PSI - Issue 2_A

Toshihiko Amano et al. / Procedia Structural Integrity 2 (2016) 422–429 "Toshihiko Amano et. al." / Structural Integrity Procedia 00 (2016) 000–000

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Fig. 10 comparers the plastic strain in the traverse direction near the crack front for the SPC-DWTT tested at -10 o C in between the specimen with AFA and without AFA. Approximately 4.0 % of the compressive pre-straining occurred after the static bending test in the specimen appeared AFA in DWTT while 2.0 % of the compressive pre straining occurred in the specimen without AFA in DWTT. Fig. 10 (b) shows the plastic strain after the SPC-DWTT. Fig. 10 (b) also shows the plastic strain measured in the partial gas burst test using the scribed grid. The plastic strains in the SPC-DWTT specimen without AFA were lower than that in pipe. On the other hand, for the SPC DWTT specimen with AFA, the plastic strains at both the hammer impact side and the root of notch side which appeared the brittle fracture were larger than that measured at the fully ductile fracture region. Therefore, the abnormal fracture occurs easily because the range of strain in hammer impact side was relatively high. 4. Conclusions In this study, the DWTTs with the pressed notch (PN), the chevron notch (CN), the pre-cracked notch (SPC) and the partial gas burst test were conducted in order to compare the brittle-to-ductile transition temperature. The effect of pre-straining near the impact hammer side in the SPC-DWTT specimen was also evaluated at static three-point bending test. Charpy impact specimens were taken from quasi-static loaded and unloaded DWTT specimen to measure the possible influence of pre-straining on toughness. Based on these experiments, the relationship between the pre-straining and the abnormal fracture appearance was considered. The main conclusions obtained in this study are as follows;  The brittle-to-ductile transition curves in the CN-DWTT and the SPC-DWTT shifted toward a higher temperature side compare to that in the PN- DWTT. However, the abnormal fracture appeared regardless of types of notch in the transition region.  The fracture appearances in the pipe burst test were similar to that in the SPC-DWTT specimen which is easy to initiate the brittle fracture due to reducing crack initiation energy while the abnormal fracture occurred at near hammer impact side.  More than 2 % of compressive and tensile pre-straining gave 7 to 10 % decreases of the Charpy upper-shelf energy. Further investigation such as brittle-to-ductile transition curve of Charpy test obtained from pre strained materials is needed to relate abnormal fracture occurrence to embrittlement behavior caused by pre straining.  The abnormal fracture appearance located at above the 85 % SATT occurred due to the pre-strain effect and the deflection due to bending prior to crack initiation. Acknowledgements The authors would like to thank Nippon Steel & Sumitomo Metal Corporation for support in preparing this reports and permission to publish the results. The authors also wish to acknowledge Nippon Steel & Sumikin Technology Co. in the execution of the DWTT and the partial gas burst test. References American Petroleum Institute (API), 1996. API Recommended Practice for Conducting Drop-Weight Tear Tests on Line Pipe. API RP 5L3. Fujishiro, T., Hara T. and Aihara, S., 2012. Effect of plastic deformation on occurrence of abnormal fracture during DWTT, 9th International Pipeline Conference (IPC2012) , Calgary, Canada, Paper #IPC2012-90165. Hasenhütl, A., Erdelen-Peppler, M., Kalwa, C., 2014. Inverse fracture – What is it all about?, 10th International Pipeline Conference (IPC2014) , Alberta, Canada, Paper #IPC2014-33476. Hwang, B., Lee, S., Kim, Y.M., Kimi, N.J., Yoo J.Y. and Woo, C.S., 2004. Analysis of abnormal fracture occurring during drop-weight tear test of high-toughness line-pipe steel. Materials Science and Engineering, A368, 18-27. Kiefner, J. F., Maxey, W. A., Eiber, R. J., and Duffy, A. R., 1973. Failure Stress Levels of Flaws in Pressurized Cylinders. ASTM STP 536, 461 481. Sakimoto, T., Igi, S., Oi, K., Aihara, S., 2013. The pre-straining effect on inverse fracture in DWTT for high toughness linepipe, 6th International Pipeline Technology Conference, Ostend, Belgium, Paper# S20-02. Wilkowski, G., Shim, D-J., Hioe, Y., Kalyanam, S., and Brust, F., 2012. How new vintage line-pipe steel fracture properties differ from old vintage line-pipe steels, 9th International Pipeline Conference (IPC2012) , Calgary, Canada, Paper #IPC2012-90165.