The J-contour integral value was determined by the method of direct evaluation on a pressure vessel with an axial crack in a welded specimen. The specimen, cut from a weldment made by manual-arc welding, was machine-notched and fatigue precracked. It was mounted by welding on the pressure vessel, positioned in the opening cut on the cylindrical shell. The test was performed by gradually increasing water pressure. Crack mouth opening displacement (CMOD) was measured by clip gage, and strains were measured by strain gages, positioned along the J-integral path. J-integral, CMOD, and hoop stress are presented as a function of applied pressure. The fatigue crack length was extended by approximately 10 mm during pressurization. The development of an experiment to determine the J_R curve in a full-scale test and to predict the residual strength of a cracked pressure vessel is considered.