Residual Stress Characterization in Thick STE460 Steel Welding Seam Using Neutron Diffraction

The residual stress within the weld is a key factor affecting the safety and the life performance of welded pipelines. The only method to validate structural integrity in thick steel welds nondestructively is neutron diffraction. Therefore, the residual stress distribution of a tungsten inert gas weld in a 40 mm thick pipe made of STE460 steel was investigated using neutron diffraction. In addition, microscopy and hardness measurements were used to analyze morphology and microhardness. The results show high residual stress up to 670 MPa in the weld, reaching nearly the ultimate tensile strength of STE460 steel, whereas only moderate residual stresses are found in the heataffected zone. Analysis of the width of the reflection profiles (full width at half maxima) indicates a low degree of plastic deformation in the weld region. The grain of the whole weld is almost uniform fine crystal grains in different areas. The hardness across the weld and through weld are quite homogenous, with hardness values in the range of （200-250）HV0.2. This kind of welded pipe fittings is widely used for foundation structures of wind power plants and transport of oil and gas. The results not only meet engineering requirements, but also will be used to calibrate devices for nondestructive evaluation methods like magnetic Barkhausen noise, ultrasonic and eddy current testing, which are used for the residual stress and crack detection in the industrial process. Furthermore, these results can increase understanding of STE460 steel thick section welds.