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Collaborating Authors
Østby, Erling
ABSTRACT The potential role of hydrogen as an important energy carrier in the new energy mix is receiving a lot of attention. The option of transporting hydrogen in pipelines is highly relevant in this respect. At the same time, it is known that hydrogen may have a detrimental effect on steel properties, which could pose restrictions in design of such pipelines. Currently, some experience exists when it comes to transporting hydrogen in onshore pipelines, and some codes (e.g. ASME B31.12) have been developed to provide guidelines on design. There is an interest to also develop projects including offshore pipelines for H2 transport. Offshore pipelines pose some new design challenges, e.g. higher axial loads (both cyclic and static) and typically higher pressures. As a response to these challenges DNV has launched the H2Pipe Joint Industry Project with an objective to develop a guideline for design and potential re-purposing of offshore pipelines for H2 transport. This paper gives a status summary of the guideline work in the JIP and presents results from mechanical testing performed in Phase 1 of the JIP. INTRODUCTION Hydrogen is assumed to be an important part of tomorrow's energy mix. C-Mn pipelines are considered a highly relevant means of transporting H2 gas in this respect. The recently increased interest is likely due to that it in addition to transporting energy may also be used for storing energy. Both design of new and re-purposing of existing pipelines are relevant scenarios. At the same time, it is well known that hydrogen may have a detrimental effect on the properties of steels, resulting in what is often termed "hydrogen embrittlement" (HE). HE might lead to significantly reduced ductility in steels. In addition to reduction in ductility, it is also likely that hydrogen leads to increased susceptibility under fatigue loading as well as a decrease in fracture resistance. It is necessary to have a sufficiently detailed knowledge on the magnitude of these effects in order to allow for safe yet cost-effective pipeline solution for transport of H2. Despite having been known for about 150 years, there are still significant uncertainties regarding the actual mechanisms controlling HE. There is already some experience with H2 transport in onshore pipelines. Further, guidance regarding design of such can be found in ASME B31.12 and IGEM/TD/1. However, offshore transport of H2 is also a relevant scenario, and no experience exists in this respect. Offshore pipelines offer some additional challenges like more cyclic loading, larger operational loads, and special accidental loading scenarios. In order to address these challenges DNV has launched the H2Pipe JIP with the ambition to provide guidelines for design and re-purposing of C-Mn pipelines for offshore H2 transport. The focus of the paper will be towards structural integrity issues of H2 pipelines while flow and transport capacity issues will not be addressed. First limit states and special challenges for offshore pipelines are discussed. Then a brief outline of HE is presented together with a short summary of existing codes for design of H2 pipelines. This is followed by a presentation of key experimental findings from Phase 1 of the JIP and an outline of the current status of the Guideline document. The paper is concluded with a general discussion and key conclusions. Phase 1 of the JIP was concluded early in 2023 and a Phase 2 of the JIP was kicked off in early 2023 with the objective to close some of the main gaps identified in this paper.
ABSTRACT In recent years several incidents related to failures of high strength mooring chains used in mobile offshore units mooring systems have been reported. Investigations of some of these incidents have been carried out by, or on behalf of, the chain owner, the rig owner or the operator involved, resulting in a set of explanations for why they occurred. As a result, a set of possible measures to counteract them have been launched. In this paper a systematic review of the available data is made and discussed, and some conclusions on the possible root causes and failure mechanism for the failures are presented. A gap analysis on the specific material knowledge was performed and the resulting suggested research and test program is presented. INTRODUCTION Higher strength material mooring chains have become widespread for offshore mobile units mooring systems on the Norwegian Continental Shelf (NCS) and are expected to be essential for the viability of Floating Offshore Wind Turbine (FOWT) installations. The high failure rate observed in some productions of R5 grade material has resulted in dedicated investigations and actions across the industry (Barros et al., 2022). The failures considered in this paper occurred in chain which were fully compliant with the existing standards. It is observed however, that an apparent heightened sensitivity to hydrogen cracking which associated with surface damages caused by handling of the chain onshore and offshore, in combination with high load events and CP exposure, has resulted in the reported failures. Mitigation actions have been implemented mainly focusing on reducing damages from handling and high load events, but a more refined and clear criteria to properly certify high strength material mooring chains needs to be established A research and testing program is proposed and described with the aim of confirming the identified root causes and failure mechanism and to provide quantitative background for the mitigation actions implemented. MATERIALS AND METHODS The information presented in this paper has been obtained from the available failure investigation reports, bibliographic review, presentations at seminars, workshops and interviews with different industry players. Chain manufacturers, chain rental companies, anchor handling operators, rig owners and license owners have been consulted.
Hydrogen Transport in Offshore Pipelines – Identified Need for Code Extensions
Collberg, Leif (DNV) | Leinum, Bente (DNV) | Helgaker, Jan Fredrik (DNV) | Hugaas, Bjørn-Andreas (DNV) | Østby, Erling (DNV) | Levold, Erik (Equinor) | Strømme, Per Atle (Gassco)
Abstract The energy transition from hydrocarbon-based energy to renewable is progressing rapidly. The transition speed has experienced ups and downs but has recently seen a boost and there are clear indications that the speed will accelerate considerably over the next 5-10 years. This transition and a possible future change in the European gas market has triggered several stakeholders to investigate the possibility for export of hydrogen gas as an addition or replacement for natural gas. In this context, both the design, fabrication and installation of new pipelines as well as utilisation of existing gas export infrastructure is on the agenda. A large-scale deployment of pipelines for hydrogen transport, however, requires that the best possible balance between safety and cost-effectiveness can be established to allow for optimal design of new pipelines, or possibly assessment of the use of existing pipeline infrastructures. There is today no offshore pipeline code covering hydrogen transport or mix of hydrogen. A new revision of ASME B31.12 [1] design code was issued in 2019. This new revision may reduce the conservatism for transporting hydrogen, however, it lacks offshore specific design issues. A study has been performed on behalf of Equinor and Gassco to evaluate and identify gaps for offshore applications as reflected in DNVGL-ST-F101 [2] that either needs to be updated or re-formulated in case of hydrogen transport. The focus of this paper will be on the structural side, but considerations on flow (pressure, speed, impurities), safety (leakage, dispersion, accidents), materials and operation (repair, inspections) are also covered. The main impact from hydrogen is assumed to be on fracture propagation and toughness. The main limit states were evaluated on this basis and modifications proposed. The intention is to publish the results in a recommended practice as complement to the already existing DNVGL-ST-F101 [2] for offshore pipelines. Introduction As recently as three years ago, clean hydrogen energy was on the fringes of the energy-transition conversation – an outlier solution, at least for the short or medium term. Today, it is rapidly moving into the mainstream and, for many, it is essential to a net-zero energy future.
- Health, Safety, Environment & Sustainability > Sustainability/Social Responsibility > Sustainable development (1.00)
- Health, Safety, Environment & Sustainability > Environment > Climate change (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Offshore pipelines (1.00)
Abstract This state-of-the-art paper is devoted to testing and evaluation of microstructural crack arrest. Testing and analysis of crack arrest have developed in the last decades, enhancing our understanding of the mechanisms behind crack arrest in a continuum mechanics perspective. Understanding crack arrest is important when operations are moving towards Arctic regions as low temperatures are detrimental to most steel's fracture toughness. Large-scale testing is expensive and unpractical, and current methods fail to reflect the microstructural and micromechanical features of the fracture process. In order to increase the effectiveness of characterizing crack arrest properties, small-scale tests, as well as numerical methods, have been developed. The mechanical basis and mechanisms behind crack arrest are presented. Global and micro-arrest is considered. Key methods for understanding, evaluating and obtaining arrest parameters are presented:statistical treatment of experimental results, barrier models for separating fracture and arrest sequences, and numerical tools for determining arrest behaviour. Brief presentations of the main mechanisms of crack arrest are presented with focus on the micromechanisms of arrest. The effect of grain boundaries, lattice orientation and second-phase particles upon propagation controlled cleavage are discussed, as well as their role in the arrest mechanism. Developments in arrest testing and evaluation are presented. Experimentally and numerically obtained results are linked to relevant mechanisms and theory, exhibiting the predictability and importance of crack arrest properties, and the understanding of the governing mechanisms behind crack arrest. The potential for increased understanding of the brittle fracture arrest phenomenon associated with new methods for nanomechanical testing of the material properties inside individual grains, and over grain boundaries, as well as the rapidly improving capabilities of atomistic modelling of deformation and fracture, is presented to pave the way for the future research within this field. Areas where further research could enhance our knowledge of crack arrest are listed. Introduction Crack arrest is considering running cracks that are halted due to increasing resistance to crack propagation and/or reduced crack driving force. The former may be due to microstructural barriers or thermal gradients in the material. The latter may occur under partly displacement controlled loading, where the crack extension may increase the compliance of the structure and reduce the local crack driving force, or as a result of dynamic effects caused by impact loading or stress oscillations in the structure. This paper is mainly concerned with aspects related to the material's resistance to crack propagation, i.e. the arrest toughness. Further, crack propagation is assumed to be dominated by cleavage fracture, i.e. ductile fracture and fatigue are not considered. The relative importance of these factors depends on the scale of which the arrest is considered. Further, the arrest can also be considered for different scenarios ranging from arrest of single grain sized microcracks up to arrest of macroscopic cracks on in the centimeter to meter range. In the first group the arrest happens locally, probably highly influenced by local microstructural features like grain boundary orientation, and would rather be categorized as avoidance of cleavage initiation on the macroscopic scale. In the latter group the problem is more of a conventional engineering fracture mechanics issue, ideally assessed through knowledge or measurements of the macroscopic arrest toughness, Kia. Ultimately, the two groups are part of the same problem, and there is a research aim to establish quantitative relations at different scales in orderto arrive at a general treatment of the problem.
- Research Report > New Finding (0.46)
- Overview > Innovation (0.34)
Status Update of ISO TC67/SC8/WG5: Materials for Arctic Applications
Hauge, Mons (Statoil) | Maier, Mark (Shell Global Solutions International BV) | Walters, Carey L. (Structural Dynamics, TNO) | Østby, Erling (Det Norske Vertias, AS) | Kordonets, Sergei M. (Hull department, Head Office of Russian Maritime Register of Shipping) | Zanfir, Christian (Office of Public Safety, CWB) | Osvoll, Harald (FORCE Technology Norway AS)
Gaps Identified by Barents2020 An ISO subcommittee was set up in 2011 to improve the existing Barents2020 was a four-year project with primarily Russian and standards and norms with respect to arctic offshore operations for the Norwegian partners that worked to harmonize requirements between petroleum, petrochemical, and natural gas industries. Within this the two countries for safe exploration and exploitation of oil and gas subcommittee, a specific working group was established to address the resources in the Barents Sea. Their project resulted in a number of application of materials in the environment of the arctic and cold recommendations to classification and standardization bodies and the regions. The work is focusing on a number of specific aspects related to identification of gaps in existing norms and standards.
- Europe > Netherlands (0.28)
- North America > United States (0.28)
C. The pre-cracked specimens had typically Assessing the Acceptability of Flaws in Metallic Structures a 20-50 "Cleavage initiation in the be explained by the observation in previous investigations where we intercritically reheated coarse-grained heat-affected zone: Part I. have revealed the existence of two types of microstructures, one Fractographic evidence", Metall. "Cleavage initiation in the martensitic/bainitic in CGHAZ), and the other in propagation intercritically reheated coarse-grained heat affected zone: Part II. It should be noted that Failure criteria and statistical effects", Metall. Trans., according to Eq. 1, which is based on empirical data from mainly base Vol.27A, pp 3019-3029. R. W. Hertzberg, Deformation and fracture mechanics of engineering Further studies and more instrumented Charpy tests are needed to materials vol.
Abstract This paper discusses the role played by FEA (Finite Element Analysis) in the development of basic understanding and procedures for the use in association with strain-based fracture assessments of pipelines. The basic fracture mechanics parameters and their assumptions are briefly presented and special challenges and possible limitations with respect to applications in large plastic strain scenarios are identified. The motivation for use of FEA in solving some of these challenges is discussed from different perspectives. A series of examples, although not claimed to be exhaustive, of the use of FEA in relation to strain-based facture assessment of pipelines is included to give a representative picture of the state of the art. The relation to general codes is also discussed, and the current lack of clear guidance on how to carry out such analyses is highlighted. The paper concludes with some perspectives regarding further development of the field, and some possible general steps are proposed in this respect.
- Research Report (0.66)
- Overview (0.46)
ABSTRACT The previous paper studied the effect of the internal stress distribution in specimen thickness on CTOD. The critical CTOD tends to decrease in consequence of the internal stress distribution in specimen thickness in case that secondary stress is tension mode toward the crack. In estimating the critical CTOD to brittle fracture in structural component with large residual stress distribution, it is important to take account of that secondary stress effect. This paper presents the effect of weld residual stress on critical CTOD to brittle fracture at lower shelf temperature of standard fracture toughness test. Using SENB and SENT specimens with / without residual stress, the fracture toughness tests have been conducted at -60°C. The effect of weld residual stress on critical CTOD to brittle fracture depends on critical CTOD level. The critical CTOD with residual stress is calculated by the superposition of δ or stress intensity factor based on Dugdale model. Moreover, the δ on secondary stress derived from residual stress field scarcely affects constraint loss correction because the stress field from residual stress falls within the small scale yield condition.
- North America > United States (0.28)
- Asia > Japan (0.28)
ABSTRACT Acoustic emission (AE) is used to monitor cleavage microcracking activity in weld thermal simulated HAZ microstructures of a 420 MPa rolled plate. Fracture mechanics testing at different temperatures is carried out for three different simulated HAZ microstructures: ICCGHAZ Δt8/5=15 s, CGHAZ Δt8/5=5 s, and ICCGHAZ Δt8/5=5 s. Two parameters are extracted from the AE measurements: the rate of microcrack nucleation and the distribution of arrested cleavage microcrack sizes. The latter is obtained based on a first-order relationship between microcrack sizes and AE signal amplitude, earlier established by the authors. The results are discussed in terms of the effects of temperature and microstructure. It is shown that on average the arrested microcrack sizes are smaller in the microstructures with faster cooling rate, i.e. with smaller prior austenite grain size. It is also demonstrated that the effect of temperature on the microcrack nucleation rate depends on the microstructure. Further, it is shown that a rapid increase in fracture toughness with temperature is usually associated with a significant reduction in the microcrack nucleation rate. The results are interesting both in terms of understanding the temperature effects on fracture toughness and also as input to development of micromechanical models for cleavage fracture.
- North America > United States (0.28)
- Europe > Norway (0.28)
- Energy > Oil & Gas (1.00)
- Materials > Metals & Mining > Steel (0.46)
ABSTRACT In the North Sea oil and gas installations, steel castings have been used for many decades. Here, high strength steel castings offer the chance to manufacture complex heavy-lift and fatigue-critical components for larger offshore structures without increasing the weight of the components or platforms. However, when the activities are moving north to colder climates, current existing castings may fail to meet the toughness requirements, and there is very limited information available on behaviour of weldments of castings under such extreme conditions. Therefore, the present investigation was carried out addressing the low temperature toughness of high nickel (~1.5% Ni) steel casting with 460 MPa yield strength. Preliminary welding trials were performed with flux-cored arc welding (FCAW) with an overmatch in weld metal strength. Both Charpy V notch impact and CTOD fracture mechanical testing were included at ?60°C. The results show that the Charpy V notch toughness is excellent at -60°C (> 100 J). The fusion line CTOD fracture toughness showed low values for the SENB05 samples, while SENB02 gave higher values. For both geometries, the lowest values were connected with pop-in events. The weld metal fracture toughness was satisfactory with the lowest value of 0.28 mm.