Session: CT-04-01 Assembly of Bolted Joints-1

Paper Number: 154415

154415 - Elastic interaction of bolted flange joints during untightening 

Abstract: 

Replacing corroded or damaged bolts in bolted flange joints is an inevitable maintenance procedure for pipelines and equipment, especially for pipelines in high-pressure and high-temperature condition. Performing this task without suspending operations is critical to ensure minimal disruption and maintain the continuity of services. This procedure, commonly referred to as hot bolting, is described in the PCC-1 Guidelines for Pressure Boundary Bolted Flange Joint Assembly and ASME PCC-2 standards. Despite the guidelines, the industry tends to use specialized tools and apply high safety margins, primarily because of the uncertainties associated with the behavior of bolts under such extreme conditions. Addressing these uncertainties and gaining a deeper understanding of the bolted flange joint behavior during hot bolting is vital for improving safety measures and operational efficiency.

This paper presents a comprehensive investigation into the behavior of bolted flange joints during the untightening of several bolts, while monitoring the load changes in the neighboring bolt of the flange connection using two untightening patterns for comparison: the sequential clockwise pattern and the criss-cross pattern. By identifying and analyzing key factors such as contact stress and bolt displacement, this research aims to provide valuable insights into investigating the hot bolting procedure.

To conduct this investigation, we utilized a NPS 4 class 900 class flange and tested three types of gaskets metal, teflon and graphite. These different gasket materials were chosen to examine their influence on the bolted joint elastic interaction and cross talk behavior under the given conditions. The experimental phase involved systematically untightening bolts using the two mentioned patterns while monitoring stress distribution, bolt displacement, and overall joint stability. The use of high-precision sensors and monitoring equipment allowed for accurate and detailed data collection throughout the procedure.

In addition to the experimental approach, the study employed finite element modeling (FEM) to validate the observed behavior. FEM simulations provided a deeper understanding of the mechanics involved, allowing us to visualize stress distribution and deformation patterns that were not easily observable in the experimental setup. The comparison between experimental and numerical results revealed a high degree of similarity, demonstrating the effectiveness of FEM as a predictive tool for hot bolting. Any differences between the two sets of results were carefully analyzed, and were explained in the context of the material properties and experimental constraints.

The paper also discusses the critical safety measures that must be implemented during hot bolting to prevent catastrophic accidents. Understanding how different gasket materials and untightening patterns influence the joint’s behavior allows for better planning and more effective risk management strategies. By providing an in-depth analysis of the joint response under various scenarios, this study aims to contribute to the development of safer and more efficient hot bolting procedures, ensuring that maintenance operations can be carried out with minimal risk and maximal efficiency.

Overall, the findings of this paper offer valuable insights into optimizing hot bolting practices, contributing to the broader body of knowledge in pressure vessel and piping maintenance.

keywords: hot bolting, bolted flange joints, untightening bolted flange joints, finite element modeling, pipeline safety, post construction maintenance, contact stress, elastic interaction.

Presenting Author: Ali Tofighi École de technologie supérieure

Presenting Author Biography: Ali Tofighi has both academic and professional experience in piping engineering. He previously worked on the desulfurization of gas oil project at Tabriz Refinery as a piping supervisor in the technical and executive offices. He also contributed to the design and modeling of pipelines for a refinery cooling system, which was part of his Bachelor’s final project in mechanical engineering at Urmia University.

Authors:

Ali Tofighi École de technologie supérieure
Linbo Zhu Xi'an Jiaotong University
Abdel-Hakim Bouzid École de technologie supérieure