Wrought brass parts are prone to stress corrosion cracking in a corrosive environment if the stress-relief annealing is not properly conducted. Therefore some accelerating test methods are generally adopted in the laboratory to evaluate the stress corrosion cracking resistance of metal parts. However in the ammonia vapor test such as ASTM B 858 questions about the test failure sometimes arise for the judgment of indistinct cracks. The corrosion byproducts covered on the tested metal part enhance the irregularity of metal surface so that distinguishing the initiation of true cracks from a mark resulted from the drawing die becomes challenging. In this study ball valves made of forge brass were subjected to ammonia vapor tests with various severities and then examined for the cracks with optical microscopy and X-ray computed tomography (CT). Typical stress-corrosion cracks perpendicular to the direction of applied stress on brass valves could be observed on failed samples but cracks tended to become tiny and shallow while reducing the corrosiveness of testing environment. With the X-ray CT technique micro cracks on brass valves were observed and their depth and direction could also be check non-destructively. Further metallography and EDS analysis verified the results obtained from CT scan.