PSI - Issue 42

Available online at www.sciencedirect.com Available online at www.sciencedirect.com ^ĐŝĞŶĐĞ ŝƌĞĐƚ Structural Integrity Procedia 00 (2022) 000 – 000

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Procedia Structural Integrity 42 (2022) 1406–1413

23 European Conference on Fracture - ECF23 Pecularities of fatigue cracks growth in steel and composite sucker rods Halyna Krechkovska a,b, *, Bogdan Kopey c , Bohdan Bakun c , Ihor Kopey c

a Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova St., Lviv, 79060, Ukraine b Lviv Polytechnic National University, 12, Stepana Bandery St., Lviv, 79000, Ukraine c Ivano-Frankivsk National Technical University of Oil and Gas,15, Karpatska str., Ivano-Frankivsk, 76019, Ukraine

Abstract

To predict the fatigue life of sucker rods, it is important to take into account the effect of technological environments under various loading schemes on the conditional fatigue limit of steels used for their manufacture (in particular, such as steel 20N2M), and compare these properties with modern materials for the manufacture of fiberglass and hybrid sucker rods (with metal heads and polymer rod) as prototypes of steel elements of oil-producing equipment. Specimens of sucker rods with technological or operational defects were tested for fatigue life-time in aggressive technological environments. It has been established that the fatigue life-time and fatigue endurance of sucker rods decrease with an increase in their diameter. So, with a test base of 10 7 loading cycles, the endurance limits of rods with a diameter of 19, 22, and 25 mm were 95, 85, and 80 MPa, respectively. It was shown that technological defects practically did not affect the life-time of the rods. Minor differences were associated with the scatter of the fatigue characteristics of the metal. Defects formed in rods during their operation in wells have a more noticeable effect on their life-time under variable loads. It was found that the resource of sucker rods with a diameter of 19 mm decreased faster compared to rods with a diameter of 22 mm in the presence of operational defects of the same depth in both rods. This is due to the greater sensitivity of smaller diameter rods to defects. According to the curves of the crack growth rate in specimens made of sucker rods with a diameter of 22 mm, it was found that the critical state (according to the jump in the crack growth rate) is reached if the crack length along the perimeter of the rods is within 15...16 mm, and its depth is 4.5 ... 5.6 mm. Such cracks were fixed at a stress range of 100 MPa, which is commensurate with the operating loads of the rods. For rods of other standard sizes, the critical crack depth, which preceded the almost spontaneous destruction of the specimens, was 3...4, 4...5 and 5...6 mm for rods with a diameter of 16, 19 and 25 mm, respectively. In article we also evaluated fatigue life on samples of fiberglass sucker rods under cyclic loading by circular cantilever bending and obtained the corresponding fatigue curves. According to the results of these tests, probabilistic curves of 10 7 of the rods. Minor differences were associated with the scatter of the fatigue characteristics of the metal. Defects formed in rods

* Corresponding author. Tel.: +380-67-81-12-543; E-mail address: krechkovskahalyna@gmail.com

2452-3216 © 2022 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the conference Guest Editors

2452-3216 © 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 23 European Conference on Fracture – ECF23 10.1016/j.prostr.2022.12.179