Analysis of Bolt Fracture Failure of Floating Head Cover for Heat Exchanger in Medium Pressure Hydrogenation Unit

Abstract Heat exchangers are commonly used in petrochemical production units. Harsh working conditions can lead to catastrophic consequences if failure occurs, making their safe operation crucial for life, health, and productivity. However, the failure of floating head bolts varies under different production processes and operating conditions, making accurate analysis challenging. This paper investigates the fracture of the floating head bolt in a heat exchanger of a medium-pressure hydrogenation unit. The fractured bolt was analyzed using macroscopic observation, chemical composition analysis, mechanical property testing, metallographic inspection, scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The results indicate that the bolt material, a high-strength steel, exhibited high hardness and reduced impact toughness. The fracture originated from corrosion pits on both sides of the stud surface, expanding towards the center and resulting in instantaneous fracture near the center. Based on these findings, the primary cause of the bolt fracture is sulfide stress corrosion cracking in a wet hydrogen sulfide environment. This paper provides improvement suggestions regarding sulfur content control, bolt selection, inspection, and fastening to prevent similar failure accidents.