimensionalized and incorporated into a nomograph, enabling environmental risk assessments to be conducted four orders of magnitude faster than with high-fidelity simulations. The study emphasizes the nomograph's utility in rapid, environmentally relevant risk assessment and emergency planning for mitigating the impact of sour gas spills. An error and sensitivity analysis revealed uncertainties of ±7 % for rise time and ±58 % for surface gas concentration, pinpointing avenues for future research.

Analysis of the Effect of Using Concrete Mattresses on Subsea Pipelines

Analysis of the Effect of Using Concrete Mattresses on Subsea Pipelines

Corrosion behavior of X60 pipeline steel in the presence of Sulfate Reducing Bacteria cultured in seawater and mud from the East China Sea

Sulfate-reducing Bacteria (SRB) corrosion is a serious threat to the safety of marine pipelines.To reveal the influence of the corrosion behavior of X60 pipeline steel in the presence of SRB cultured in seawater and mud from the East China Sea The corrosion behavior of X60 pipeline steel was studied with weight loss measurements, microstructure and membrane composition analysis, electrochemical measurements The corrosion rate in sterile seawater is 0.11 mm/y, whereas, in SRB-infested seawater, it increases by 245 % to 0.38 mm/y. In sterile sea mud, the corrosion rate is 0.15 mm/y, but in SRB-infested sea mud, it increases by 87 % to 0.28 mm/y. In the corrosive environment of seawater and mud in the East China Sea, SRB significantly accelerates the microbial corrosion of X60 pipeline steel. These findings provide theoretical guidance for further research on SRB corrosion mechanisms and corrosion control of marine pipelines.

A Low-Frequency Vibration Sensor Based on Ball Triboelectric Nanogenerator for Marine Pipeline Condition Monitoring.

Marine pipeline vibration condition monitoring is a critical and challenging issue, on account of the complex marine environment, while powering the required monitoring sensors remains problematic. This study introduces a vibration sensor based on a ball triboelectric nanogenerator (B-TENG) for marine pipelines condition monitoring. The B-TENG consists of an acrylic cube, polyester rope, aluminum electrodes, and PTFE ball, which converts vibration signals into electrical signals without the need for an external energy supply. The experimental results show that B-TENG can accurately monitor the frequency, amplitude, and direction of vibration in the range of 1-5 Hz with a small error of 0.67%, 4.4%, and 5%, and an accuracy of 0.1 Hz, 0.97 V/mm, and 1.5°, respectively. The hermetically sealed B-TENG can monitor vibration in underwater environments. Therefore, the B-TENG can be used as a cost-effective, self-powered, highly accurate vibration sensor for marine pipeline monitoring.

Application of a Statistical Regression Technique for Dynamic Analysis of Submarine Pipelines

Application of a Statistical Regression Technique for Dynamic Analysis of Submarine Pipelines

Взрывная дегазация Земли на полуострове Ямал и прилегающей акватории Карского моря

Remote sensing data from space and using UAVs make it possible to solve a wide range of tasks related to the study of Earth degassing processes in the Arctic. For the first time, via comprehensive aerospace research on the Yamal Peninsula, we have discovered 4992 zones of gas blowouts (explosions) in the form of craters (pockmarks) at the bottom of 3551 thermokarst lakes and 16 rivers. In addition, we have identified another 669 zones of explosive degassing in the coastal zones of the Kara Sea, mainly in gulfs, estuaries and bays. Taking into account the Yugorsky Peninsula and Bely Island, we have detected 6022 explosive degassing zones in the studying region, including 905 ones offshore. We have proved previously made conclusions that the Neytinsko-Seyakhinsky and Sabetta districts are the most gas-explosive. It is substantiated that possible intense natural degassing of the Earth, especially occurring in the process of degradation of subaquatic permafrost and dissociation of gas hydrates, can radically change the elastic-strength properties of bottom soil, while its saturation with gas can disrupt conditions for the construction of various objects, including underwater gas pipelines. Widespread gas blowouts in the north of Western Siberia with the formation of craters on land and offshore can lead to emergencies and even disasters at oil and gas industrial facilities and to fires in the tundra.

Modeling the Thermal-Induced Buckling of Offshore Pipelines in Clay Using the Effective Stress RITSS Method in Three Dimensions

Modeling the Thermal-Induced Buckling of Offshore Pipelines in Clay Using the Effective Stress RITSS Method in Three Dimensions

Unleashing the Potential of a Hybrid 3D Hydrodynamic Monte Carlo Risk Model for Maritime Structures’ Design in the Imminent Climate Change Era

Submarine pipelines have become integral for transporting resources and drinking water across large bodies. Therefore, ensuring the stability and reliability of these submarine pipelines is crucial. Incorporating climate change impacts into the design of marine structures is paramount to assure their lifetime safety and serviceability. Deterministic design methods may not fully consider the uncertainties and risks related to climate change compared to risk-based design models. The latter approach considers the future risks and uncertainties linked to climate and environmental changes, thus ensuring infrastructure sustainability. This study pioneers a Hybrid 3D Hydrodynamic Monte Carlo Simulation (HMCS) Model to improve the reliability-based design of submarine pipelines, incorporating the effects of climate change. Current design approaches may follow deterministic methods, which may not systematically account for climate change’s comprehensive uncertainties and risks. Similarly, traditional design codes often follow a deterministic approach, lacking in the comprehensive integration of dynamic environmental factors such as wind, waves, currents, and geotechnical conditions, and may not adequately handle the uncertainties, including the long-term effects of climate change. Nowadays, most countries are developing new design codes to modify the risk levels for climate change’s effects, such as sea-level rises, changes in precipitation, or changes in the frequency/intensity of winds/storms/waves in coastal and marine designs. Our model may help these efforts by integrating a comprehensive risk-based approach, utilizing a 3D hydrodynamic model to correlate diverse environmental factors through Monte Carlo Simulations (MCS). The hybrid model can promise the sustainability of marine infrastructure by adapting to future environmental changes and uncertainties. Including such advanced methodologies in the design, codes are encouraged to reinforce the resilience of maritime structures in the climate change era. The present design codes should inevitably be reviewed according to climate change effects, and the hybrid risk-based design model proposed in this research should be included in codes to ensure the reliability of maritime structures. The HMCS model represents a significant advancement over existing risk models by incorporating comprehensive environmental factors, utilizing advanced simulation techniques, and explicitly addressing the impacts of climate change. This innovative approach ensures the development of more resilient and sustainable maritime infrastructure capable of withstanding future environmental uncertainties.

Assessment of a Full-Electric Floating Liquefied Natural Gas Concept for Harsh Sea State Conditions at Remote Ultra-Deepwater Locations

_ This work describes an offshore gas monetization solution for harsh environmental conditions at ultra-deepwater and remote locations, as an alternative to conventional onshore plants associated with long subsea pipelines for Greenfield projects. Although gas-to-liquids and marine compressed natural gas are initially evaluated, associated gas is supposed to be exported from deepwater floating production storage and offloading units to a central floating liquefied natural gas (FLNG) facility for additional treatment, fractionation, and liquefaction, producing liquefied natural gas (LNG) and liquefied petroleum gas (LPG) for further tandem offloading. To demonstrate the technical feasibility of the proposed FLNG, its key technologies are reviewed, including liquefaction process selection, cargo containment system, station-keeping, offloading, and power generation. A full-electric FLNG is proposed, replacing conventional feed gas power generation systems with inner hull nuclear power modules, envisaging neutral CO2 emissions and earlier first LNG drop milestone achievement. The FLNG general arrangement is developed, along with its internal cargo tanks layout, for preliminary LNG and LPG production rundown and feed gas throughput. Numerical analyses are carried out to show that static and dynamic tilt criteria can be met, even for harsh sea states. Gas import riser configurations for the challenging ultra-deepwater location are outlined, after appropriate FLNG station-keeping analyses, in addition to a feasibility assessment of seawater intake risers, aiming for an overall gas plant efficiency increase. Keywords FLNG; FPSO; LNG/LPG; associated gas; design (general)

Assessment of transboundary environmental damage to the Baltic sea basin during construction and operation of the offshore pipeline system

Assessment of transboundary environmental damage to the Baltic sea basin during construction and operation of the offshore pipeline system

Incompressible Smoothed Particle Hydrodynamics Simulation of Sediment Erosion around Submarine Pipelines

Sediment erosion around submarine pipelines is a popular topic, widely investigated in both ocean and submarine-pipeline engineering. In this paper, the incompressible smoothed-particle hydrodynamics (ISPH) method is modified for simulation of local scouring process around the submarine pipeline under the action of unidirectional flow. The erosion model is based on the Clear Water Particle–Turbid Water Particle–Critical Shear Stress (CWP-TWP-CSS) concept, and a sand–water two-phase model is proposed to deal with the sediment-entrained flow. The results of the numerical simulation are compared with the experimental data to verify the accuracy and applicability of the numerical model. The scouring process around the pipeline is investigated under different conditions, i.e., pipeline diameters, gap ratios, and flow velocities. The ISPH model is further used to study the flow characteristics of the scour pits around the submarine pipeline and the influence of the vortices on the maximum scour depth, to provide a theoretical basis for the stability design of submarine pipelines.

A path to make well-informed decisions when considering the decommissioning of subsea pipelines

Australia’s law mandates the removal of infrastructure once not in use unless the Titleholder can demonstrate an equal or superior safety and environmental outcome. Around 100 infield and export pipelines in Australian waters, with an approximate total length of 5000 km, are nearing their end-of-life period. Three common decommissioning options are considered for subsea pipelines: complete removal, partial removal, or in-situ abandonment. Decommissioning these pipelines will cost an estimated US$13 billion, ~33% of the cumulative Australian offshore decommissioning liability, should the full removal option be selected. When decommissioning subsea pipelines, it is essential to consider that they have been exposed to hazardous fluids and aggressive environments. Careful assessments should determine the recyclability of recovered materials, decontamination, and the environmental risks associated with each decommissioning option. A holistic approach is needed to identify and quantify contaminants in subsea pipelines. In the early stages of decommissioning, planning, sampling, and laboratory testing are necessary to identify plastic coating types, degradation mechanisms, constituents released to the environment, types and mechanisms related to mercury/naturally occurring radioactive materials, and chemical stability. This paper aims to identify and present effective methods for addressing the impact of pipeline constituents on the Marine Environment Assessment while assessing potential decommissioning options and explains how tools can support decision-making. In summary, decommissioning subsea pipelines requires careful assessment and planning to ensure environmental and safety compliance. The paper provides a guide to understanding the process, highlighting the importance of quality assurance, risk assessment, and the selection of appropriate decommissioning options.

Analysis of an existing hydrocarbon gas pipeline for conversion to dense phase CO2 service

Esso Australia is investigating the feasibility of a carbon capture and storage (CCS) project in East Gippsland, Victoria. Known as the South-East Australia Carbon Capture and Storage (SEA CCS) Hub, the project aims to re-purpose existing infrastructure and offshore depleted hydrocarbon reservoirs to store carbon dioxide (CO2). The project aims to reduce greenhouse gas emissions from Esso’s Longford Gas Conditioning Plant, and to unlock future CCS opportunities for Australia. One option identified as part of the SEA CCS feasibility was to convert part of the existing onshore section of the Barracouta 450 mm gas pipeline to Longford Gas Plant (BTA450-LFD), Licence PL/1 under the Victorian Pipeline Act, to dense phase CO2 service. This paper documents the initial findings of the potential for the onshore section of the BTA450 for conversion, with particular emphasis on brittle and ductile fracture control considerations. In summary, when attempting to convert existing hydrocarbon gas pipelines for CO2 service, operators need to undertake an appropriate assessment of fracture control considerations. The insights of this paper may serve as a useful guide document for assessing other existing onshore pipelines for CO2 service conversion. Due to the thermal modulation effect of the surrounding water for subsea pipelines, this guidance does not apply to subsea pipeline sections.

Requalification of pipelines for CO2 transport – giving new life to the Bayu-Undan and Reindeer pipelines

Australia has in the order of 3500 km of offshore pipelines currently operating in Commonwealth waters which will require either re-use or decommissioning at the end of hydrocarbon service. Santos are currently developing the Bayu-Undan and Reindeer CCS (carbon, capture and storage) Projects, to make use of the depleted hydrocarbon reservoirs to store carbon dioxide (CO2) via existing offshore infrastructure. A key aspect of these projects is the requalification of existing offshore hydrocarbon pipelines to transport CO2, both of which have been in operation for 10–20 years. The Bayu-Undan and Reindeer pipelines were designed and operated for (a) distinctly different hydrocarbon services and (b) with no initial consideration for future CO2 service. This presents two unique technical starting points in the delivery of safe and robust conversion to CO2 service. Using knowledge gained from this, the paper provides an outline of the key technical considerations to requalification of pipelines unique to the combination of life extension and CO2 service. These are framed in the context of existing industry codes and technical challenges with CO2 pipelines. The outcomes are structured against typical phases in the project lifecycle and opportunities for optimisation of future CO2 re-purposing projects are proposed.

Sterically Hindered Oleogel-Based Underwater Adhesive Enabled by Mesh-Tailoring Strategy.

Underwater adhesives hold significant relevance in daily life and numerous industrial applications. Despite considerable efforts, developing scalable, high-performance underwater adhesives through a simple and effective method remains a formidable challenge. This study presents a novel mesh-tailoring strategy for in situ, rapid, and ultrastrong oleogel-based underwater adhesives (OUA), which comprises a highly crosslinked polyurethane network with a matching mesh size (≈2.22nm) that precisely entraps bio-based epoxidized soybean oil (ESO) molecules (≈2.31nm) by steric hindrance effect. This oleogel exhibits unprecedented robust mechanical properties (≈35MPa) and maintains stability under extreme conditions, including high temperatures (100°C), high pressures (30MPa), and immersion in various solvents (water, ethanol, or ESO). In particular, this oleogel displays high hydrophobicity, rapid curing, and strong interface affinity, resulting in ultrahigh underwater adhesion strength (up to 2.13MPa) and exceptional substrate universality. Moreover, the remarkable environmental adaptability and stability of OUA enable its use in harsh aqueous environments, including acidic/alkaline, saline, and extreme temperature solutions. The comprehensive capabilities of the OUA underscore its potential for building underwater structures, repairing leaky containers, and sealing broken submarine pipelines. This research establishes the foundation for the designing of next-generation underwater adhesives and offers fresh perspectives for exploring oleogel-based materials.

Failure assessment of corroded offshore pipelines using code-based approaches and a combination of numerical analysis and artificial neural network

The main purpose of the present paper is to investigate the failure pressure and the remaining life of the corroded offshore pipelines utilizing code-based methods such as ASME B31G, modified ASME B31G, DNV RP-F101 and FFS Level-1. Besides, the results of these approaches are compared with the responses of Finite Element Method (FEM) using Artificial Neural Network (ANN) model. To this purpose, the probability distribution of the corrosion defect length and depth as well as the corrosion rate values are obtained from an In-Line Inspection (ILI) survey of an offshore pipeline project in the Persian Gulf. In addition, a 3D verified numerical model of a corroded pipeline is constructed to conduct the numerical analyses. Using the numerical analysis data, a Multi-Layer Perceptron (MLP) model is created to estimate the failure pressure of the pipeline with arbitrary defect dimensions. Moreover, the remaining life of the corroded pipeline is quantified in order to prevent the catastrophic consequences of the pipeline failure. The results show that the MLP model is capable of estimating the failure pressure of the corroded offshore pipeline with quite acceptable accuracy compared with the mentioned code-based methods. Furthermore, the calculated failure pressure of the corroded pipeline can be sorted in ascending order as: (1) FFS-Level 1 (2) ASME modified B31G (3 & 4) ASME B31G & DNV RP-F101 (5) FEM + MLP. In fact, the failure pressure and the remaining life calculated by DNV RP-F101 are closer to the FEM + MLP results for the defects with small and medium dimensions. Diversely, the DNV RP-F101 method underestimates the failure pressure of the corroded pipeline when the defect dimensions become larger.

Offshore oil and gas infrastructure plays a minor role in marine metapopulation dynamics

Decommissioning consequences of offshore oil and gas infrastructure removal on marine population dynamics, including connectivity, are not well understood. We modelled the connectivity and metapopulation dynamics of three fish and two benthic invertebrate species inhabiting the natural rocky reefs and offshore oil and gas infrastructure located in the Bass Strait, south-east Australia. Using a network approach, we found that platforms are not major sources, destinations, or stepping-stones for most species, yet act as modest sources for connectivity of Corynactis australis (jewel anemone). In contrast, sections of subsea pipelines appear to act as stepping-stones, source and destination habitats of varying strengths for all study species, except for Centrostephanus rodgersii (long-spined sea urchin). Natural reefs were the main stepping-stones, local source, and destination habitats for all study species. These reefs were largely responsible for the overall metapopulation growth of all study species (average of 96 % contribution across all species), with infrastructure acting as a minor contributor (<2 % average contribution). Full or partial decommissioning of platforms should have a very low or negligible impact on the overall metapopulation dynamics of the species explored, except C. australis, while full removal of pipelines could have a low impact on the metapopulation dynamics of benthic invertebrate species and a moderate impact on fish species (up to 34.1 % reduction in the metapopulation growth). We recommend that the decision to remove offshore infrastructure, either in full or in-part, be made on a platform-by-platform basis and consider contributions of pipelines to connectivity and metapopulation dynamics.