The effect of environmental medium on fatigue life for u-shaped bellows expansion joints

https://doi.org/10.1016/j.ijfatigue.2005.04.004Get rights and content

Abstract

As experimental research, the effect of environmental medium on corrosion fatigue life has been proposed in this paper. The research proves the fact that the presence of corrosive medium will accelerate both crack initiation and propagation rates and reduce the failure life for the expansion joints. Furthermore, an important suggestion should be made that the effect of environmental medium on fatigue life must be paid more attention to when dealing with fatigue analysis for bellows expansion joints.

Introduction

Bellows expansion joints as an element for compensating deformation are subjected to axial load from thermal deformation and often work under corrosive media. Because some local regions of bellows with high elastoplastic strain undergo cyclic loadings caused by start-up and shut-down and changeable operating conditions, they will be ruptured by corrosion fatigue. For years researches have been conducted on low cycle fatigue life for bellows expansion joints, of which the most authoritarian is EJMA [1]. It shows not only the counting formula but also the fatigue curve of bellows expansion joints made of austenitic steel. In recent years, some developments have been achieved in the failure analysis and prevention of corrosion fatigue cases, considering the effect of environment media on the fatigue life of austenitic components [2], [3], [4], [5], [6], [7]. Linder and Melander [8] pointed out that corrosion fatigue strength in 3% NaCl for the stainless steels investigated was found to be reduced by approximately 30–40% compared to fatigue strength in air.

This paper aims to analyze the effect of environmental medium on fatigue life for bellows expansion joints. The result of the experiment research shows that the rates of crack initiation and propagation will be stepped up and fatigue life for expansion joints reduced due to the existence of corrosive media. When dealing with the material, fatigue life is not the only judging standard, and anti-corrosion ability should be taken into account.

Section snippets

Test

At present, austenitic stainless steel is widely used in making bellows expansion joints in the world, because this kind of material has the superior synthetic characteristics of high strength, weld, cold deformation and oxidizing ability of heat resisting. Bellows expansion joints are usually installed in the heating system of steam and water with high temperature; because dead area, condensation and deposit provide for ion Cl- an opportunity to become potential harmful concentrates, there is

Test results

2-D axisymmetric finite element analysis was performed to investigate the detail stress distribution of bellows expansion joint. The finite element mesh of analysis model was shown in Fig. 4.

In order to correlate the result of finite element analysis with that of experiment, elastic rule of material were used. The displacement boundary conditions used in the analysis were that the nodes attached to one end of joint were fixed and the nodes attached to the other end was specified δ=4.15 mm in the

Conclusion

  • (1)

    Existence of corrosive media will reduce fatigue life for metal bellows expansion joints. The effect environmental medium should be paid more attention to when dealing with fatigue life for bellows expansion joints. Attention to mechanical loading only would be dangerous, and measures should be taken in material choosing, medium treatment and different types of expansion joints.

  • It is suggested that proper material be selected according to operating medium. Experimental research is expected to

References (10)

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