This document discusses non-destructive testing (NDT) techniques. It defines defects as any departure from specified material requirements that can reduce service life. Common defects include cracks, surface defects, blow holes, porosity, and slags. Visual inspection and borescopes are described as visual NDT methods. Acoustic emission testing detects cracks and corrosion by measuring ultrasonic pulses emitted during stress testing. Liquid penetrant testing is used to detect issues like corrosion, weld discontinuities, cracks, fractures, leaks, and misalignments.