Comparison of Non-Destructive Testing Methods

Excellent

Fair

Poor

	RAM Resonant Acoustic	ET Eddy Current	MT/PT Magnetic/ Penetrant	UT Ultrasonic	RT Radiography
Defect/Issue
Cracks/Chips/Voids
Material Properties
Missed Operations
Structural Integrity
Product Lot Variation
Defect Location
Surface (External)
Internal
Brazing/Bonding/Welding
Speed/Training/Cost
Throughput
Training/Certification
Total Inspection Costs
Automation Capacity
Quantitative Results
Ease of Automation
Cost of Automation

 

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Resonant Inspection (RI)	Ultrasonic Testing (UT)	Radiography (RT)	Eddy Current (ET)
Liquid Penetrant (LPI / PT)	Magnetic Particle (MT / MPI)	Infrared Thermography	Visual Inspection (VT)

 

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RESONANT INSPECTION (RI)
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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ULTRASONIC TESTING (UT)
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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RADIOGRAPHY (RT)
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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EDDY CURRENT (ET)
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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LIQUID PENETRANT (LPI / PT)
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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MAGNETIC PARTICLE INSPECTION (MT/ MPI)
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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INFRARED THERMOGRAPHY
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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VISUAL TESTING (VT)
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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