Fracture Failure of Dropper Wires in the Power Supply System of a Subway Line
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CASE HISTORY—PEER-REVIEWED
Fracture Failure of Dropper Wires in the Power Supply System of a Subway Line Guoqiang Liu . Ning Ding . Jing Zhou . Na Xu . Weimin Guo
Submitted: 18 February 2020 / in revised form: 6 October 2020 / Accepted: 1 November 2020 Ó ASM International 2020
Abstract Batch of dropper wires in the power supply system of a subway line fractured in the past several years. The dropper wires are made of soft stainless steel wire (Grade 304) with a diameter of 3.0 mm. The subway line in which the dropper wires often fractured is built near the sea. In this work, failure mechanism of the fractured dropper wires was explored based on the macro- and micro-examinations. Several technologies including scanning electron microscopy and energy-dispersive x-ray spectroscopy were utilized to reveal the mechanism. The failure mechanism of the dropper wires is considered as fatigue fracture. Its chemical composition and mechanical properties meet the standard of 304 stainless steel. The microstructure of the failed dropper wires is normal. Influence of the corrosive environment promotes the initiation of the fatigue cracks. Keywords Dropper wire Fatigue Fracture Pitting corrosion Stainless steel
G. Liu J. Zhou Qilu University of Technology (Shandong Academy of Sciences), Shandong Machinery Design & Research Institute, Jinan 250031, People’s Republic of China N. Ding (&) N. Xu W. Guo Qilu University of Technology (Shandong Academy of Sciences), Shandong Analysis and Test Center, Engineering Research Center of Failure Analysis and Safety Assessment, Jinan 250014, People’s Republic of China e-mail: [email protected]
Introduction In many industries such as chemical, petroleum and even some infrastructure, mechanical equipment usually works in a severe working condition. There are many challenges for the materials and components, for instance, intense heat, humidity, corrosive medium and so on. Environmental factor becomes one of the most important external causes which might lead to serious failure of engineering components [1–3]. Among all of the environmental factors, the destructive effect of corrosive environments on metal components cannot be ignored [4–6]. Appearance of the corrosive environment will lead to uniform or localized corrosion damage on the surface of components in service, reducing their performance and increasing the risk of failure. As the rate of localized corrosion is often orders of magnitude greater than that of uniform corrosion, more attention should be paid to the damage caused by localized corrosion, such as pitting corrosion, intergranular corrosion, stress corrosion cracking and so on. Sometimes, localized corrosion will induce other failure modes. For instance, due to the stress concentration induced by corrosion pits, initial fatigue cracks may easy to generate at the bottom of the pit [7, 8]. Under a cyclic load, the initial crack may propagate and lead to fracture of the component. Dropper wire is a type of foundational parts of the catenary in the power sup
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