Elastic interaction in bolted flange joints during hot bolting and disassembly

Abstract

Bolted flange joints are critical structural components used in a wide range of industrial applications, including petrochemical facilities, oil and gas pipelines, and power plants. Despite their apparent simplicity, the mechanical behavior of these joints under complex loading and service conditions remains a key concern in both design and post-construction maintenance. One particularly sensitive procedure while the system remains under operating pressure is the removal or replacement of bolts commonly known as hot bolting. Although often treated as a routine operation, improper handling during bolt untightening can lead to catastrophic outcomes, including loss of gasket compression, flange separation, bolt overstressing, or even system failure. This thesis presents a comprehensive investigation into the elastic interaction of bolted flange joints during the untightening process. Emphasis is placed on understanding how the removal of individual bolts influences the stress redistribution in the remaining bolts, the deformation of the gasket, and the contact pressure exerted on the gasket. A finite element modeling (FEM) approach is adopted to simulate the mechanical response of ASME B16.5 Class 900 welding neck flanges equipped with spiral wound gaskets, under bolt preload conditions. The FEM simulations, conducted using ANSYS, examine key parameters such as bolt stress evolution, vertical displacement, and gasket contact stress during different bolt removal sequences. The experimental results are validated against analytical and FEM models to ensure the reliability of the numerical and analytical predictions and compared with experimental results. By characterizing the interaction behavior during bolt unloading, this study provides critical insights into the thresholds beyond which joint integrity and leak tightness may be compromised. Furthermore, it explores the conditions under which controlled hot bolting procedures can be safely executed without requiring additional clamping tools provided that elastic stress redistributions are well-understood and managed within acceptable safety margins. The findings of this work contribute to enhanced design recommendations, improved safety protocols, and more efficient maintenance strategies for bolted flange assemblies in high-risk operational settings.

Date	16 Nov 2025
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Hakim A. Bouzid (Supervisor)