Critical subsea connector bolts have been failing for over a decade, with the underlying causes still not fully understood. This study investigates the influence of preload torque, subsea water currents, and corrosion protection on the failure of ASTM A193 Grade B7 bolts using laboratory experiments and finite element analysis. Results indicate that each factor significantly accelerates corrosion, and their combined effect produces a dramatic increase in corrosion rate, providing new insights into the mechanisms behind these persistent failures.
Location
Online
Date
1 December 2020
Time
5:00 PM
Bio / Abstract
The unexpected failure of critical subsea connector bolts remains a major concern for the industry, despite the replacement of over 10,000 bolts and multiple investigations and quality control recommendations. The root causes of these failures have not been fully identified.
This study focuses on the impact of three parameters on the failure mechanism of ASTM A193 Grade B7 (AISI 4140) steel bolts: varying preload torque, intensities of subsea water currents, and the effectiveness of standard corrosion protection methods, such as galvanization.
The experimental setup consists of a flange with eight 5/8-inch diameter bolts, each 3/4-inch long, fastened with sixteen nuts. Bolt-nut units were subjected to different torque levels and immersed in a 3.5% NaCl aqueous solution for three weeks. Finite element method (FEM) analysis was conducted to predict vulnerable areas, while corrosion tests and visual/SEM inspections provided detailed insights into failure mechanisms.
Key findings include:
- The corrosion rate at vulnerable bolt locations is 34% higher than at the edges.
- High subsea water currents increase corrosion by 39%.
- Elevated torque accelerates corrosion by 45%.
- The combination of all three factors produces a 279% surge in corrosion rate.
These results reveal how mechanical and environmental conditions interact to produce catastrophic bolt failures and offer a pathway for mitigating such risks in subsea infrastructure.
Biography
Mr. Ofer Medlinsky is a PhD student in Oil, Gas & Energy Engineering at the University of Nicosia. He holds a BSc and MSc in Materials Engineering from Ben-Gurion University, Israel, and an MBA from Heriot-Watt University, Israel.
He has industry experience as Lubricants Department Manager at Chevron Israel (2007–2011) and Group Leader at Intel (Fab28) (2012–2016). Since 2017, he has been an Adjunct Lecturer at the Mechanical Engineering Department, Sami Shamoon College of Engineering.
His research focuses on materials science and metallic corrosion. Outside of academia, Ofer enjoys camping with family and friends and is an avid table tennis player.