An extensive study was conducted on A516 grade 70 steel to investigate the effect of shallow cracks in weldment HAZs. This program was a cooperative effort with the University of Kansas sponsored by PVRC Committee on Failure Modes.Charpy V-notch (CVN) and crack-tip opening displacement (CTOD) tests were utilized to characterize the fracture toughness behavior of the heat-affected zone (HAZ) of A516-70 SMAW weldments. Initial tests were conducted on thermally simulated HAZ specimens. Specimens for CVN and CTOD tests were also extracted from weldments fabricated utilizing different weld procedures to confirm the results obtained from the thermally simulated HAZ specimens.The test results are explained on the basis of microstructural features in the HAZ and fractographic examination. Optical light microscopy (OLM) and scanning electron microscopy (SEM) were used for these evaluations. A computer-assisted imaging system was also utilized and it proved to be a powerful tool for fracture surface analysis. It was possible to predict toughness of actual weldment HAZ specimens by determining the area fractions corresponding to ductile tearing and cleavage. In addition, a linear correlation between the CTOD and/or CVN-absorbed energy and depth of the ductile zone and the areal percentage encompassed by the brittle region was found.