Inspection, Testing, and Quality Control
Core Concepts
Know nondestructive examination methods - visual (VT), liquid penetrant (PT), magnetic particle (MT), ultrasonic (UT), and radiographic (RT) - with their capabilities and limitations. Visual inspection is the most common and catches surface defects; PT finds surface-breaking defects on nonporous materials; MT works only on ferromagnetic materials; UT detects internal flaws and requires access to one side; RT reveals internal porosity and inclusions but poses radiation hazards. Destructive tests include bend, tensile, nick-break, macroetch, and impact tests. Understand weld discontinuities versus defects, acceptance criteria in codes, weld mapping, and documentation.
Traps
Watch for method limitations: PT cannot find subsurface flaws; MT fails on aluminum and austenitic stainless. RT is best for volumetric flaws, UT for planar flaws. Confusing a discontinuity (any interruption) with a defect (rejectable) is common.
Worked Example / Rule of Thumb
Selection rule: surface-breaking on nonmagnetic material → PT; surface-breaking on ferromagnetic steel → MT; internal volumetric flaws → RT or UT. A guided-bend test passing both face and root bends is a standard qualification acceptance check.