The mining industry faces a persistent challenge with the premature failure of bolts, particularly due to stress corrosion cracking (SCC). Recent research published in the Journal of Materials Research and Technology sheds light on this critical issue, specifically focusing on the performance of galvanized bolts in the demanding environments of coal mines. The study, led by Zhe He from the School of Mines, State Key Laboratory of Coal Exploration and Intelligent Mining at the China University of Mining and Technology, reveals alarming insights that could reshape bolt usage in underground engineering.
In a groundbreaking examination, He and his team investigated the failure mechanisms of galvanized bolts, which were widely implemented in the Xin’Shang’Hai No. 1 coal mine in China. Despite the initial promise of hot-dip galvanizing as an effective anti-corrosion solution, the bolts experienced extensive failures, prompting a thorough analysis. “Our findings indicate that significant stress concentration occurs on the surface threads of the bolts under high mine pressure, serving as the primary inducer of SCC,” He explained. This discovery is particularly concerning as it highlights the vulnerabilities of galvanized bolts in extreme conditions.
The research demonstrated that under prolonged stress corrosion conditions, the mechanical properties of these bolts deteriorated significantly. The peak strength of galvanized bolts dropped by over 20%, a stark contrast to the more resilient high-strength coated bolts, which largely maintained their original properties. This discrepancy raises critical questions about the reliability of galvanized bolts in high-stress mining environments. He emphasized, “In deep underground engineering, it is not recommended to promote the use of galvanized anti-corrosion processes, especially in environments with high stress and high mineralization.”
Adding to the complexity, the study found a dramatic increase in hydrogen content within the galvanized bolts after service, suggesting a heightened risk of hydrogen-induced cracking (HIC). The presence of HIC-sensitive structures and typical features indicative of HIC further corroborates the risks associated with using galvanized bolts in such environments. He noted, “The instantaneous fracture of galvanized bolts was mainly caused by the interaction of stress concentration cracking due to the geometry of the bolts and HIC under stress corrosion failure.”
These findings are not just academic; they carry significant commercial implications for the mining sector. With the potential for catastrophic failures, mining companies may face increased operational costs and safety hazards. The recommendation to replace galvanized bolts with high-strength coated alternatives could enhance the reliability and safety of bolt support systems, ultimately leading to more efficient mining operations.
As the industry grapples with the realities of material performance under extreme conditions, this research serves as a clarion call for reevaluating bolt specifications in coal mines and potentially other mining operations. The insights provided by He and his team could pave the way for new standards in bolt technology, ensuring safer and more sustainable mining practices.
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