Correlation of microstructure and fracture properties of API X70 pipeline steels
- PDF / 1,594,722 Bytes
- 15 Pages / 612 x 792 pts (letter) Page_size
- 104 Downloads / 236 Views
I. INTRODUCTION
HIGH-STRENGTH pipeline steels make great contributions to energy conservation and cost reduction as well as to increased transportation efficiency, as they allow transportation of crude oil and natural gas under high pressure.[1–5] However, as high strength is generally achieved at the expense of reduced toughness and ductility, it is imperative to ensure the reliability of high-strength pipeline steels for their structural integrity in order to operate and maintain them stably over a long period of time. Particularly, fracture toughness obtained from Charpy impact tests and dropweight tear tests (DWTTs) is one of the most critical factors in guaranteeing the structural integrity of pipeline steels.[6–15] Technologies to prevent the fracture of pipeline steels can be largely explained in terms of fracture initiation and fracture propagation.[10] The fracture initiation refers to when flaws resulting from mechanical damages, e.g., notch, crack, dent, and gouge, or corrosion,[8,9] e.g., hydrogen-induced cracks and sulfide stress corrosion cracks, reach a critical length or a certain stress level and start to propagate. Major factors involved in this stage are the size and orientation of flaws, diameter and thickness of pipes, toughness, temperature, and fluid. On the other hand, the fracture propagation is largely dependent on the correlation between the fracture
BYOUNGCHUL HWANG, Postdoctoral Research Associate, and YOUNG MIN KIM, Research Assistant, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784 Korea. SUNGHAK LEE and NACK J. KIM, Professors, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, are jointly appointed with the Materials Science and Engineering Department, Pohang University of Science and Technology. Contact e-mail: [email protected] SEONG SOO AHN, Researcher, is with the Plate Research Group, Technical Research Laboratories, POSCO, Pohang, 790-785 Korea. Manuscript submitted February 16, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
velocity of pipes and the decompression velocity of gas, and is affected by factors such as fracture mode, temperature, pressure, diameter, and thickness of pipes, yield strength, toughness, surrounding environment, applied stress, and compressed fluid. In the perspective of the fracture initiation, it is critical to prevent leaks from pipelines by making steels tougher and by controlling the size and shape of flaws. In terms of the fracture propagation, it is important to delay abrupt fracture propagation by making steels tougher so that immediate repairs may be done, even if serious flaws were introduced into pipelines. Consequently, practical fracture control technologies should take consideration of both aspects of fracture initiation and fracture propagation in balance. Many engineers have been deeply involved in developing ways to predict fracture in pipeline steels by formulating the relation between the aforementioned factors and material pr
Data Loading...
