An Accurate Method of Evaluating Relaxation in Bolted Flanged Connections

[+] Author and Article Information
A. Bouzid, A. Chaaban

Department of Mechanical Engineering, Ecole Polytechnique, Case postale 6079, Succ. “C.V.” Montreal, Quebec, H3C 3A7 Canada

J. Pressure Vessel Technol 119(1), 10-17 (Feb 01, 1997) (8 pages) doi:10.1115/1.2842254 History: Received November 07, 1995; Revised April 04, 1996; Online February 11, 2008


Bolted flanged joint assemblies may begin to leak some time following a successful hydrostatic test. One of the reasons is that the gasket experiences a drop in its initial compressive stress due to creep, thermal dilatation, and thermal degradation. The need to pay attention to the relaxation behavior of bolted joints for high-temperature applications is recognized by the ASME Code, but no specific guidelines are given to help engineers, neither at the design nor maintenance levels. This paper deals with the basic analytical tools that have been used to develop a computer program “SuperFlange” that can be used to make accurate predictions of the relaxation of bolted flanged joints, and hence be able to provide a reasonable leakage assessment over time. A simplified analytical method of relaxation analysis will also be presented. These proposed methods are supported by test results obtained on a real bolted joint fixture and by FE modeling. A strong emphasis will be put on flanged joint rigidity, which is one of the major controlling parameters of relaxation besides the material properties involved.

Copyright © 1997 by The American Society of Mechanical Engineers
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