Influence of Thermomechanically Controlled Processing on Microstructure and Hydrogen Induced Cracking Susceptibility of API 5L X70 Pipeline Steel
- 1 Downloads
The effect of different thermomechanical controlled processing routes on susceptibility of X70 pipeline steel to hydrogen induced cracking (HIC) have been studied. Two X70 pipeline steel specimens labelled WE and WD were investigated. These specimens have the same chemical composition, but they were processed with seperate thermomechanical treatments parameters. Microstructural examinations showed that WE consists of mainly acicular ferrite and polygonal ferrite, while WD consists of acicular ferrite and bainitic ferrite. After subjecting both specimens to hydrogen charging for 12 and 16 h in 0.2 M sulfuric acid and 3 g/L ammonium thiocyanate, early onset of HIC was observed in specimen WD. Post-hydrogen charging microstructural evaluation showed the nucleation of discontinuous cracks in WD after 12 h of charging. However, extended charging for up to 16 h resulted in HIC along the mid-thickness region of both specimens. Hydrogen diffusion across specimen WE was better than that of specimen WD. Therefore, hydrogen trapping at grain boundaries, banded deformed grains, inclusions and secondary phases such as martensite and cementite aided initiation and propagation of HIC in specimens. Nevertheless, the adverse effect of these features on HIC risks was more prominent in specimen WD compared to specimen WE. The Vickers microhardness values measured in WD (349.6 HV) and WE (307.4 HV) suggest that WD is harder than WE; and higher kernel average misorientation of 0.66° in WD than in WE (0.58°) shows higher dislocation density in WD. The results from slow strain rate tensile test confirmed that specimen WD was stronger and more susceptible to HIC than specimen WE. It was concluded that microstructural phases developed during thermomechanical processing improved strength in WD at the expense of its crack resistance, while WE with lower strength showed more ductility and higher resistance to HIC.
KeywordsAPI X70 Pipeline steel hydrogen induced cracking inclusions microstructure SEM/EBSD/EDS thermomechanical processing
The authors are grateful to Natural Sciences and Engineering Research Council of Canada (NSERC strategic Grant 470033) for their financial support. The test specimens for this study were supplied by Evraz North America, located at Regina, Saskatchewan, Canada. We are specially grateful to canmetMATERIALS Natural Resources, Hamilton, Ontario, Canada for performing the thermomechanical treatments.
- 5.C. Bosch, T. Haase, S. Mannesmann, and F. Gmbh, Effect of NACE TM0284 Test Modifications on the HIC Performance of Large Diameter Pipes, in NACE Corrosion Conference & Expo, 2008, pp. 1–13.Google Scholar
- 9.S. Lynch, Hydrogen Embrittlement Phenomena and Mechanisms, Corros. Rev., 2012, 30(3–4), p 105–123Google Scholar
- 11.S.P. Lynch, Progress towards Understanding Mechanisms of Hydrogen Embrittlement and Stress Corrosion Cracking, in NACE Corrosion, 2007, pp. 1–10.Google Scholar
- 14.V.P. Afanas’ev, T.S. Dolotova, V. V Galtykhina, V.M. Yankovskii, E.A. Solomadina, and E.D. Mokhova, The Influence of Thermomechanical Working Conditions on the Resistance of Low Carbon Steel to Sulfide Cracking, Sov. Mater. Sci. Transl. from Fiz. Mekhanika Mater., 1981, 16(6), p 45–48Google Scholar
- 16.M.A.V. Devanathan and Z. Stachurski, The Adsorption and Diffusion of Electrolytic Hydrogen in Palladium, in Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 1962, p 90–102.Google Scholar
- 18.F. Thebault, S. Frappart, L. Delattre, H. Marchebois, and L.A. Rochelle, Hydrogen Diffusion in Model Molybdenum Containing Steel: A Comparison between Hydrogen Ingress Promoted by H2S or Cathodic Charging, in NACE Corrosion Conference & Expo, 2011, p 1–14.Google Scholar
- 20.D.G. Stalheim and B. Hoh, Guidelines for Production of API Pipelines Steels Suitable for Hydrogen Induced, in Proceedings of the 8th International Pipeline Conference IPC 2010, Calgary, Alberta, Canada, 2010, p 1–11.Google Scholar
- 25.API 5L, “Specification for Line Pipe,” American Petroleum Institute, 2000.Google Scholar
- 29.B. Jeong, R. Gauvin, and S. Yue, EBSD Study of Martensite in a Dual Phase Steel, Met. Mater., 2002, 8, p 700–701Google Scholar
- 42.M.A. Mohtadi-Bonab and M. Eskandari, A Focus on Different Factors Affecting Hydrogen Induced Cracking in Oil and Natural Gas Pipeline Steel, Eng. Fail. Anal., 2016, 2017(79), p 351–360Google Scholar