The Fracture Resistance Approach in Order to Prevent Brittle Failure of Offshore Structures Under Arctic Environments

2016 ◽  
Author(s):  
Agnes Marie Horn ◽  
Erling Østby ◽  
Per Olav Moslet ◽  
Mons Hauge
Keyword(s):  
Brittle Failure ◽  
Structural Integrity ◽  
Early Stage ◽  
Steel Structures ◽  
Offshore Structures ◽  
The Arctic ◽  
Design Stage ◽  
Main Question ◽  
Overall Design ◽  
Offshore Industry

This paper is concerned with the challenges related to steel design under Arctic conditions where both loading and temperature have been discussed in relation to material requirements. Today there is a lack of rules and standards for selecting steel materials for bulk engineering for a lower design temperature than −10°C (NORSOK N-004 [1] allows down to −14°C). Both ISO 19902 Steel Structures [2] and NORSOK N-004 Design of steel structures make reference to EN10225 “Weldable structural steels for fixed offshore structures technical delivery conditions [5]” where steel materials are Charpy tested at a lowest test temperature of −40°C and proven for a design of −10°C. Hence, one major challenge for designers are to specify adequate toughness requirements at an early stage of the design process for low temperature applications. Both NORSOK N-004[1] and ISO 19902[2] provide requirements to load combinations that need to be fulfilled, however the relationship between various load types and temperature is not mentioned in any of these standards. Thus, in the design stage the material needs to demonstrate adequate toughness where loading and temperature are treated independently. For the offshore industry, the main question is the balance between materials requirements and cost-effective solutions, and how to address this within an overall design perspective in order to avoid brittle failure. This paper discusses some of these challenges with the aim of starting a focused process leading up to a clear interpretation of the implications of overall design philosophies, necessary in order to define consistent materials requirements ensuring that brittle fracture is not going to represent a significant threat to the structural integrity. The material recommendations provided in the paper are based on the latest research results from the Arctic Materials project (2008–2017) managed by SINTEF and supported by the industry.

Design Under Arctic Conditions: A Summary of the Arctic Materials Project Guideline

2018 ◽  
Author(s):  
Agnes Marie Horn ◽  
Erling Østby ◽  
Odd Akselsen ◽  
Mons Hauge
Keyword(s):  
Cost Effective ◽  
Offshore Structures ◽  
International Standards ◽  
Hydrocarbon Exploration ◽  
Thickness Effect ◽  
The Arctic ◽  
Structural Elements ◽  
Practical Applications ◽  
Arctic Materials ◽  
Offshore Industry

The main goal of the 10 years Arctic Materials KMB project run by SINTEF (2008–2017) and supported by the industry is to establish criteria and solutions for safe and cost-effective application of materials for hydrocarbon exploration and production in arctic regions. The objective of the arctic materials project guideline (PG) is to assist designers to ensure safe and robust, yet cost-effective, design of offshore structures and structural elements in arctic areas through adequate material testing and requirements to material toughness. It is well known that when the temperature decreases, steel becomes more brittle. To prevent brittle fracture in the Arctic, the structure needs adequate toughness for the loading seen at low temperatures. None of the common offshore design codes today consistently address low temperature applications. In this respect, arctic areas are defined as minimum design temperatures below what current international standards have considered per today, i.e. −10 °C to −14°C. For practical applications, the PG defines arctic areas as minimum design temperature lower than −10 °C. It is acknowledging that design standards to a certain degree are based on operational and qualitative experiences gained by the offshore industry since the 1970’s. However, for arctic offshore facilities, limited operational experiences are gained by the industry. The basis of the guideline is that safe and robust design of structures and structural elements are ensured by combining standard industry practice today with learnings and findings from the 10 years Arctic Materials project. This paper is concerned with the rationale behind the material and test requirements provided in the arctic material guideline. The material requirements will be discussed in detail with emphasis on toughness requirement, constraint effect, thickness effect, acceptance criteria and material qualification criteria.

scholarly journals The Effect of Notch Depth on CTOD Values in Fracture Tests of Structural Steel Elements

2018 ◽  
Vol 25 (2) ◽  
pp. 85-91
Author(s):  
Jakub Kowalski ◽  
Janusz Kozak
Keyword(s):  
Brittle Fracture ◽  
Test Procedure ◽  
Charpy Impact ◽  
Steel Structures ◽  
Charpy Impact Test ◽  
Offshore Structures ◽  
The Arctic ◽  
Notch Depth ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement

Abstract In elements of steel structures working at low temperatures, there is a risk of appearance of brittle fracture. This risk is reduced through the use of certified materials having guaranteed strength at a given temperature. A method which is most frequently used to determine brittle fracture toughness is the Charpy impact test, preformed for a given temperature. For offshore structures intended to work in the arctic climate, the certifying institutions more and more often require Crack Tip Opening Displacement (CTOD) tests instead of conventional impact tests, especially for steel and welded joints of more than 40 mm in thickness in the case of high-strength steel, and more than 50 mm for the remaining steels. The geometry of specimens and the test procedure are standardised; however, these standards provide some margin for specimen notch depth. The paper analyses the effect of notch depth difference, within the range permitted by the standards, on the recorded CTOD values of a given material. The analysis was performed via numerical modelling of destruction of specimens with different notch geometries and further verification of the obtained numerical results in laboratory tests. The calculations were carried out at the Academic Computer Centre in Gdansk.

Sea spray icing: The physical process, and review of prediction models and winterization techniques

2021 ◽  
pp. 1-26
Author(s):  
Sujay Deshpande ◽  
Ane Sæterdal ◽  
Per-Arne Sundsbø
Keyword(s):  
Prediction Models ◽  
Offshore Structures ◽  
Cold Climate ◽  
Working Environment ◽  
The Arctic ◽  
Design Stage ◽  
Sea Spray ◽  
Ice Accretion ◽  
Sea Wind ◽  
The Impact

Abstract Ice accretion on marine vessels and offshore structures is a severe hazard in the Polar Regions. There is increasing activities related to oil and gas exploration, tourism, cargo transport, and fishing in the Arctic. Ice accretion can cause vessel instability, excess load on marine structures and represents a safety risk for outdoor working environment and operations. Freezing sea spray is the main contributor to marine icing. For safe operations in cold climate, it is essential to have verified models for prediction of icing. Sea spray icing forecast models have improved. Empirical and theoretical models providing icing rates based may be useful as guidelines. For predicting the distribution of icing on a surface at the design stage, Computational Fluid Dynamics has to be applied along with a freezing module. State-of-the-art models for numerical simulation of sea spray icing are still not fully capable of modelling complex ship-sea-wind interactions with spray generation and impact of shipped water. Existing models include good understanding of spray flow effects and freezing. Further development should focus on developing models for dynamic ship-sea-wind interactions, in particular including spray generation, effects of shipped water and distribution of icing on the vessel surface. More experimental and full-scale data is needed for development and verification of new and improved models. Models that estimate ice distribution may improve the winterization design process and reduce effort required for de-icing. Improved methods for de-icing and anti-icing will reduce the impact of sea spray icing and increase safety for marine operations in cold waters.

Reliability and (Re)Assessment of Fixed Steel Structures

2011 ◽  
Author(s):  
Mike Efthymiou ◽  
Jan Willem van de Graaf
Keyword(s):  
Structural Reliability ◽  
Structural Integrity ◽  
Steel Structures ◽  
Performance Standards ◽  
Offshore Structures ◽  
Design Standards ◽  
Component Strength ◽  
Post Buckling ◽  
Exposure Levels ◽  
Joint Occurrence

This paper reviews the structural integrity and reliability of fixed steel offshore structures with a focus on improved models and incorporation of these models in design standards. Technical achievements in four key areas are reviewed which, when combined, resulted in a step improvement in the calculation of structural reliability. The first area is the extreme environmental loading on an offshore platform; the second area is the joint occurrence of waves, winds and currents, i.e. accounting for the fact that these do not, in general, peak at the same time and do not act in the same direction. The third area is the estimation of the ultimate strength of a fixed steel platform, accounting for component strength, including the buckling and post-buckling behaviour and the uncertainty in system strength. The fourth and final area is the integration of the above models to estimate the probability of failure. The historical performance of platforms and the improvements in successive editions of API RP 2A are reviewed; reliability targets appropriate for different exposure levels and corresponding performance standards are developed, aimed at harmonizing design practices worldwide. A differentiation is recommended between permanently manned L-1 installations and manned-evacuated L-1 installations in the Gulf of Mexico; this is because the consequences of failure are considerably different.

Structural Integrity Management Framework for Fixed Jacket Structures

2008 ◽  
Author(s):  
A. Stacey ◽  
M. Birkinshaw ◽  
J. V. Sharp ◽  
P. May
Keyword(s):  
Structural Integrity ◽  
Good Practice ◽  
Offshore Structures ◽  
Management Framework ◽  
Offshore Installations ◽  
Jacket Structures ◽  
Integrity Management ◽  
Offshore Industry

In recent years, a significant amount of effort has been expended by HSE and the offshore industry on the development of good practice for structural integrity management in the new code for offshore structures, ISO 19902. However, a review of the structural integrity management of fixed offshore installations operated on the UKCS has indicated that duty holders adopt varying approaches, in terms of both the methods used and effectiveness. The elements of a framework for the management of the structural integrity of fixed jacket structures are presented.

Practical Application of Global Optimization to the Design of Offshore Structures

2004 ◽  
Author(s):  
Lothar Birk ◽  
Gu¨nther F. Clauss ◽  
June Y. Lee
Keyword(s):  
Global Optimization ◽  
Optimization Algorithms ◽  
Computation Time ◽  
Offshore Structures ◽  
Deterministic Algorithm ◽  
Assessment Tools ◽  
Design Stage ◽  
Overall Design ◽  
Hull Design ◽  
Quadratic Programming Method

The paper presents improved methods and new results on the introduction of formal optimization strategies into the design of offshore structures. The hull design stage is singled out from the overall design process and automated by introducing parametric shape generation, numeric hydrodynamic analysis and assessment tools as well as Nonlinear Programming algorithms for process control. The investigation compares the performance of three different optimization algorithms within a shape optimization framework. The classical deterministic Sequential Quadratic Programming method competes with two so called global optimization algorithms: The popular Genetic Algorithm and the more exotic Adaptive Simulated Annealing. The applications show that significant improvements of seakeeping qualities are obtained in either case. As expected, the global methods require definitely more computation time than the deterministic algorithm. Furthermore the global methods do not always produce better results, which makes a careful choice of the optimization algorithm mandatory. Guidelines for an efficient application are given in the conclusions.

Evaluation of Loads During a Free-Fall Lifeboat Drop

2013 ◽  
Author(s):  
Andrea Califano ◽  
Kristoffer Brinchmann
Keyword(s):  
Finite Element ◽  
Structural Integrity ◽  
Early Stage ◽  
Free Fall ◽  
Element Model ◽  
Emergency Evacuation ◽  
Offshore Structures ◽  
Element Analysis ◽  
Safety Requirements ◽  
Structural Capacity

A new Offshore Standard (DNV-OS-E406) [1] has been developed for the design of Free Fall Lifeboats (FFLB) used for emergency evacuation from offshore structures. This standard aims at ensuring safe evacuation, focusing on the design at an early stage. Load (CFD) and structural (FE) analyses are used to assist in determining whether or not the free fall lifeboats comply with the Target Safety requirements as set forth by the Standard. The present paper describes the methodology used when assessing the structural capacity of FFLB. The structural integrity is established throughout every phase of a lifeboat drop, linking computational fluid dynamics (CFD) and finite element analysis (FEA). Loads computed from CFD on a finite volume mesh are interpolated to a finite element model where the structural analysis can be performed in order to obtain stresses, strains and deflections, and finally assess the structural capacity of the lifeboat. Emphasis in this work is given to the hydrodynamic model and loads, while structural analyses are discussed more in depth by Brinchmann et al. [2].

Evaluation of the Ice Load Acting on an Arctic Offshore Structure With Different Ice Drifting Angle

2020 ◽  
Author(s):  
Young-Shik Kim ◽  
Yun-Ho Kim ◽  
Hyung-Do Song ◽  
Jin-Ho Jang ◽  
Solyoung Han ◽  
...  
Keyword(s):  
Evaluation Method ◽  
Offshore Structures ◽  
Mean Value ◽  
Experimental Methodology ◽  
The Arctic ◽  
Design Stage ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Ice Load ◽  
National University

Abstract In this study, an evaluation method and results for ice load acting on an Arctic offshore structure with various ice drifting angles are discussed. Korea Research Institute of Ships and Ocean Engineering (KRISO) has conducted a research project to develop a hull form design for year-round floating type offshore structures in the Arctic condition with dynamic positioning and mooring system. Six cooperating organizations participated in the project: Samsung Heavy Industry, Korean Register, Pusan National University, Korea Maritime & Ocean University, Dong-Eui University, and Inha Technical College. In the design stage of an Arctic offshore structure, ice load consideration is the key component for the safety and reliability analysis. However, there is no generally used tool for evaluation of ice load acting on an Arctic offshore structures. In this study, ice loads acting on an Arctic FPSO in managed ice conditions with various ice drifting angles are examined by experimental methodology. Dramatic mean value changes in ice load with different ice drifting angles are observed in the model test. This experimental ice load evaluation method can be applied to the other types of offshore structure which might operate in sea ice condition.

Fatigue Analysis of Offshore Structures

1979 ◽  
Vol 101 (4) ◽  
pp. 218-224
Author(s):  
J. R. Wallis ◽  
Y. O. Bayazitoglu ◽  
A. Mangiavacchi ◽  
F. M. Chapman
Keyword(s):  
Rayleigh Distribution ◽  
Offshore Structures ◽  
Fatigue Analysis ◽  
Energy Spectra ◽  
Wave Loads ◽  
Sea Waves ◽  
Design Procedures ◽  
Overall Design ◽  
Forcing Function ◽  
Offshore Industry

As the offshore industry moves into deeper water, the dynamic behavior of structures becomes a very important parameter in the overall design procedures. In particular, the cyclic nature of wave loads has a significant effect on the fatigue life of the structure. This paper presents a procedure for fatigue analysis where the dynamic response of the structure is analyzed through a spectral approach. The sea waves which constitute the forcing function acting on the structure are represented as energy spectra; the response is obtained in spectral terms and is subsequently interpreted according to probabilistic concepts. As part of this study we have considered the characteristics of the distribution of the response. In the usual approach to fatigue analysis one assumes that the peaks of the response follow a Rayleigh distribution. This assumption is valid if the Cartwright-Longuet-Higgins’ measure of bandwidth (ε) is equal to zero. However, in practical fatigue applications, this idealization is rarely, if ever, encountered. Thus, in order to better characterize narrow-banded phenomena, we have investigated descriptions which do not assume ε = 0. An investigation of caisson designs indicates that fatigue using the more accurate response distributions can differ appreciably from those obtained with the Rayleigh distribution.

Tailoring Design Development and Ideation in Catering To Industry Demands

2017 ◽  
Vol 14 (1) ◽  
pp. 67
Author(s):  
Fadila Mohd Yusof ◽  
Azmir Mamat Nawi ◽  
Azhari Md Hashim ◽  
Ahmad Fazlan Ahmad Zamri ◽  
Abu Hanifa Ab Hamid ◽  
...  
Keyword(s):  
Teaching And Learning ◽  
Industrial Design ◽  
Protocol Analysis ◽  
Early Stage ◽  
Idea Generation ◽  
Learning Processes ◽  
Design Stage ◽  
Design Development ◽  
Conceptual Design Phase ◽  
Industry Practice

Design development is one of the processes in the teaching and learning of industrial design. This process is important during the early stage of ideas before continuing to the next design stage. This study was conducted to investigate the comparison between  academic  syllabus  and  industry  practices  whether  these  processes  are  highly dependent on the idea generation and interaction related to the designer or to the student itself. The data were gathered through an observation of industry practice during conceptual design phase, teaching and learning process in academic through Video Protocol Analysis (VPA) method and interviews with industry practitioners via structured and unstructured questionnaires. The data were analysed by using NVivo software in order to formulate the results. The findings may possibly contribute to the teaching and learning processes especially in the improvement of industrial design syllabus in order to meet the industry demands. Keywords: design development, industrial design, industry demands

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