Effect of Orientation on CVN and K-CVN Toughness Correlation of SAW Pipe Seam Welds

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Abstract Charpy absorbed energy (CVN), and fracture toughness (stress intensity factor K) using single-edge notched bend (SE(B)) specimens, were measured for submerged-arc welded (SAW) pipe seam welds using two typical two-pass seam welds. Because the intent is to derive K values for engineering critical assessment (ECA) of surface flaws, a correlation between K and CVN was assessed. A crack depth of a = 2 mm was used (i.e. the normal notch depth for CVN specimens, and similar target depth for SE(B) specimens representative of real-world weld flaws). The effect of orientation on CVN values was studied because a through-thickness notch (TTN) is specified in standards but a surface notch (SN) is more relevant for real-world flaws. The results indicate that there is little effect of orientation on CVN of TTN and SN specimens for these X70 and X100 SAW seam welds, implying that TTN specimens can be used to infer SN specimen values. To be relevant to Charpy tests in lower-transition or lower-shelf regions, fracture toughness tests were performed at the corresponding temperatures. Most SE(B) specimens showed some ductile tearing before instability except for the specimens of X100 weld at −45°C that displayed full ductile tearing. Ductile fracture initiation toughness values (J0.2) were stable over the temperature range studied. Fracture toughness (Ju) corresponding to instability (cleavage fracture) increased with temperature along with CVN values that ranged from 24 J to 69 J for X70 and 45 J to 95 J for X100. Based on results of these two SAW welds, the BS 7910 K-CVN correlation was found to yield highly conservative estimates of K for a shallow-notched external surface flaw from CVN.

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