NDT

NDT, short for non-destructive testing, is a collective term for methods used to evaluate the properties and integrity of materials, components, or assemblies without causing damage or permanently altering their use. NDT aims to detect defects, measure dimensions, characterize materials, or monitor condition in service, supporting safety, quality, and reliability across industries such as aerospace, automotive, energy, construction, and manufacturing. The term is sometimes used interchangeably with non-destructive evaluation (NDE), though in some contexts NDE emphasizes the evaluation aspect.

Common NDT techniques include ultrasonic testing, which uses high-frequency sound waves to reveal internal flaws and to measure thickness; radiographic testing, using X-rays or gamma rays to image internal features; magnetic particle testing, which detects surface and near-surface defects in ferromagnetic materials by magnetization and the visualization of iron particles; liquid penetrant testing, where a visible or fluorescent dye reveals surface openings after a penetrant is applied and drawn out; eddy current testing, based on electromagnetic induction to detect cracks and assess material properties, especially near the surface in conductive materials; visual inspection, the simplest method, aided by lighting, magnification, or cameras; and acoustic emission testing, which monitors transient stress waves produced under load to identify active defect growth. Other methods include thermography and leak testing as appropriate.

An NDT program typically involves planning, selecting appropriate methods, performing inspections, interpreting results, and documenting findings. Personnel are trained and certified to levels (often Level 1, Level 2, or Level 3) under standards such as ISO 9712 or regional schemes like the ASNT SNT-TC-1A. Selection of method depends on the material, geometry, defect type, and service conditions, with acceptance criteria defined by codes and standards.

Safety and regulatory considerations include radiation protection for radiographic testing, proper handling and disposal of penetrants, and safe equipment operation. The development of NDT dates back to the discovery of X-rays in 1895, followed by advances in magnetic and ultrasonic techniques in the mid-20th century, with ongoing standardization and technological refinement since.