Circumventing Practical Difficulties in Determination of Threshold Stress Intensity for Stress Corrosion Cracking of Nar
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INTRODUCTION
A. Aim
STRESS corrosion cracking (SCC) of welded reaction vessels is an ongoing and common concern in the alumina industry. Welded reaction vessels (e.g., digesters, precipitators, and evaporators) of mild steel when exposed to hot caustic solutions in the Bayer process for the extraction of alumina from Bauxite ores often suffer from SCC.[1–4] Often, SCC failure in pipes and vessels is more prevalent in their welded sections primarily because welding introduces residual stresses as well as surface defects that induce SCC crack initiation and propagation. The threshold stress intensity for stress corrosion cracking (KIscc) data is not only necessary for the design of welded structures for corrosive environment, but also an accurate determination of KIscc is invaluable for the accurate life prediction of aged welded components. The aims of the current study are as follows: To determine the KIscc of narrow welded sections To validate a recently established technique (i.e., cir-
cumferential notch tensile [CNT] testing) for the determination of KIscc of narrow sections such as welds and heat-affected zone (HAZ) SARVESH PAL, formerly PhD Student, with the Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia, is now Postdoctoral Fellow with the School of Mechanical and Mining Engineering, The University of Queensland, Brisbane, QLD 4072, Australia. R.K. SINGH RAMAN, Professor, is with the Department of Mechanical and Aerospace Engineering, Monash University, and is also with the Department of Chemical Engineering, Monash University, Clayton, VIC, Australia. Contact email: [email protected] R. RIHAN, formerly PhD Student, with the Department of Mechanical and Aerospace Engineering, Monash University, is now Research Academic with the Center for Engineering Research, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia. Manuscript submitted April 20, 2011. Article published online March 17, 2012 3202—VOLUME 43A, SEPTEMBER 2012
To produce linearly elastic fracture mechanics vali-
dated KIscc data B. KIscc of Microstructurally Narrow Regions An accurate determination of the KIscc of narrow sections of weld and HAZ is a challenge because of the requirements of large specimens for the traditional techniques and difficulty in restricting crack propagation to narrow regions in such specimens. As a result, fewer studies have been devoted to KIscc of weldments.[5–8] C. Techniques to Determine KIscc Center cracked (CC), surface flawed, cantilever bend, double-cantilever beam (DCB), and compact tension (CT) are the common specimen geometries that have been used traditionally for the determination of the SCC susceptibility and the KIscc of metals and alloys.[9] However, these techniques are fraught with limitations, namely (1) the specimens are prohibitively expensive to manufacture[9] and (2) a large cross-section of test materials is required. Such restrictions may limit the use of the traditional techniques for some cr
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