All-Russian Scientific and Research Institute of Tube Industry — RosNITI (Chelyabinsk, Russia):

Pyshmintsev I. Yu., Dr. Eng., General director, e-mail: PyshmintsevIU@tmk-group.com
Struin A. O., Cand. Eng., Deputy Head of Department on Direction «Welded Tubes», e-mail: struin@rosniti.ru
Kvashnin V. D., Junior Researcher, e-mail: Kvashnin@rosniti.ru

Gent University (Gent, Belgium):
Gervasyev A. V., Cand. Eng., Researcher, Department of Metal Science, e-mail: GervasyevAM@sinara-group.com
Petrov R. Kh., Dr. Eng., Prof., Department of Metal Science, e-mail: Roumen.Petrov@UGent.be

It is shown that anisotropy of strength and toughness properties is observed in the investigated ferrite-bainite steels. Maximal, average and minimal strength values are noted in T-direction, Z-direction and L-direction respectively. Three kinds of anisotropy behaviour (“saw-toothed” “serrated”, yield tooth and continuous strengthening) can be seen on deformation diagrams for small deformation degree values. It is concluded that the kind of deformation diagram does not vary and strength increases with lowering of testing temperature. Toughness anisotropy is displayed more distinctly than strength anisotropy. Impact toughness in Z-direction is significantly lower than in T- and L-directions. Brittle component in fracture of drop-weight testing samples in Z-direction is observed at room testing temperature. The conducted tests allowed to determine power capacity of splitting forming. Impact toughness in Z-direction makes less than 30 J/cm² at the temperature –20 °C and for notch location on ½ of sample thickness. The tests for determination of static cracking resistance have shown that splitting can occur at the load about 30 % of the load required for start of cracking propagation in T-direction. The analysis of microstructure conducted both previously and in this work allow to conclude that splitting susceptibility in K65 steels is determined by combination of several parameters, and presence of stretched areas with {001}<110> orientation as well as high content of large particles of “secondary” phases can be considered as the main among these parameters.

1. Stalheim D. G., Barnes K. R., McCutcheon D. B. Alloy Designs for High Strength Oil and Gas Transmission Linepipe Steels. International Symposium on Microalloyed Steels for the Oil and Gas Industry. 2007.
2. Nobuhisa S., Igi S., Masamura K. Seismic Integrity of High-Strength Pipelines. JFE Technical Report. 2008. No. 12. October.
3. Suzuki N., Arakawa T., Arabey A. Strain-Based Pipeline Design in Harsh Environments Using Large Diameter High Strain Line Pipes. Proceedings of the 2014 IPC, September 29 – October 3, 2014, Calgary, Alberta, Canada.
4. Gray J. M. Ductile Fracture of Gas Pipelines: Correlation Between Fracture Velocity and Plastic Zone Defi ned From Tension Test Parameters, Final Report AGA Project # NG-18(4), Report No. MA/AGA/84/1, February 1984.
5. Pyshmintsev I. Yu., Arabey A. B., Esiev T. S. et al. Energoemkost razrusheniya trubnykh staley klassa prochnosti K65 (Kh80) (Energy Intensity of K65 (X80) Grade Pipe Steel Fracture). Nauka i tekhnika v gazovoy promyshlennosti = Science and Technology in the Gas Industry. 2011. No. 4. pp. 63–72.
6. Leis Br. N. Alternative view of fracture propagation in pipelines. Proceedings of 6th International Pipeline Technology Conference, Ostend, Belgium, 6–9 October, 2013.
7. Rusakova V. V., Lobanova T. P. Perspektivy primeneniya vysokoprochnykh trub kategorii prochnosti K65 (Kh80) i vyshe dlya proektov dalnego transporta gaza (Prospects for Application of High-Strength К65 (Х80) Linepipes for Long-Distance Gas Transmission Projects). Nauka i tekhnika v gazovoy promyshlennosti = Science and Technology in the Gas Industry. 2009. No. 1. pp. 4–8.
8. Le Pera F. S. Improved Etching Technique for the Determination of Percent Martensite in High-Strength Dual-Phase Steels. Metallography 12:263–268. 1979. pp. 263–268.
9. Rules for classification of ships. Мaterials and welding. Рart 2 Сhapter 1. General requirements for materials.
10. R. W. K. Honeycombe. Plasticheskaya deformatsiya metallov (Plastic Deformation of Metals). Moscow : Mir, 1972.
11. Pyshmintsev I., Gervasyev A., Petrov R. H. et al. Crystallographic Texture as a Factor Enabling Ductile Fracture Arrest in High Strength Pipeline Steel. Materials Science Forum. 2012. Vol. 702–703. pp. 770–773
12. Gervasyev A., Carretero Olalla V., Pyshmintsev I. et al. X80 Pipeline Steel Characteristics Defining the Resistance to Ductile Fracture Propagation. Proceedings of the 6th Interantional Pipeline Technology Conference, Ostend, Belgium, 6–9 October 2013. pp. S19–02.