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Home > NDT > Comparison of Non-Destructive Methods

Comparison of Non-Destructive Methods

Applications
Below you will find a general outline of the capabilities of common nondestructive testing methods. This is intended as brief summary of each discipline's capabilities.

Quick Links: Resonant Inspection  Ultrasonics  Radiography
Eddy Current  Liquid Penetrant  Magnetic Particle  Infrared Thermography


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
As fast as 3 seconds per part 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 and 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 parts. 

Advantages Disadvantages
Permanent records Radiation hazard
Portable Expensive
Geometry variation does 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 and 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 may visually 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

Learn More
What is Non-Destructive Testing?
Resonant Acoustic Method
How the Equipment Works
Measurement and Detection Principles
Advantages of NDT-RAM™
Case Studies

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