Weld Residual Stress Measurement on Ship Structures

Weld residual stresses on ship structures were significantly investigated by taking 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 SNAME-2017 conference, concluded that portable x-ray equipment can be used in a shipyard environment to provide reliable measurements. Residual stress measurements were successfully measured on small welded joints, DH36 panel, and HSLA-65 panel, but not on 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 least 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 paper reports the measured stresses on HSLA-80 panel, the tiedown, and the knuckle joints.