Abstract
Using data obtained for a standard production 42-inch X80 pipe with a 19.6-mm wall thickness produced around 2006 and a 24-inch diameter X70 pipe having a 0.5-inch (12.5-mm) wall thickness produced in 2016, the transition between fully brittle and fully ductile fracture behavior has been examined to assess any effects of transverse splits or delaminations. This is compared with a 48-inch X80 pipe from recent production. The 24-inch diameter pipe split more than the others, but all three showed splitting in the transition. The additional surface area formed at the splits can increase or decrease the Charpy energy by expending energy to form more fracture surface but also reducing constraint on the propagating crack as it extends through the unnotched Charpy ligament. Fitting of full Charpy energy transition curves using standard hyperbolic tangent functions does not represent the behavior well. An important transition is noted in the behavior between splitting that initiates at the initial notch tip and splitting that occurs further down in the ligament. Spitting across the notch tip increases Charpy energy by releasing constraint on crack initiation at the machined notch and occurs at temperatures just above the lower shelf temperature, where brittle fracture dominates. Splitting across the notch tip also decreases Charpy energy as compared to splitting across the ligament only. The Charpy splitting behavior also correlates to similar effects in crack tip opening displacement (CTOD) specimens for the same specimen orientation in the base material, both for conditions where unstable fracture and fully ductile response occurs.
