Issue 35

A. Mehmanparast et alii, Frattura ed Integrità Strutturale, 35 (2016) 125-131; DOI: 10.3221/IGF-ESIS.35.15 127 metal volume exists. Independent studies on welding residual stress measurements in multi-pass butt-welded austenitic stainless steel thick walled pipes presented in [6] and A36 structural steel thick plates shown in [7] confirm that the welding residual stress is severely sensitive to the yield strength of the weld metal. Figure 2 : Different scenarios of multi-pass weld runs examined in [5]. X Y Figure 3 : An example of a multi-pass welded plate. Figure 4 : Illustration of the plate thickness effects on post-welding residual stress distribution in Type 304 stainless steel [8]. A similar study was carried out on AISI Type 304 stainless steel in [8] where thin plates during multi-pass Manual Metal Arc Welding (MMAW) process were measured using X-ray diffraction. It has been shown in [8] that by increasing the number of passes in single V-groove welded plates, the magnitude of peak tensile stress (at the centre of the weld) gradually reduces and increases on the root side and the top side of the weld pads, respectively. Also shown in [8] is that increasing the thickness of the weld pads leads to an increase in the extent of the residual stress distribution region and a reduction in the peak tensile residual stress values (see Fig. 4). Numerical studies of pass-by-pass residual stress predictions in thick walled plates and thick walled stainless steel pipes can be found in the published literature (e.g. [9, 10]). For instance a finite element study to predict maximum residual stresses in K and V type multi-pass weld joints before and after post weld heat treatment was carried out by Cho JR et al [10] in which the predicted results were validated through comparison with hole drilling measurements. It has been shown in [10] that the post weld heat treatment can reduce the maximum residual stress values by around 15%.