Non-Destructive Test
Comparison of NDT MethodsA comparison of different NDT methodsApplications
Below you will find a general outline of the capabilities of some common nondestructive testing methods. This is intended as brief summary of each discipline's capabilities.
RESONANT INSPECTION
Detects resonant frequency shifts resulting from changes in mass, stiffness or damping of a part. Defects such as cracks, voids, chips, brazing problems, nodularity, porosity, variations in hardness, missed manufacturing processes, and delamination can be detected.
Applications include powder metal parts, ductile iron parts, brazed assemblies, forgings, stampings, and ceramic parts.
| Advantages |
Disadvantages |
| Whole part test for internal and external flaws |
Not diagnostic does not indicate where flaw is, just there is one |
| Fast as 1 part per second |
Materials that resonate only - metal, composites and ceramic parts |
| No part preparation required |
Large parts (> 60lbs) difficult to test |
| Objective pass/fail result |
Significant lot to lot variations can mask defect detection |
| No consumables expenses |
|
| Easily automated |
|
| Permanent record capability |
|
| Easily finds first n number of natural frequencies for NVH applications |
|
| Best for high volume quality inspection |
|
| Designed to be on the plant floor |
|
ULTRASONICS
Measures thickness, velocity, or detects internal defects and variations, such as cracks, lack of fusion, delaminations, lack of bond.
Applications include, wrought metals, welds, brazed joints, adhesive or bonded joints, non-metallic materials, in-service parts.
| Advantages |
Disadvantages |
| Most sensitive to cracks |
Couplant required |
| Immediate results |
Complex, or small parts may be difficult to check |
| Automation possible |
Reference standards required |
| Permanent record capability |
Trained operators for manual inspections |
| Portable |
Special Probes |
| High penetration capability |
Surface condition |
RADIOGRAPHY
Measures or detects, internal defects and variations, porosity, inclusions, cracks, lack of fusion, corrosion, geometry variation, density changes, misassembled, and misaligned.
| Advantages |
Disadvantages |
| Permanent records |
Radiation hazard |
| Portable |
Expensive |
| Geometry variation do not effect direction of radiation beam |
Trained operators needed |
| |
Linear defect may be missed |
| |
Depth of defect not indicated |
| |
Access needed to at least two sides of the part |
EDDY CURRENT
Measures or detects surface and subsurface cracks and seams, alloy content, heat treatment variations, wall and coating thickness, crack depth, conductivity, and permeability.
| Advantages |
Disadvantages |
| High speed |
Conductive material only |
| Low cost |
Shallow depth of penetration |
| Permanent record capability |
|
| No couplant required |
|
| No probe contact required |
|
LIQUID PENETRANT
Measures or detects defects open to the surface of parts such as cracks, porosity, seams, laps, through wall leaks.
| Advantages |
Disadvantages |
| Low cost |
Defect must be open to the surface |
| Portable |
Parts must be cleaned before and after testing |
| Indications may be further examined |
Surface films, such as coatings, scale, and smeared metal visually may mask defects |
MAGNETIC PARTICLE
Measures or detects surface and qualified subsurface defects, cracks, seams, porosity, inclusions, and very sensitive for locating small tight cracks.
| Advantages |
Disadvantages |
| Low cost |
Ferromagnetic materials only |
| Portable |
Alignment of magnetic field is critical |
| Subsurface defects |
Demagnetization required after the test |
| |
Surface coatings can mask defects |
| |
Pre and post cleaning necessary |
| |
Messy |
INFRARED THERMOGRAPHY
Measures or detects, hot spots, heat transfer, temperature ranges, temperature monitoring, and electrical assemblies.
| Advantages |
Disadvantages |
| Permanent record or thermal picture |
Expensive |
| Remote sensing |
Reference standards required |
| Portable |
Poor resolution on thick sections |
|
