Session: 03-01-01 Fracture Assessment and Control

Paper Number: 78918

78918 - Transitions in Charpy Energy and Splitting for X70 and X80 Pipe Steel 

Using data obtained for a standard production 42-inch X70 pipe 19.6 mm wall thickness from about 2006 and a 24-inch diameter X80 pipe 0.5 mm wall thickness from about 2016, the transition in fracture behavior between fully brittle and fully ductile 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 both increase and 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 for the tested material with 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 compared to brittle fracture alone by releasing constraint on crack initiation behavior at the machined notch and occurs at temperatures just above the lower shelf temperature, where brittle fracture dominates, including below -100°C. Splitting across the notch tip decreases Charpy energy compared to splitting across the ligament only. The splitting behavior can also be correlated to effects on fracture toughness in the same orientation for CTOD specimens in the base material, both for toughness determined at a pop-in event and for toughness determined at maximum load.

Presenting Author: William Mohr EWI

Authors:

William Mohr EWI
Tom Mcgaughy EWI