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2024 №04 (03) DOI of Article
10.37434/tdnk2024.04.04
2024 №04 (05)

Technical Diagnostics and Non-Destructive Testing 2024 #04
"Tekhnichna Diahnostyka ta Neruinivnyi Kontrol" (Technical Diagnostics and Non-Destructive Testing) #4, 2024, pp. 23-31

Study of intercrystalline corrosion cracking in welded joints of Chornobyl NPP pipelines. Materials science aspect

V.M. Torop, M.D. Rabkina, E.O. Davydov

E.O. Paton Electric Welding Institute of the NAS of Ukraine 11 Kazymyr Malevych Str., 03150, Kyiv, Ukraine. E-mail: v.torop@gmail.com

Stress corrosion cracking, similar to intergranular corrosion in austenitic steel welds, primarily affects grain boundaries in the heat-affected zone when exposed to a corrosive environment, leading to sensitization – a reduction in structural integrity, which causes cracking and grain loss. The object of research were samples cut out of «coils» of pipelines of the 3rd power unit of the Chernobyl NPP in the areas of damaged welded joints. Based on radiographic and ultrasonic inspection of pipeline welds, as well as determination in the examined samples of the content of alloying elements, mechanical properties, metallographic, fractographic and micro-X-ray spectral studies, including investigation of fracture surfaces of samples that were cyclically loaded, taking into account fatigue grooves, and with regard to solution of the problem of corrosion cracking of austenitic steels in boiling water reactors, a set of measures was developed: long-term measures – replacement of steels with others not prone to corrosion cracking; short-term measures – application of external weld coating, repair of defective areas, relieving residual stresses; temporary measures – justification of the admissibility of the defective weld for operation. 9 Ref., 5 Tabl., 8 Fig.
Keywords: radiographic and ultrasonic inspection of welded joints, intergranular corrosion, stress corrosion cracking, corrosion-resistant steel, pipelines, alloying elements, chromium carbides, fatigue grooves

Received: 17.10.2024
Received in revised form:27.11.2024
Accepted: 20.12.2024

References

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7. (1988) Instruction on investigation of state of metal of NPP pipelines using cut-out samples after 100 thou h of operation (AI-35- 17-86). Moscow, VNIIAES. Introd. 30.04.88 [in Russian]. 8. GOST 6032-89: Corrosion-resistant steels and alloys. Moscow, Izd-vo Standartov, 1990 [in Russian].
9. (2002) IAEA-EBP-IGSCC Mitigation of intergranular stress corrosion cracking in RBMK reactors. Final Report of the Programme's Steering Committee. IAEA-EBP-IGSCC. A publication of the extrabudgetary programme on mitigation.

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