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Results
Determination of Ccrystallographic Facet Orientations On Fracture Surfaces of an Arctic Steel By Using EBSD
Mohseni, Peyman (Norwegian University of Science and Technology (NTNU)) | Solberg, Jan Ketil (Norwegian University of Science and Technology (NTNU)) | Karlsen, Morten (Norwegian University of Science and Technology (NTNU), and Statoil ASA) | Akselsen, Odd M. (Norwegian University of Science and Technology (NTNU), and SINTEF) | Østby, Erling (SINTEF)
ABSTRACT Electron backscatter diffraction (EBSD) has been increasingly used to identify the crystallographic planes and orientation of cleavage facets with respect to the rolling direction in fracture surfaces. The crystallographic indices of cleavage planes can be determined either directly from the fracture surface or indirectly from metallographic sections perpendicular to the plane of the fracture surface. The commonly observed crystallographic mode (i.e. the micromechanism) of brittle fracture in ferritic steels is cleavage, which involves the separation of atomic bonds along low-index {100} crystallographic planes. The main purpose of this work was to identify the crystallographic orientations of cleavage facets in fracture surfaces with respect to the rolling direction of a well known steel at low temperatures. The material used for the work was a steel (API X80 grade) that has been developed for applications at low temperatures. The crystallographic indices of the cleavage crack planes were identified to be {100}, {110}, {211} and {310} at all temperatures. INTRODUCTION High strength and toughness pipeline steels have been used at high operation pressures to improve the transport efficiency of oil and gas. The major motivation behind the development of such steels has been to obtain the best combination of strength and toughness (Bose-Filho, Carvalho, Strangwood, 2007). Weldability, high fracture toughness and fatigue resistance at low temperatures are additional requirements for transmission of oil and gas through pipelines (Das, Sivaprasad, Dasa, Chatterjee and Tarafder, 2006). The balance of high strength and high toughness can be deteriorated by welding thermal cycles, producing local poor toughness in the welded joints (Lambert-Perlade, Gourgues, Besson, Sturel, and Pineau, 2004, Davis and King, 1996). The heat affected zone (HAZ) is in many cases considered to be the most critical part of a weld. The region of lowest toughness after single pass welding is the coarse grained heat affected zone (CGHAZ) (Qiu, Mori, Enoki and Kishi (2000) and Akselsen, Solberg and Grong, 1988).
- Energy > Oil & Gas (1.00)
- Materials > Metals & Mining > Steel (0.48)
Application of Electron Backscatter Diffraction (EBSD) On Facet Crystallographic Orientation Studies In Arctic Steels
Mohseni, Peyman (Norwegian University of Science and Technology (NTNU)) | Solberg, Jan Ketil (Norwegian University of Science and Technology (NTNU)) | Østby, Erling (SINTEF) | Akselsen, Odd Magne (Norwegian University of Sceince and Technology (NTNU), SINTEF)
ABSTRACT: Thick-walled high strength line pipes are being increasingly used for high-pressure pipeline operations to improve the transport efficiency for natural gas and oil. As an added challenge, pipeline construction for natural gas and oil transport is sometimes taking place in severe environments such as in the Arctic. Thus, the line pipe must have lowtemperature toughness together with high tensile properties. In this work, a study of the relationship between the brittle to ductile transition temperature and the microstructure in HAZ was carried out by applying resistant heating weld simulation. The main purpose of the work was to identify the crystallographic orientation of the cleavage facets in the fracture surface with respect to the rolling direction of the steel. The application of electron backscatter diffraction (EBSD) provided a method for investigating the crystallography of the fracture facets. The results reveal that the crystallographic indices of the cleavage crack planes were identified to be (001), (110), (211) and (310). INTRODUCTION High strength low alloy steels are used for high pressure pipeline operations to improve the transport efficiency. Pipeline steels, used for transporting natural gas and oil over a long distance, become stronger, tougher, larger, and thicker for cost reduction and high pressure transportation. The pipeline construction is sometimes taking place in severe environments such as in the Arctic. Thus, the demand for higher strength and toughness in pipeline steels has increased (Bose-Filho, Carvalho, Strangwood 2007; Das, Sivaprasad, Dasa, Chatterjee and Tarafder, 2006). HSLA steels combine excellent tensile strength and ductile-to-brittle transition (DBT) properties. However, this combination of high strength and high fracture toughness can be deteriorated by welding thermal cycles. The degradation of the fracture toughness of HSLA steels after welding is attributed to the formation of "local brittle zones" in the welded joint (Lambert-Perlade, Gourgues, Besson, Sturel, and Pineau, 2004).
- Materials > Metals & Mining > Steel (1.00)
- Energy > Oil & Gas (1.00)