Residual stress measurements in a ferritic steel/In625 superalloy dissimilar metal weldment using neutron diffraction and deep-hole drilling A. Skouras a, * , A. Paradowska c , M.J. Peel a , P.E.J. Flewitt b , M.J. Pavier a a Department of Mechanical Engineering, University of Bristol, Bristol BS8 1TR, UK b H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK c Australian Nuclear and Technology Organisation, DC NSW 2232 Kirrawee, Australia article info Article history: Received 15 June 2012 Received in revised form 16 November 2012 Accepted 27 November 2012 Keywords: Deep-hole drilling Residual stresses Neutron diffraction Dissimilar weld P92 In625 Texture abstract This paper reports the use of non-invasive and semi-invasive techniques to measure the residual stresses in a large dissimilar weldment. This took the form of a butt weld between two sections of a P92 steel pipe, joined using an In625 welding consumable. Residual stress measurements have been carried out on the 30 mm thick welded pipe using the deep-hole drilling technique to characterise the through wall section residual stress distribution for the weld metal, HAZ and parent material. In addition, neutron diffraction measurements have been carried out within the weld zone. Diffraction patterns presented a high intensity and sharp peaks for the base P92 steel material. However measurements in the weld superalloy material were proven problematic as very weak diffraction patterns were observed. A thor- ough examination of the weld material suggested that the likely cause of this phenomenon was texture in the weld material created during the solidification phase of the welding procedure. This paper discusses the challenges in the execution and interpretation of the neutron diffraction results and demonstrates that realistic measurements of residual stresses can be achieved, in complex dissimilar metal weldments. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Weldments in safety critical plants are subject to structural integrity assessments where residual stresses may play a key part [1,2]. In the case of engineering components operating at elevated temperature, the presence of tensile residual stresses can increase the likelihood of time dependent failure by acting as a driving force for the initiation and growth of cracks. There is a need to be able to measure the residual stresses arising from such a joining technique. Dissimilar welds are often used in service without heat treatment which means a knowledge of residual stress is even more impor- tant. Residual stress measurements provide both an improved understanding of the magnitude and origins of residual stresses in these complex dissimilar metal weldments as well as an improved basis for undertaking integrity assessments. Residual stresses are those stresses not required for an engi- neering component to maintain its equilibrium with the environ- ment [3]. Previous studies [4e6] have shown that residual stresses can have beneficial or detrimental effects. In all cases, knowledge of primary and residual stresses needs to be known when assessing the integrity of a structure [7]. Residual stresses are categorised based on the length scale over which they equilibrate [3]. Macro- stresses, Type I, vary over large distances and over several grain in a polycrystalline material. Meso-stresses, Type II, vary over the dimensions of individual grains. Stresses that fall below the Type II length scale, that are contained within individual grains are classed as Type III micro-stresses and usually arise due to dislocation stress fields or coherency at interfaces within the microstructure. Type I macro-stresses provide the principal elastic stored energy to give a driving force for damage creation and evolution. Types II and III stresses may also provide a contribution to specific parameters. A wide range of techniques is available for measuring stresses over different length scales. These techniques range from non- invasive to invasive and are capable of measuring stresses from the macro-scale down to the micro-scale. Examples of non-invasive techniques are X-ray diffraction and neutron diffraction [8]. In semi-invasive methods, analysis requires only small quantities of material to be removed, allowing further testing on the component. Examples of semi-invasive methods include center hole drilling [9], slotting [10] and the Sachs method [11]. Lastly, fully invasive measurement techniques involve the removal of large quantities of * Corresponding author. Tel.: þ44 (0)117 3315941. E-mail address: as6631@bristol.ac.uk (A. Skouras). Contents lists available at SciVerse ScienceDirect International Journal of Pressure Vessels and Piping journal homepage: www.elsevier.com/locate/ijpvp 0308-0161/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijpvp.2012.11.002 International Journal of Pressure Vessels and Piping 101 (2013) 143e153