Weld Residual Stress Measurement on Ship Structures

Abstract

Weld residual stresses on ship structures were significantly investigated by using a three-step approach. Step 1 is to measure residual stress on small samples in laboratories to validate measurement methods, step 2 is to measure residual stress on three test panels made of DH36, HSLA-65, and HSLA-80 in a shipyard, and step 3 is to measure residual stress on a large mock-up unit and on a tie-down. Step-1 and step-2 study, presented in the Society of Naval Architects and Marine Engineers-2017 conference, concluded that portable X-ray equipment can be used in a shipyard environment to provide reliable measurements. Residual stress was successfully measured on small welded joints, the DH36 panel, and the HSLA-65 panel, but not on the HSLA-80 panel. The reason for poor measurements on the HSLA-80 panel was that the primer on HSLA-80 surfaces blocked the diffracted X-ray. To achieve a good measurement, mechanical grinding and electropolishing were investigated to remove the primer before measurement. The minimum electropolishing time required to remove the compressive stress induced by mechanical grinding was established by experimental trials. With the electropolishing process, reasonable measurements were achieved on the HSLA-80 panel, a tie-down, and the knuckle joints of the large mock-up unit. This study reports the measured stresses on the HSLA-80 panel, the tie-down, and the knuckle joints. Welding, as one of the most important manufacturing processes in shipbuilding, inevitably induces residual stress and distortion on ship structures. Multiple methods have been developed to measure residual stress with nondestructive and destructive techniques. The common nondestructive techniques include X-ray diffraction (XRD) (Gou et al. 2015; Bandyopadhyay et al. 2018; Monine et al. 2018), neutron diffraction (Palkowski et al. 2013), magnetic method, ultrasonic methods (Bray & Junghans 1995), and impact-indentation method (Zhu et al. 2015). The destructive techniques include hole-drilling and ring-core methods, and the destructive techniques include block removal, splitting, layering, and contour methods (Leggatt et al. 1996).