Methods and devices are provided for detecting, corrosion and cracks in fastener nuts. In an exemplary embodiment, an apparatus can be configured to couple to a fastener nut to facilitate inspection of the fastener nut for detection of flaws in the fastener nut, such as corrosion and cracks. The apparatus can be configured to couple to the fastener nut when the fastener nut is mounted on a fastener and in use in a larger system such as a subsea drilling apparatus or other system in which fasteners with fastener nuts attached thereto are used. The apparatus can include an ultrasonic probe configured to facilitate inspection of the fastener nut using ultrasonic waves.