In this study, the effect of specimen geometry on the fatigue crack growth rates (FCGR) in API X65 and X100 pipeline steels was explored using the middle tension and compact tension specimen geometries. It was found that the specimen type has little influence on the stage II linear fatigue crack growth region for these steels. Furthermore, the FCGR behavior in the longitudinal and transverse direction was found to be nearly identical for both steels. Also of interest was a comparison of the FCGR results to the BS 7910 design curves, which showed a discrepancy between the results and the standard only at low ΔK levels. A finite element analysis of the compliance relationships used to predict the crack lengths during testing of both specimen types revealed that the expression for both the middle tension specimen and the compact tension specimen were found to be valid. Although the curved geometry of the middle tension specimen caused slightly different compliance results, these differences did not appear to affect the FCGR results.
Proceedings Title: Proceedings of the 7th International Pipeline Conference
Conference Dates: September 29-October 3, 2008
Conference Location: Calgary, CA
Conference Title: IPC 2008
Pub Type: Conferences
compact tension specimen, CT specimen, fatigue crack growth, middle-crack tension specimen, MT specimen, pipeline steels, X65 steel, X100 steel