**1. Introduction**

Residual stresses in welded components develop during cooling due to expansion/ contraction hysteresis across the weld and the heat-affected zone. There are several ways to reduce or minimize the residual stresses. By proper pre-welding management and taking precautions, welding residual stresses can be eliminated or minimized to an acceptable level. This can be achieved by several techniques including but not limited to the following:


Not all the above variables apply to all welding processes and materials, but controlling the applicable parameters and use of proper welding process and sequence can effectively reduce welding residual stresses to acceptable levels.

Residual stresses can be present in the component even though proper actions were taken during welding to minimize the stress levels and can add to the applied stress, which causes the failure of the component. Although apparently, the applied stress is much less than the yield stress or design stress of the component, the component fails due to hidden residual stress which may add to the applied stress and can eventually lead to failure under normal operating stresses. Most of the earlier development to measure the amount of residual stress are destructive in nature which means cutting the component at several strategic locations thus making the component unusable for the intended purpose. This is a more complicated onsite fabrication process where there is no provision to cut the component to determine the residual stresses because the component will then become unusable. Sometimes the large size of the structures precludes the destructive way of determining the residual stresses. Hence the development of non-destructive measurement of residual stresses comes into considerations. Most commonly, non-destructive measurement of residual stresses is typically done using Xray diffraction (XRD) and/or neutron diffraction (ND). However, these methods are generally not portable, and XRD is limited to near-surface measurements because of the short penetration depth of X-rays in metals (101 μm). Therefore, there is a strong interest in exploiting alternative technologies for residual stress characterization in engineering components. Developments in ultrasonic, eddy current, and thermal-optic residual stress measurement techniques to determine their feasibility as field-deployable characterization tools makes the approach to detect and measure residual stresses in the welded components easier and reliable. One of the recent developments of nondestructive measurement of residual stresses is the Magnetic Berkhausen Noise technique (MBN). Here, we will discuss the principles and advances in non-destructive techniques, particularly the MBN technique.
