Development of Weld Residual Stress Measurement Method for Primed Steels

Welding, as a major manufacturing process in shipbuilding, induces residual stress and distortion that affects buckling strength, fatigue performance, corrosion resistance, and dimensional stability of ship structures. Understanding residual stress in ship structures is required in engineering design to ensure structural strength and safety and is essential in dimensional accuracy for distortion control during fabrication. However, measuring residual stress in ship structures presents unique challenges, such as structure complexity, surface primer, and a non-friendly measurement environment. Fortunately, portable X-ray diffraction equipment has been successfully developed and proven accurate in other industries to measure residual stress. This study is to evaluate the feasibility of measuring residual stress in a shipyard environment in terms of accuracy and adaptability. Typical welded joints (butt joint and T-joint) were selected for evaluation instead of evaluating complicated ship structures. The welded joints were fabricated using common shipyard welding procedures. This makes the evaluation easier since weld residual stress distributions and magnitudes on these joints are well understood. In addition, the hole-drilling method was also used to validate the X-ray diffraction results. Measured results show that X-ray diffraction can penetrate the pre-construction surface primer used in shipbuilding to directly measure residual stress of the metal surface, without the need to remove the surface primer. The residual stress data measured by X-ray diffraction agreed with the data obtained by the hole-drilling method. In addition, the residual stress trend measured by X-ray diffraction agreed with the theoretical residual-stress distributions. This study concluded that a portable X-ray diffraction is a potential technology for residual stress measurement in a shipyard.