Papers by Keyword: Pipeline Steel

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Authors: H.S. Park, J.S. Kang, J.Y. Yoo, Chan Gyung Park
Abstract: Low carbon (~0.34 at.%) pipeline steels with high strength and high toughness are widely used for the transportation of petroleum and natural gas. These pipelines usually experience UOE (bending by U press, forming by O press, Expansion) piping followed by coating process at 250°C, which usually cause strain aging phenomenon with discontinuous yielding in service. In order to understand the major cause of the strain aging in these low carbon pipeline steels, the dislocations associated with solute carbon atoms have been investigated in three different types of steels (plate, pipe, and coated pipe). In-situ TEM heating up to 250°C for 30min did not cause any change of structure in both steel plate and pipe. However, APT results revealed the segregation of carbon atoms alone dislocation lines in ferrite region of both UOE pipes and coated pipes. It is believed that this solute segregation along the dislocations is the major cause in the case of strain aging of low carbon pipeline steels.
122
Authors: De Liang Ren, Bo Liao, Changling Xu, Lianhai Hu, Fu Ren Xiao
Abstract: By using the mathematical uniform design, a new agglomerated flux for high speed and multi-arc submerged arc welding (SAW) has been developed in this paper, which performs excellently in welding process, and the effects of flux composition on the welding characteristics is analyzed as well. The mechanical tests show that the weld metal obtained in SAW with this flux exhibits high toughness at low temperature, and the other mechanical properties of the weld metal also satisfy the technical specifications for the West to East Pipeline Project in China. The microstructures of the weld metal are also examined. Both optical and TEM microphotoes demonstrate that the weld consists mainly of small-sized and uniformly distributed acicular ferrite. These microstructures can effectively prevent the initiation and propagation of micro cracks, resulting in high notch toughness of the weld metal at low temperature.
405
Authors: Laura Vergani, Giorgia Gobbi, Chiara Colombo
Abstract: Pipeline working environment is characterised by corrosive conditions, able to develop hydrogen formation. The presence of atomic hydrogen localized in correspondence of crack tip, where the plastic strain reaches the maximum value, is responsible for life reduction. For this reason, it is important to estimate and predict the mechanical properties decay, in terms of toughness and crack propagation, when steel is in contact with hydrogen. Aim of this study is to develop FE models of two carbon, low-alloyed steels used in pipelines applications: X65 and F22. A complex model including three simulations steps is presented. It considers the combined effect of plastic strain and hydrogen concentration on the material toughness. The results of the model are validated by a comparison with experimental tests carried out on the two low-alloyed steel.
513
Authors: S.S. Ayvar, S.H. Hashemi, I.C. Howard, J.R. Yates
Abstract: This paper reports recent results from a set of experimental and computational studies of ductile flat fracture in modern gas pipeline steel. Experimental data from plain and notched cylindrical tensile bars and standard C(T) specimens together with damage mechanics theories have been used to capture the flat fracture characteristics of a gas pipeline steel of grade X100. The modelling was via finite element analysis using the Gurson-Tvergaard modified model (GTN) of ductile damage development. The assumption of effective material damage isotropy was sufficiently accurate to allow the transfer of data from the notched bars to predict, in a 2D model, the crack growth behaviour of the C(T) specimen. This was in spite of the considerable ovalisation of the bars at the end of their deformation. However, it was not possible to obtain similar accuracy with a 3D model of the C(T)test, even after a large number of attempts to adjust the values of the GTN parameters. This, and the anisotropic shape change in the tensile bars, suggests very strongly that the damage behaviour is so anisotropic that conventional models are not good enough for a full engineering description of the flat fracture behaviour. Suitable averaging (of shape) in the modelling of the notched bar data, and the companion averaging associated with the 2D model of the C(T) data provide a relatively fast way of transferring engineering data in the tests. There is a discussion of potential ways in which to incorporate 3D effects into the modelling for those purposes where the considerable increase in computational time (due to the microstructurally-sized finite elements needed to capture the damage behaviour) is acceptable in order to include through-thickness effects.
259
Authors: Xiang Hua Kong, Shuai Wang, Yan Hui Sun, Jian Liang Zhang, Xiang Li, Fa Cang Wang, Jian Lin Geng
Abstract: In order to discuss the abnormal fracture in drop weight tear test (DWTT) of API X80 medium-thickness plate, some unqualified samples in DWTT are characterized by SEM, AES, electrolysis and thermal simulation. SEM results show that there are many spherical precipitates in the fracture surface. EDS and AES results show that the abnormal spherical precipitates are carbides including Fe, Ni, Mo, Ti, etc. These precipitates can be extracted by neutral electrolyte method and their EDS results further demonstrate they are carbides. The formationmechanismof the precipitates is discussed based on thermal simulation experiments. When the cooling rate of medium-thickness plate is not enough high, especially in carbide formation area in Fe-C diagram, abnormal spherical carbides will occur and they are harmful for DWTT.
301
Authors: Guang Fu Li, Guo Liang Zhang, Jian Jiang Zhou, Chun Bo Huang, Wu Yang
219
Authors: Jian Huang, Yi Min, Cheng Jun Liu, Mao Fa Jiang
Abstract: To improve the quality controlling of pipeline steel and to avoid mis-down grade, the cleaness including content of non-metallic inclusions, total oxygen and nitrogen of the first continuous casting slags of X70 pipeline steel were investigated. Results showed that, content of total oxygen, nitrogen, large non-metallic inclusions and inclusions areal density decrease with casting length increasing gradually. But at casting length of about 5.0 m which is just during the drastic changeing period of casting speed approaching to stead casting state, the content of large non-metallic inclusions and inclusions areal density increases abruptly induced by the entrapment of mold powders. Thus, to decrease the degradation rate of pipeline slab, the increasing rate of casting speed should be adjusted more evenly.
10
Authors: Nenad Gubeljak, Andrej Likeb, Jožef Predan, Yu. G. Matvienko
Abstract: Thethin walled structures as pipe-line are often unsuitable for standard testingof fracture toughness. One possibility is applying non-standard modifiedspecimens with simple testing procedure, but measured fracture behaviour isconsequence of loading conditions and geometry of specimen. In this paper thedifferences in fracture behaviour of single edge notch bending (SENB) and ringpipe-line bended specimens are discussed. Especially uneven fatigue crack frontas consequence of complex fatigue loading caused different fracture behaviour,than standard single edge notch bending (SENB) specimens. The stress-strainconditions at the crack tip are analysed by finite element modelling. Thecritical crack tip opening displacement has been determined as a crack tipsurface strain-relaxation by using stereo-optical grading method. Comparisonbetween CTOD-R curves of both types of specimens shows difference in crackdriving force.
637
Authors: P. Yan, Özlem Esma Güngör, Philippe Thibaux, Harshad K.D.H. Bhadeshia
Abstract: Large-diameter steel pipes are produced by induction seam-welding followed by induction-assisted heat treatment. The microstructure and distribution of crystal orientations have been studied and related to the mechanical properties of the welded regions. The welding and heat-treatment process leads to a microstructure, a simple observation of which can not explain the observed variations in toughness in the vicinity of the welding joint, because the crystallographic grain size, which represents the scale of similarly oriented adjacent grains, is much coarser than the ordinary grain size. Furthermore, heating the affected zone into the austenite phase field followed by cooling does not completely eliminate the coarse regions of similarly oriented grains. The consequences of this on mechanical properties are discussed.
651
Authors: Hong Mei Yang
Abstract: In order to reduce the production cost, economic-type X70 pipeline steels with the thickness of 14.6 and 15.9mm were redesigned . The latest alloy system of pipeline steel designed by non-molybdenum C-Mn-Cr-Nb alloy system, which replaces the high-molybdenum C-Mn-Mo-Nb alloy system, was adopted along with acicular ferrite microstructure. The microstructure of X70 strip is homogeneous and ferrite grains are fine, resulting in high strength, excellent low-temperature toughness and weldability.
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