Polyester Mooring Lines Research Articles

Biocatalytic depolymerization of waste polyester mooring lines from oil and gas offshore platforms made of poly(ethylene terephthalate) (PET)

AbstractBACKGROUNDThe global concern of plastic pollution in the environment has consistently been emerging in the past years. As one of the main polymers constituting single‐use products, poly(ethylene terephthalate) (PET) is found in a plethora of packages for diverse sectors, and its recycling has been broadly addressed. However, other relevant industrial PET wastes have not been under investigation for recycling purposes, such as the polyester mooring lines (PMLs) used to anchor offshore oil and gas floating platforms. In this study, the fibers from either new or used PMLs were characterized according to different techniques (differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, nuclear magnetic resonance and scanning electron microscopy–energy‐dispersive X‐ray spectroscopy), which allowed the interpretation of their chemical and thermal properties. The fibers were then used in depolymerization reactions under the catalysis of the cutinase enzyme from Humicola insolens and under different process conditions (fiber length, buffer composition, enzyme dosage, temperature, pH).RESULTSCharacterization of PMLs revealed inorganic incrustation in the external fibers, and very similar crystallinity degrees. The molecular weight, on the other hand, was found to be lower in new mooring lines (27 489 g mol−1) as compared to used mooring lines (35 813–36 785 g mol−1). Throughout depolymerization reactions, a total concentration increase of terephthalic acid of up to 7.4 times (2593 μmol L–1) was achieved.CONCLUSIONThe results proved the concept that the studied cutinase can act on PET chains. To the best of our knowledge, this is the first report to describe an enzyme‐catalyzed depolymerization of PET from mooring lines, and the results add relevant knowledge for a circular economy of plastic products.

A Look at the Aasta Hansteen Norwegian Deepwater Spar FPSO

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper OTC 29222, “Aasta Hansteen Spar FPSO—A Pioneer in Norwegian Deepwater,” by Torolf Christensen, Stig Arne Witsøe, and Helge Hagen, Equinor, et al., prepared for the 2019 Offshore Technology Conference, Houston, 6–9 May. The paper has not been peer reviewed. Copyright 2019 Offshore Technology Conference. Reproduced by permission. The complete paper describes the overall project execution of the Aasta Hansteen field development on the Norwegian Continental Shelf (NCS) north of the Arctic Circle. It is the deepest field yet developed on the NCS in 1300 m of water. In a harsh environment, with no other offshore installations in the area, the field is being developed with a spar floating, production, storage, and offloading (FPSO) structure using steel catenary risers and polyester mooring lines. Business Case The field is 300 km off the coast of northern Norway and 140 km from the nearest offshore installation. The field was discovered in 1997, with investment decision taken in December 2012 and production begun in December 2018. Total investment in facilities and infrastructure (including pipeline and modifications at Nyhamna) is approximately $7 billion. Equinor operates the field on behalf of its partners, Wintershall (24%), OMV (15%), and ConocoPhillips (10%). The field’s rich gas is exported through a 482-km-long, 36-in. pipeline to an on-shore processing plant at Nyhamna for further processing to sales gas. From there, the gas is exported to the European market. Stabilized condensate is stored in the spar FPSO and offloaded to shuttle tankers. The development of the field with the platform facilities and the Polarled pipeline was a strategic decision to open a new gas region in the Norwegian Sea and connect it to Europe by the NCS gas infrastructure. The development solution will serve as a gas hub enabling tie-in of future production from discoveries and prospects in the area. The objective of the Aasta Hansteen development is to maximize the recovery of the Aasta Hansteen reserves and to achieve maximum value creation in the value chain. Estimated recoverable reserves are 51 billion scm rich gas and 0.6 million scm condensate. The reserves consist of three separate discoveries—Luva, Haklang, and Snefrid Sør—all in the Nise formation and within the same production license. The development of Aasta Hansteen has been executed as a parallel development of the Polarled pipeline project to establish a new gas transport pipeline from Aasta Hansteen to Nyhamna. The pipeline has several tie-in points from Aasta Hansteen to the Nyhamna gas-processing plant. Snefrid Nord, the first subsea tieback development, is already being developed. The complete paper provides a brief description of the Polarled project.

Design of Mooring Solutions and Array Systems for Point Absorbing Wave Energy Devices—Methodology and Application

Abstract Most of the ocean energy technologies are considered to be in a pre-commercial phase and need technical development. This study focuses on the design of mooring solutions and compares array systems of a specific floating point-absorbing wave energy converter (WEC) developed by the company Waves4Power. A full-scale prototype of the WEC is installed in Runde (Norway) where it is moored with three polyester mooring lines, each having one floater and one gravity anchor. Based on this reference installation, the method of systems engineering was used to propose 22 conceptual mooring solutions for different array systems. They were compared and reduced to four top concepts in a systematic elimination procedure using Pugh and Kesselring matrices. The top concepts were assessed in detail by means of levelized cost of energy (LCOE), life cycle analysis (LCA), and risk analyses. The fatigue life of the mooring lines and the energy capture were calculated using results obtained from coupled hydrodynamic and structure response analyses in the dnv-gl deepc software. Two final concepts were proposed for the water depths 75 and 200 m.

Active truncation of slender marine structures: Influence of the control system on fidelity

Performing hydrodynamic model testing of ultra-deep water floating systems at a reasonable scale is challenging, due to the limited space available in existing laboratories and to the large spatial extent of the slender marine structures that connect the floater to the seabed. In this paper, we consider a method based on real-time hybrid model testing, namely the active truncation of the slender marine structures: while their upper part is modelled physically in an ocean basin, their lower part is simulated by an adequate numerical model. The control system connecting the two substructures inevitably introduces artefacts, such as noise, biases and time delays, whose probabilistic description is assumed to be known. We investigate specifically how these artefacts influence the fidelity of the active truncation setup, that is its capability to reproduce correctly the dynamic behaviour of the system under study. We propose a systematic numerical method to rank the artefacts according to their influence on the fidelity of the test. The method is demonstrated on the active truncation of a taut polyester mooring line.

An enhanced stiffness model for elastic lines and its application to the analysis of a moored floating offshore wind turbine

The performance of a polyester mooring line is non-linear and its elongation plays a significant role in the dynamic response of an offshore moored structure. However, unlike chain, the tension–elongation relationship and the overall behavior of elastic polyester ropes are complex. In this paper, by applying an enhanced stiffness model of the mooring line, the traditional elastic rod theory has been extended to allow for large elongations. One beneficial feature of the present method is that the tangent stiffness matrix is symmetric; in non-linear formulations the tangent stiffness matrix is often non-symmetric. The static problem was solved by Newton–Raphson iteration, whereas a direct integration method was used for the dynamic problem. The computed mooring line tension was validated against the proprietary OrcaFlex software. Results of mooring line top tension predicated by different elongations are compared and discussed. The present method was then used for a simulation of an offshore floating wind turbine moored with taut lines. From a comparison between linear and non-linear formulations, it is seen that a linear spring model under-estimates the mean position when the turbine is operating, but over-estimates the amplitude of the platform response at low frequencies when the turbine has shut down.

Effect of Mooring Line Properties and Fairlead Slopes on the Restoring Behavior of Offshore Mooring System

Mooring lines are used as station keeping systems for the deep-water floating offshore platforms. Mooring lines have considerable effect on the project overall cost. Therefore, it is necessary to economize their cost by choosing appropriate material and configuration which, in turn give the required responses for the platform by possessing good restoring capability. Hence, a numerical study has been conducted on the restoring behavior of the mooring system for different mooring line materials, line diameters and fairlead slopes. Two mooring systems consisting of mooring lines arranged unsymmetrical were considered. Assuming the drag forces on the mooring lines to be negligible and the change in the line geometry as insignificant, the mooring system has been analyzed using the quasi-static analysis. The numerical model thus developed has been validated using experimental model test data and a parametric study was conducted using the parameters mentioned. It can be concluded that the polyester mooring lines provide better restoring forces compared to the other materials and also the behavior of mooring system can be greatly affected with change in line diameter and fairlead slope.

Mooring line fatigue: A risk analysis for an SPM cage system

In recent years, the development of single-point mooring (SPM) cage systems has received much attention due to their eco-friendly features. However, natural disasters such as hurricanes and typhoons can cause severe damage to the integrity of net cage system. To avoid mooring system failure, selecting an appropriate breaking strength for mooring lines is becoming an important issue in marine aquaculture industry. This study evaluates the failure risk of a mooring line based on extended-period environmental loadings. Results indicate that the recommended replacement period of a polyester (PET) mooring line (diameter 38 mm) is about 6.55 years if the line's safety factor is 1. However, if the required safety factor increases to 1.5 (diameter 50 mm), then the replacement period extends to 23.81 years about six times that of original life. The fatigue failure probability for mooring lines in the service period is about 0.49 and 0.29 for safety factors of 1 and 1.5, respectively.

Coupled-dynamic analysis of floating structures with polyester mooring lines

A theory and numerical tool are developed for the coupled-dynamic analysis of a deepwater floating platform with polyester mooring lines. The formulas allow relatively large elongation and nonlinear stress–strain relationships, as typically observed in polyester fibers. The mooring-line dynamics are based on a rod theory and the finite element method (FEM), with the governing equations described in a generalized coordinate system. The original rod theory [Nordgren, R.P., 1974. On Computation of the Motion of Elastic Rods. Journal of Applied Mechanics, 41, 777–780] is generalized to allow larger elongation and nonlinear stress–strain relationship. The dynamic modulus of polyester is modeled following an empirical regression formula suggested by [Bosman, R.L.M., Hooker, J., 1999. The Elastic Modulus Characteristic of Polyester Mooring Ropes. In: Proceedings of the Offshore Technology Conference, OTC 10779. Houston, Texas], in which the axial stiffness is not constant, but depends on loading conditions. Two case studies, the static and dynamic behavior of a tensioned buoy and a classic spar with polyester mooring lines, are conducted. The time-domain simulation results are systematically compared with those from the original rod theory. The effects of large elongation and nonlinear stress–strain relations are separately assessed. It is seen that the mean offset, motions, and tension with polyester lines can be different from those by original rod theory with linear elastic lines.

Overview: Offshore Facilities: Construction and Design (February 2008)

Overview Deepwater and the Arctic, which, today, represent more than half of the world's undiscovered oil and gas resources, often are associated when it comes to the current challenges in exploration and production. But even if deepwater and the Arctic share a few common problems, those associated with arctic conditions present many unique specificities and a much wider range of technological issues. Among the reasons, arctic areas are interpreted as those with prevailing cold-climate conditions and include, in addition to the whole area north of the Arctic Circle, the subarctic regions down to northeast Canada, Sakhalin, and the Caspian Sea (just to name the more active ones). Also, arctic means not only offshore deep and shallow areas—sometimes including areas with many challenges for very shallow developments (e.g., Kashagan) and for all shore approaches—but also onshore, with long pipelines, large plants, and all the associated infrastructure (e.g., roads and buildings). Common features include high-technological content, heavy logistics, high sophistication of required equipment, and, certainly, high cost of development and production. In addition, subsea processing (separation, boosting, and compression) that enables solving deepwater flow-assurance issues and increasing recovery rates should bring the same advantages to Arctic production and ultimately, in some cases, could allow subsea-to-beach configurations, thus greatly reducing interaction with ice. Remoteness, personnel safety, and environmental footprint (already very important in deepwater) take an even more important place in the highly sensitive Arctic zones. Obvious unique specificities of the Arctic are those related to the low temperatures (i.e., ice, icing, and interaction of ice, ridges, and icebergs with structures and pipelines), leading to ice strengthening and/or disconnect-ability of structures, deep burial of pipelines, ice management for offshore developments, and (for both onshore and offshore) all the difficulties linked to the presence of permafrost. All of these concerns have common major uncertainties linked to the current situation, as well as to their evolution in the future. Even with all the unique challenges of the Arctic, these offshore developments will certainly benefit from the great experience that operators and contractors have already gained in the deepwater scene. However, developments in the Arctic will have to cope with even-more-difficult environmental challenges and larger uncertainties. Offshore Facilities: Construction and Design additional reading available at the OTC Library: www.otcnet.org OTC 18768 "Polyester Mooring Lines on Platforms and MODUs in Deep Water" by John F. Flory, Tension Technology International, et al. OTC 18903 "Development of Revised Gulf of Mexico Metocean Hurricane Conditions for Reference by API Recommended Practices" by E.P. Berek, ExxonMobil, et al.

Overview: Deepwater Exploration and Production (June 2007)

Offshore operators and contractors continue to accept and meet new deepwater challenges. As shown in the following articles, the apparent limits of deepwater technologies are extended every year, and new records and "firsts" are achieved to meet projects' increasingly ambitious requirements. Subjects covered this year include the first operational use of a new major equipment type, one of the first secondary-recovery projects in a deepwater environment, and two very different major deepwater projects. The projects and technologies described in the articles entail significant risks, and some of the articles discuss the risk management strategies used. The technical and commercial success of these projects depends on accurate risk assessment, risk mitigation strategies, and the continued progressive development of cutting-edge technologies. The use of new technologies, however, does not always result in increased risks. In some cases, technologies are devised to mitigate an identified risk, as indicated in the articles' discussions of "improved reliability," "enhancements in functionality," "optimization," "standard interfaces and interchangeability," "increased data quality," "improved durability," "improved facility uptime," and other key themes. Management of project risks is one of the most important tasks in project management. Rather than a one-off activity that is addressed only with a workshop facilitated by an outside expert and filed away, risk management should be an ongoing process that starts with project initiation and continues through the end of facility operation. Deepwater Exploration and Production additional reading available at the OTC Library: www.otcnet.org OTC 18768 "Polyester Mooring Lines on Platforms and MODUs in Deep Water," by John F. Flory, Tension Technology, et al. OTC 18493 "Extreme Wave Effects on Deepwater Floating Structures," by Bas Buchner, Maritime Research Institute Netherlands, et al. OTC 18797 "Combined Tow Method for Deepwater Pipeline and Riser Installation," by Alf Roger Hellestø, Subsea 7, et al. OTC 18844 "Special Session: AUVs: Groundtruthing High-Resolution AUV Side-Scan-Sonar Contacts for Unexploded Ordnance in a Deepwater GeoHazard Assessment," by Lynn B. Samuel, C&C Technologies, et al.

Wear and Fatigue of Nylon and Polyester Mooring Lines

Wear and fatigue in synthetic fiber lines depend on a multitude of mechanisms, including cumulative creep to rupture, hysteretic heating due to cyclic loading of filaments or to relative displacement of structural rope elements, internal wear caused by relative movement between yarns or strands, and external abrasion against deck hardware or rough surfaces. Studies undertaken to evaluate fiber, yarn, and rope responses to each of these mechanisms, singly or in combination, vary significantly with the test conditions including cyclic load level (both axial and transverse), cyclic strain level, and ambient conditions, i.e., temperature and moisture content (whether dry or wet in fresh water or salt). Cyclic load limits depend on wave height, wind velocity, and mooring line dimensions and properties. The relative durability of nylon versus polyester lines is considered as the lines are subjected to tensile cycling under storm conditions. While tensile fatigue as a creep phenomenon is operative over the free length of the mooring line, the more critical location of rope deterioration is at its interactive contact with deck hardware. An ideal mooring system is composed of two segments. The one between the elements of deck hardware (cleats and chocks) should possess maximum abrasion resistance and high tensile stiffness. The other segment should possess high tensile compliance so as to minimize cyclic load levels induced by waves and wind. A review of yarn/yarn wear tests and rope abrasion tests is provided to form the foundation for recommendations.