Investigation of the elastic/crystallographic anisotropy of welds for improved ultrasonic inspections

Abstract

Ultrasonic inspection is an effective way of ensuring the initial and continued integrity of welded joints nondestructively. The accuracy of the technique can be compromised due to spatial variations in the anisotropy of the material stiffness in the weld region. Predicted in-plane weld stiffness maps can be used to correct the ultrasound paths for improved results, but these are based on several assumptions about the weld material. This study has examined the validity of these assumptions and provided detailed weld metal grain orientation maps from which a stiffness map has been calculated for an Inconel 600 weld. Good agreement was found except near the boundaries of the weld. Further it was found that the crystal growth (most compliant) direction was typically oriented around 14.5°out of plane towards the welding direction. Having validated the model, a comparison of predicted and calculated stiffness maps was made. The predicted map was found to be satisfactory over the majority of the weld area.

Nonintrusive estimation of anisotropic stiffness maps of heterogeneous steel welds for the improvement of ultrasonic array inspection

“…The material properties of the austenitic weld used in the experiment were determined using the Electron BackScatter Diffraction (EBSD)-based method, Orientation Distribution Functions (ODFs) were determined from the EBSD data and combined with the literature value for the single crystal stiffness tensor of monocrystal Fe-18%Cr [29]. The method is described in more detail in [10]. The calculated values are shown in Table 1; these are slightly different from the values from the literature that we used earlier.…”

“…The material properties were considered to be transversely isotropic, and symmetrically orientated with respect to the plane of the cross-section, so that a two dimensional model can be applied, however in reality the orientation of the polycrystal grains in the weld may be tilted slightly out of the plane [10]. A more accurate approach would be to consider the material properties of the weld to be orthotropic [30], and apply a three dimensional model to describe the weld map.…”

“…There is also an influence of the orientation of the component while the weld is being made, when gravitational forces can skew the alignment of the solidifying material; this has a particularly large effect when the weld is vertical. Nevertheless this simplifying assumption of material symmetry has been shown to be approximately correct from macrograph and Electron Back Scattering Diffraction (EBSD) measurements [10], and has been adopted widely [5,6,3,7,8,11].…”

Comparison of grain to grain orientation and stiffness mapping by spatially resolved acoustic spectroscopy and EBSD

“…Crystal orientation maps were measured by EBSD (Mark et al ., ) in a Camscan FEGSEM; see Figure . The region that can be mapped by scanning the beam in a scanning electron microscope is relatively small.…”

“…If there is no strong texture in the parent material, or if the parent material has a different structure (e.g. BCC steel such as P91), this growth behaviour would be expected to result in welds with essentially <100> fibre textures locally oriented to match the thermal gradients imposed by the weld passes (Mark et al ., ).…”