axially running cracks. In the past decades, discussions and research have been in that the TCM approach, among with others, could not accurately predict either fracture speed or minimum arrest fracture toughness for high-grade pipes, and with pipe grade increasing the prediction errors are getting larger. Recent research work at TransCanada indicates that for a better prediction of pipeline ductile fracture, understanding the basic material mechanical behavior and its fundamental fracture mechanism is essential. One of the important findings of the work is that pipe material fracture toughness is not a constant as being commonly treated, rather the fracture toughness, in terms of both steady-state CTOA and steady-state DWTT fracture energy is fracture speed dependent, being decreasing with increasing fracture speed. Corresponding modifications have been made to the traditional TCM by introducing speed-dependent fracture toughness. The improved model gives much better predictions in both fracture speed and toughness for high grade pipes. This paper presents recent work at TransCanada, together with its industry partner Engineering Mechanics Corporation of Columbus (EMCC), on high-speed pipe-material fracture testing technique (using the modified back-slot DWTT specimen) and high-grade material testing data. The test data supports the predictions of early published work on speed-dependent fracture toughness. The fracture speeds obtained from the modified back-slot DWTT specimens were very close to actual full-scale pipeline ductile fracture speeds and this in turn enhanced the applicability of the modified TCM model.
IPC2010-31022
EVALUATION OF DOUBLE JOINTING GIRTH WELDS OF HIGH GRADE LINE PIPES 高钢级管线管双面环焊缝的评价 Da-Ming Duan, Robert Lazor and David Taylor TransCanada PipeLines Limited
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450- 1 Street, S.W. Calgary, AB, T2P 5H1 Canada
ABSTRACT Double jointing is an effective approach for pipeline construction in terms of both welding productivity and consistent weld quality as a result of a controlled working environment. However, the high heat input associated with the submerged arc welding (SAW) process used for double jointing must be considered with respect to the material properties of both heat affected zone (HAZ) and the weld metal of double jointing welds. This is particularly important for strain-based design pipeline applications utilizing high grade pipe, such as X80 and X100. High grade pipe materials achieve their strength as a result of controlled rolling practices that produce a fine grained steel. High heat input welding results in an increased grain size in the heat-affected zone, and often results in

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