Tiksomet Ltd., St. Petersburg, Russia:
A. A. Kazakov, Dr. Eng., Professor, Head of the Laboratory for Metallurgical Expertise, e-mail: kazakov@thixomet.ru

JSC Vyksa Metallurgical Plant, Vyksa, Russia:
V. A. Murysev, Chief Specialist of the Engineering and Technology Center
I. V. Rybalchenko, Head of the Laboratory of Metal Science and Heat Treatment of metals (MiTOM), Central Plant Laboratory
P. P. Stepanov, Cand. Eng., Director of the Engineering and Technology Center

Abstract: An incisive analysis of studies of the most frequent defects of pipe joints obtained by high-frequency electric resistance welding (HFW) is included herein with particular focus on nonmetallic inclusions (NMIs), which are the cause of defects in such welded joints. Their composition, origin and methods of elimination under industrial conditions are discussed. In order to validate the nature of defects the interpretation procedure of the composition of NMIs detected in the discontinuities of welded joints has been developed. Examples of its application on the low-carbon line pipe steels of different grades X52–X56 are presented. The compositions of NMIs found in 64 defects of welded joints of A 516-55 (09G2S) steel pipes are summarized. These compositions significantly differ from each other and correspond to the different nature of NMIs: indigenous deoxidation products based on spinel MgO∙Al₂O₃ (8 %), products of steel modification by calcium (62 %), exo-indigenous NMIs with residuals of mould flux (4 %) or MgO (8 %) and indi-exogenous NMIs based on MgO (18 %). The unique variation ranges of the main elements included in these groups of NMIs are used for automated determination of their origin when carrying out metallographic examination of defects by means of the Thixomet image analyzer in the conditions of factory practice. The detailed origin of NMIs makes it possible to indicate the exact location in the technology of ladle treatment and steel casting for their improvement and to enhance on this basis the quality of line pipe joints obtained by HFW.

1. Technician ERW Weld Discontinuity Characterization Guide. For the API Long Seam Pipeline (LSP) exam. Available at: https://www.api.org/-/media/Files/Certification/ICP/ICPCertification-Programs/UT%20Programs/LSP/Technician%20Characterization%20Guide%20for%20API%20LSP%20Exam.pdf?la=en&hash=6A3CA97BDDCE851B0CBBAC81ACCD55311BFC7E21 (accessed: 07.06.2022).
2. API Bulletin on Imperfection Technology, API Bul. 5T1 (R2017), 2017. 65 p. Available at: https://standards.globalspec.com/std/10185662/api-bull-5t1 (accessed: 07.06.2022).
3. Fazzini P. G., Cisilino A. P., Otegui J. L. Experimental validation of the influence of lamination defects in electrical resistance seam welded pipelines. International Journal of Pressure Vessels and Piping. 2005. Vol. 82. pp. 896–904.
4. Joo M. S., Noh K. M., Kim W. K. et al. A Study of Metallurgical Factors for Defect Formation in Electric Resistance Welded API Steel Pipes. Metallurgical and Materials Transactions. 2015. Vol. 2, Iss. 2. pp. 119–130. DOI: 10.1007/s40553-015-0049-6.
5. Tiratsoo J. Managing pipeline threats. Editor QR 11-9. Hook cracking. Available at: https://pipeline-threats.com/plthreats/qr-11-9-hook-cracking (accessed: 07.06.2022).
6. Sima A. Y., Hossein E., Mehrdad F. Hook crack in electric resistance welding line pipe steel. Australian Institute for Innovative Materials – Papers. 2003. 1409. Available: https://ro.uow.edu.au/aiimpapers/1409
7. Ghosh A. Secordary Steelmaking – principles and applications. CRC Press, 2000. 344 p.
8. Kyada T., Raghu Shant J., Goyal D. et al. Analysis of Micro Cracks Near Weld Line in ERW Pipe of API 5L X70M Grade. Journal of Failure Analysys and Prevention. 2015. Vol. 15. pp. 344–350. DOI: 10.1007/s11668-015-9950-7.
9. Shin M. H., Han J. M., Lee Y. S., Kang H. W. Study on Defect Formation Mechanisms in ERW for API Steel. Proceedings of Biennial International Pipeline Conference IPC. 2014. Vol. 3. p. 5.
10. Eaves G. N., Cameron S. R., Casey V. J., Nestico P., Bernert W. Hook Crack reduction in ERW line pipe steel. Steelmaking Conference Proceedings. 1992. pp. 521–528.
11. Tsai H. Thomas. Characterization of Hook Cracks in Tubular Products and Countermeasures 2007. Proceedings of the International Conference “China Iron and Steel”. 2007.
12. Sofras Ch., Bouzouni M., Voudouris N., Papaefthymiou S. Investigation of penetrator defect formation during high frequency induction welding in pipeline steels. MATEC Web of Conferences ICEAF-VI. 2021. Vol. 349.
13. Okabe T., Toyoda S., Goto S., Kato Y., Yasuda K., Nakata K. Numerical Analysis of Welding Phenomena in High-Frequency Electric Resistance Welding. KEM. 2014. Vol. 622–623. pp. 525–531.
14. Kaba M., Altay M., Çimenoğlu H. An Investigation on the Longitudinal Cracking of Electric Resistance Welded Steel Pipes. Journal of Failure Analysys and Prevention. 2020. Vol. 20. pp. 657–662.
15. Kim C. M., Kim J. K. The effect of heat input on the defect phases in high frequency electric resistance welding. Metals and Materials International. 2009. Vol. 15. pp. 141–148.
16. Adaba O. et al. An SEM/EDS Statistical Study of the Effect of Mini-Mill Practices on the Inclusion Population in Liquid Steel. Proceedings of the 9^th International Conference and Exhibition on Clean Steel. 2015, Budapest. Hungary Volume, Chapter 4, Paper 5.
17. Kazakov А. А., Murysev V. А., Kiselev D. V. Interpretation of nature of non-metallic inclusions in assessing the quality of metal products in the industrial conditions. Chernye Metally. 2021. No. 9. pp. 47–54.
18. GOST 31447–2012. Steel welded pipes for trunk gas pipelines, oil pipelines and oil products pipelines. Introduced: 01.01.2015.
19. GOST 59496–2021. Steel welded pipes. Defects of welded joints. Terms and definitions. Introduced: 01.06.2021.
20. Kazakov A. A., Murysev V. A., Kiselev D. V. Non-metallic inclusions interpretation technique for factory expertise of metal product defects. CIS Iron and Steel Review. 2021. Vol. 22. pp. 41–49.
21. Li Y., Yang W., Zhang L. Formation mechanism of MgO containing inclusions in the molten steel refined in MgO refractory crucibles. Metals. 2020. Vol. 10. 444 p.
22. Liu Ch., Gao Xu, Kim S.-j., Ueda Sh., Kitamura Sh. Dissolution behavior of Mg from MgO–C refractory in Al-killed molten steel. ISIJ International. 2018. Vol. 58, Iss. 3. pp. 488–495.