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  Title Characterizing the fracture resistance of ERW seams
  Author(s) Dr Brian Leis  
  Abstract RECENT WORK HAS SOUGHT to quantify the fracture resistance of ERW seams using Charpy-vee notch (CVN) impact specimens removed transverse to the pipe axis that were selectively notched to interrogate the bondline, aspects within the upset region, or the base metal remote to the seam. In spite of precisely locating the notch, and evaluating mutually adjacent sites along the seam, such results can be widely scattered. Related work suggests that the total energy measured in such tests represents the composite dissipation as the crack initiates and progresses into the bondline and/or into the upset, seeking the path of least resistance regardless of where the notch was initially placed. As shifts in the crack path can occur in-service, as well as in pressure testing or laboratory testing, such response opens to potential issues when evaluating seam performance relative to the results of inline inspection. Likewise, it opens to uncertainty in establishing “representative” properties for use in fit-for-service integrity assessments. This paper first reviews the macro and microstructural traits of modern high- frequency seams in contrast to those for the low-frequency process. The nature of the microstructure formed across the narrower HF seam is contrasted to that evident for the broader LF seam, and the potential effects of the gradient evident therein are discussed. It is shown that this gradient is associated with inherently different resistances as the crack path tracks the bondline in contrast to weaker planes in the upset seam. Detailed metallography is coupled with enhanced optical fractography to illustrate properties variability due to the differing CVN energies associated with these crack paths. It is shown that quantitatively accurate fit-for-service predictions can be made for defect response to pressure by comparison of model results with those for case-specific burst tests. The implications for integrity management are discussed, which point to occasionally misguided fit-for- purpose results depending on the “representative” cracking resistance that is adopted for that purpose.  
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