Role of Nonmetallic Inclusions in Premature Stress-Corrosion Fractures of Drill Pipes

• Published in: Materials science (New York, N.Y.) Vol. 55; no. 6; pp. 822 - 830
• Main Authors: Kryzhanivskyi, E. І., Nykyforchyn, H. М., Student, О. Z., Krechkovska, H. V., Chudyk, І. І.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-05-2020; Springer; Springer Nature B.V
• Subjects: Analysis; Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion; Corrosion fatigue; Corrosion rate; Crack initiation; Crack propagation; Drill pipe; Elongated structure; Fatigue cracks; Fatigue failure; Fracture surfaces; Fractures; High strength steels; Impact tests; Materials Science; Mechanical properties; Nonmetallic inclusions; Oil and gas field equipment; Solid Mechanics; Steel; Stress corrosion; Structural Materials; mechanical characteristics; fractography; drill pipes; corrosion resistance; nonmetallic inclusions
• ISSN: 1068-820X; 1573-885X
• DOI: 10.1007/s11003-020-00375-4

We analyze the causes of the in-service loss of integrity of drill pipes made of G105 steel connected with their premature stress-corrosion fractures. In this case, the mechanical characteristics of steel are satisfactory, except a somewhat lowered elongation. At the same time, both in the structure and on the fracture surfaces of impact test specimens, we reveal a large number of corrosion-active nonmetallic inclusions of the calcium-aluminate type, which may increase the rate of local corrosion by an order of magnitude, promote the formation of deep pits on the inner surface of the pipe, and play the role of sites of initiation of corrosion-fatigue cracks. This is why we assume that the stage of crack initiation, which mainly determines the total durability of drill pipes after premature failures is controlled by the presence of corrosion-active nonmetallic inclusions and their density in the structure of steel.