The resistance of a material against fracture is influenced by its behaviour during the three possible steps of the fracture process, which are crack initiation, crack extension, and crack-arrest. It is the task of materials testing, especially of fracture mechanics, to find out the relevant parameters. To stop a crack in a pipeline in order to limit the crack length it is of great interest to know the crack-arrest toughness, KIa, of the material used.
There are two main possibilities to stop a crack in a pipeline: The first one is to apply special crack arrestors, and the second one is to use a material with a high crack-arrest toughness. The first possibility is rarely realized, and so it is of great interest to gain knowledge of the fracture toughness values of the pipeline steels employed. In the past, big specimens, like Robertson plates for example, were used for the determination of the crack-arrest toughness, KIa, but they are very expensive and so nowadays they are replaced by small specimens like:
1st, the three-point bend specimens (specimens used in a proposal published by TVFA, University of Technology, Vienna),
2nd, the compact-crack-arrest specimens (specimens of the standard test method ASTM E 1221) and
3rd, the full-thickness compact-crack-arrest specimens (specimens proposed in the test method of Ripling and Crosley).
This work deals with the determination of the crack-arrest toughness, KIa, of the base material, the weld metal and the heat affected zone of a weld of the pipeline steel X 70. For this purpose tests were performed with each of the three materials, employing each of the three mentioned test specimens. Finally, this work contains a discussion and a comparison of the measured crack-arrest toughness values.
