Browsing by Author "Dunne, D"

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    HAZ cold cracking - a restrained view
    (Welding Technology Institute of Australia, 1994) Squires, IF; Feng, B; Mercer, D; Payten, WM; Dunne, D; Alam, N
    Heat affected zone (HAZ) hydrogen cracking occurs after the weld has cooled to ambient temperature when the HAZ has transformed and hydrogen has had time to diffuse into it from the weld metal. It is therefore referred to as “cold cracking”. For cracking to occur, a stress needs to be present This will arise inevitably from the local heating and cooling when making the weld, however, the magnitude of the stress will depend on the restraint applied to the weld, the welding conditions used and the geometry of the weld. Recommendations to assist with the avoidance of HAZ cold cracking are available in publications such as WTIA Technical Note 1 “Weldability of Steels” but these cover essentially only the control of the thermal cycle and hydrogen level. The more complex issue of restraint is not included. Consequently the recommendations tend to be either over conservative, hence not fully cost effective, or present unquantied risks. Research work by various authors in this area has been summarised by Suzuki(l) and a basic model produced. The work covered a variety of methodologies and these could not be considered consistent. The present study provides a consistent approach, based on the use of the rigid restraint cracking (RRC) test which allows direct measurement of weld stress. To enable the effect of local stresses to be understood and general models of restraint effects to be developed a finite element analysis (FEA) computer model is being developed in parallel with work on the RRC test Further inputs to the modelling process are being or will be generated from localised studies of mechanical properties in the weld and heat affected zone and from dilatometric studies of the weld. The former will allow more accurate assessment of the behaviour of local stress concentrators in the weld and HAZ. The latter will assist in quantifying the weld metal and HAZ contribution to stress generation.
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    The performance of an emergency cold weld repair on a 2.25Cr-1Mo longitudinally seam-welded pressure vessel
    (The Institute of Materials Engineering Australasia Ltd., 2004) Budzakoska, E; Dunne, D; Law, M; Li, HJ; Small, B
    This is an overview of a current three-year project for the Cooperative Research Centre for Welded Structures entitled “Integrity of High Energy Piping”. The results of a performance evaluation conducted on an emergency cold weld (controlled deposition temperbead, TB) repair applied to a 2.25Cr-1Mo steel header using the manual metal arc welding (MMAW) process are described. With repair rather than replace being a far more viable option, welding is increasingly used for performing repairs, replacements, retrofits and modifications to elevated temperature plants. However, with the considerable cost and time involved with performing conventional post weld heat-treatment (PWHT) repairs, in today’s economic environment utility owners are increasingly forced to turn toward other alternatives, such as cold weld repairs. These require no PWHT and rely on a controlled deposition process – precise weld bead placement and heat inputs etc to achieve tempering of the HAZ. However, much of the research conducted on these repair techniques has used accelerated high temperature creep testing to demonstrate their integrity. How well this reflects their real-life performance is unknown. Therefore this study provides an opportunity to evaluate the effects of service exposure on the performance of an emergency cold weld repair. © 2003, The Institute of Materials Engineering Australasia Ltd.
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    Simulation of HAZ sub-zone microstructures in P92 steel
    (9th International Conference and Exhibition 2009 Operating Pressure Equipment Incorporating the AINDT Biennial Conference, 2009-08-28) Sunjaya, D; Drew, M; Li, HJ; Dunne, D