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NDT-RAM Systems Selection Guide
Home > NDT > Comparison of Non-Destructive Testing Methods

Comparison of Non-Destructive Testing Methods

Resonant Inspection Compared to Other Non-Destructive Testing Techniques

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

Traditional NDT Technique Comparison

Excellent Excellent Fair Fair Poor Poor
Cracks/Chips/Voids Excellent Excellent Excellent Excellent Fair
Material Properties Excellent Poor Poor Poor Fair
Missed Operations Excellent Poor Poor Poor Poor
Structural Integrity Excellent Excellent Excellent Excellent Excellent
Product Lot Variation Fair Fair Excellent Excellent Excellent
Defect Location
Surface (External) Excellent Excellent Excellent Excellent Poor
Internal Excellent Poor Poor Excellent Excellent
Brazing/Bonding/Welding Excellent Poor Poor Fair Fair
Throughput Excellent Fair Fair Excellent Poor
Training/Certification  Excellent Poor Poor Poor Poor
Total Inspection Costs Excellent Fair Fair Poor Poor
Automation Capacity
Quantitative Results Excellent Poor Poor Fair Poor
Ease of Automation Excellent Fair Fair Poor Poor
Cost of Automation Excellent  Fair Fair Poor Poor Poor

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Resonant Inspection
Ultrasonic Testing
Eddy Current
Liquid Penetrant
(LPI / PT)
Magnetic Particle
(MT / MPI)
Infrared Thermography
Visual Inspection


Resonant Inspection is a whole-body test method which detects resonant frequency shifts resulting from changes in mass, stiffness or damping of a part. Resonance can detect defects such as cracks, voids, chips, brazing problems, nodularity, variations in hardness, missed manufacturing processes, delamination, and more.

Applications include, but are not limited to, powder metal parts, castings, ductile iron parts, brazed assemblies, forgings, stampings and ceramic parts.

Non-Destructive Testing Resonant Acoustic Method (NDT-RAM) is a form of resonant inspection offered by The Modal Shop. NDT-RAM is available in automated, semi-automated, manual, and small-part drop-test systems. Learn more about which system is right for you

Advantages Disadvantages
  • Whole body test for internal and external flaws
  • Fast testing time: 3 seconds per part (typical)
  • No part preparation or cleaning required
  • Objective pass/fail result
  • No consumables expenses
  • Easily automated
  • Easily integrated into manufacturing process
  • 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
  • Not diagnostic - does not indicate where flaw is, just there is one
  • Materials that resonate only - metal, composites and ceramic parts
  • Large parts (> 100 lbs.) difficult to test
  • Significant manufacturing process variations can mask defect detection

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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
  • Immediate results
  • Automation possible
  • Permanent record capability
  • Portable
  • High penetration capability
  • Couplant required
  • Complex, or small parts may be difficult to check
  • Defect may be missed if not in the path of the ultrasonic signal
  • Reference standards required
  • Trained operators for manual inspections
  • Special probes
  • Surface condition

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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
  • Portable
  • Geometry variation does not affect direction of radiation beam
  • Radiation hazard
  • Expensive
  • Trained operators needed
  • Linear defect may be missed
  • Depth of defect not indicated
  • Access to at least two sides of the part required

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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
  • Low cost
  • Permanent record capability
  • No couplant required
  • No probe contact required
  • Conductive material only
  • Shallow depth of penetration
  • Surface roughness may affect test quality

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Measures or detects defects open to the surface of parts such as cracks, porosity, seams, laps and through wall leaks.

Advantages Disadvantages
  • Low cost
  • Portable
  • Indications may be further examined
  • Defect must be open to the surface
  • Parts must be cleaned before and after testing
  • Surface films, such as coatings, scale, and smeared metal may visually mask defects

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Measures or detects surface and qualified subsurface defects, cracks, seams, porosity, inclusions, and very sensitive for locating small tight cracks.

Advantages Disadvantages
  • Low cost
  • Portable
  • Subsurface defects
  • Ferromagnetic materials only
  • Alignment of magnetic field is critical
  • Demagnetization required after the test
  • Surface coatings can mask defects
  • Pre and post cleaning necessary
  • Messy
  • Subjective: dependent on operator interpretation
  • Difficult to automate

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Measures or detects hot spots, heat transfer, temperature ranges, temperature monitoring and electrical assemblies.

Advantages Disadvantages
  • Permanent record or thermal picture
  • Remote sensing
  • Portable
  • Expensive
  • Reference standards required
  • Poor resolution on thick sections

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Measures or detects surface flaws, blemishes, missing features, and dimensional flaws.

Advantages Disadvantages
  • Generally fast test time
  • Can be automated
  • Good at finding dimensional flaws or surface blemishes
  • Portable
  • Reference standards required
  • May require multiple cameras and viewing angles for automated systems
  • Subject to operator interpretation if not automated

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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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