Non-destructive evaluation (NDE) services
What is non-destructive evaluation?
NDE refers to sensing, imaging and various other analytical techniques that can be used to assess the quality of materials, components and structures without damaging or destroying them, saving money and resources. These advanced material evaluation services encompass non-destructive testing (NDT), condition monitoring and some areas of quality control and process monitoring.
What is the difference between NDE and NDT?
The terms NDE and NDT are often used interchangeably. However, NDE is a broader term than NDT, which typically focuses on the determination of mechanical properties only. NDE takes things a step further, evaluating the test results and their significance in combination with other data to provide a more comprehensive assessment of a material’s properties and structural health.
Our NDE services
We offer a wide range of NDE services across NPL. These include both direct application of NDT methods to materials in industry and a diverse array of complementary NDE techniques.
NDT for advanced engineering materials
We offer a broad choice of NDT techniques, including ultrasonic, optical, thermographic, X-ray and electrical and magnetic induction testing methods, as well as microwave imaging.
Find out more about non-destructive testing of advanced materials
.jpg)
Our NDE services
Ultrasonic evaluation techniques
NPL has a suite of ultrasonic equipment to cover a range of part sizes, including contact probes, scanning acoustic microscopy (SAM) and C-scan water tank immersion.
Ultrasound
- Scope/range: Contact probes (1-30 MHz compression and/or shear wave probes), low frequency 54 kHz probes, SAM (minimum spatial sampling 5 µm, beamwidth 120 µm), C-scan (0.5-50 MHz probes, inspection area 650 x 650 mm).
- Measured parameters: Time of flight, amplitude.
- Derived parameters: Thickness and intensity maps, cross-sections, defect detection (cracks, voids, porosity, delaminations), sample thickness, ultrasonic velocity.
- Suitability: Handheld contact probes, non-contact water bath inspections, spot measurements or mapping, volumetric interrogation. Flat, rotational and programmable surface-following scans.
Optical evaluation techniques
We offer a variety of optical methods, including laser shearography, digital image correlation and stereo line-scan measurement.
Laser shearography
- Scope/range: Heat, vacuum, pressure and direct loading techniques available. Large range of shear vectors and magnitudes possible depending on camera lens and desired resolution, from 1 to 180°.
- Measured parameter: Maps changes in the out-of-plane displacement gradient of a surface due to an applied stress.
- Derived parameter: Defect detection – voids and delaminations.
- Suitability: Non-contact large area imaging, surface or near-surface defects, applicability and depth penetration depends on the material.
Digital image correlation (DIC)
-
Scope/range: Measurement of external surface deformations of an object by capturing differences between ‘before’ and ‘after’ images. Can monitor objects ranging in size from micrometres (using scanning electron microscopy) to kilometres using panoramic image capture techniques with resolutions to 1/20 of a pixel.
- Measured parameters: Surface deformation, in-plane displacements (height, if using 3D DIC) and in-plane strain and shear, which can be caused by thermal or mechanical changes to an object. Additions and subtractions to a surface, like corrosion or loss of material caused by weathering or damage.
- Derived parameters: Full field displacement and strain, full field correlation coefficient (similarity measurements).
- Suitability: Generally, non-contact standoffs, depending on imaging modality and optical setup. Can use any wavelength. Resolutions typically subpixel to one-twentieth of a pixel. Can generate image panoramas >250 gigapixels. Efficient image processing solutions for large image sets, including:
- in situ structural measurements of nuclear facilities and decommissioning structures;
- condition monitoring of the interior of railway tunnels;
- detection of surface and sub-surface structural faults in brickwork and concrete structures;
- the effect of loading on road bridges;
- vibration and movement in oil and gas processing;
- fire damage to piers;
- residual stress measurement at the micrometre scale;
- crack propagation during mechanical testing;
- fatigue material coupons;
- fixture movements during testing; and
- large-scale mechanical testing in the laboratory.
Find out more about condition monitoring
Stereo line-scan measurement
- Scope/range: Variant of DIC using a pair of accurately aligned line-scan cameras to capture height maps as well as images. Fields of view range from tens of millimetres to several metres, with resolutions from micrometres upwards. Ideal for surveying large structures such as tunnels, rotating objects and production lines.
- Measured parameter: Images and height perpendicular to the surface and in direction of line of view.
- Derived parameters: Images and height maps built up of lines by moving perpendicular to line scan. Accurate repositioning allows comparison of differential line scan height maps to determine differences in height or shape.
- Suitability: Works well for evaluating tunnel walls using trolley- or train-mounted cameras, cylindrical storage units – such as in nuclear decommissioning – and objects on production lines.
Thermography techniques
This non-contact technique can be used to detect sub-surface features and some types of failures at temperatures close to ambient, without destructively cross-sectioning the objects under study.
Flash, long pulse and lock-in thermography
- Scope/range: Flash (millisecond duration), long pulse (~10 s) and lock-in (sine/square wave) excitations.
- Measured parameter: Heat flow/cooling of sample.
- Derived parameter: Defect detection – voids, delaminations, layer thickness.
- Suitability: Non-contact large area imaging, typically surface or near surface. Penetration depends on the material and surface quality.
Radiography evaluation techniques
X-ray analysis of an object – here with 2D images – allows measurement of the geometry of a material’s internal and external features without the need to disassemble a component.
2D X-ray
- Scope/range: 110 kV source with digital scanning bed, 83 µm resolution.
- Measured parameter: Absorption/penetration of radiation.
- Derived parameter: Defect detection – voids, cracking, porosity.
- Suitability: Non-contact, but uses ionising radiation so is confined to a cabinet with associated sample size limitations (~200 x 200 mm). Volumetric interrogation.
Microwave imaging techniques
Microwave imaging exploits the dielectric properties of materials to provide information on the internal structures of samples, as well as check for voids, delamination and water ingress.
2D microwave scanning
- Scope/range: 10.5 GHz (λ ~3 cm), 24.1 GHz (λ ~1.3 cm), and 34.0 GHz (λ ~0.9 cm) probes.
- Measured parameter: Changes to superposed amplitudes of standing waves due to differences in dielectric constant.
- Derived parameter: Defect detection – voids, delaminations.
- Suitability: Non-contact, large area imaging (x/y scanning table). Non-conductive samples only. Volumetric interrogation.
Eddy current and magnetic induction techniques
Eddy current and magnetic induction testing techniques are frequently used to evaluate coating thicknesses and defects in different materials.
Eddy current testing
- Scope/range: 60 kHz conductivity testing, 0.5-1 MHz and 4-6 MHz probes.
- Measured parameter: Changes to eddy currents induced in the material.
- Derived parameters: Crack detection in metallic/conductive samples. Non-conductive layer thickness.
- Suitability: Contact point measurements, orientation and probe handling are very important. Requires a conductive material.
Eddy current and magnetic induction methods
- Scope/range: Multiple probes for magnetic and eddy current-based thickness measurements, as well as duplex coating measurements.
- Measured parameter: Stand-off distance to underlying magnetic or conductive substrate.
- Derived parameter: Coating layer thickness measurement on metallic or ferromagnetic substrates.
- Suitability: Contact point measurements, requires initial calibration curve determination. Suitable for many coating/substrate material combinations.
Complementary NDE services
Ultrasonic techniques
Additional NDE ultrasonic techniques are available to complement the NDT ultrasonic methods.
Resonant ultrasound spectroscopy (RUS)
- Scope/range: 5 kHz to 10 MHz frequency sweep.
- Measured parameters: Resonant frequency peak detection, characteristic spectrum from resonant peaks.
- Derived parameter: Elastic engineering properties of anisotropic materials using inverse analysis methods.
- Suitability: Contact, whole-body resonance of small volumes with well-defined geometry, suitable for any non-lossy materials (such as metals and ceramics).
Impact excitation
- Scope/range: 10-200 kHz frequency range.
- Measured parameter: Fast Fourier transform analysis of the acoustic signal from an impacted component or model specimen, detected by microphone.
- Derived parameters: Elastic engineering properties of regular geometry isotropic materials, instrumented ‘tap’ NDT test for any component or material.
- Suitability: Contact, point measurements, manual or electromagnetic striking possible, comparative assessment for NDT purposes.
Optical techniques
Light-based measurement methods can be used to provide high-resolution surface and sub-surface data, enabling detailed characterisation of geometry, texture and material properties without physical contact.
Surface topography measurement
- Scope/range: Measurement of external surface topography of objects with nominally primitive forms ranging from millimetres to metres in size.
- Measured parameters: 3D surface topography, height maps on standard 2D grids, advanced scanning strategies possible.
- Derived parameters: Surface texture, form and waviness, surface roughness, profile and areal parameters.
- Suitability: Contact and non-contact systems, point, line and area scanning methods, off-line, in-line and on-machine capability. Traceability to the metre. Many data post-processing options for feature/defect detection and dimensional measurement.
2D optical imaging
- Scope/range: Contrast-optimised 2D optical imaging of external surfaces of objects. Broad dynamic range for objects from millimetres to metres in size.
- Measured parameters: 2D images at various magnification levels, with wide range of resolution and pixel sampling. Pixel bit depths up to 16 bit in greyscale. Wide range of optics for illumination and collection.
- Derived parameters: Lateral dimensions, spatial distribution of features.
- Suitability: Non-contact systems, point, line and area scanning methods, off-line, in-line and on-machine capability. Traceability to the metre for lateral scales. Many data post-processing options for feature/defect detection and dimensional measurement.
Thickness mapping
- Scope/range: Optical measurement of the thickness of objects with nominally planar geometry, ranging from micrometres to millimetres in size.
- Measured parameters: 3D surface topography of opposite faces of an object in a single coordinate system. Coating and multilayer thickness measurement possible for some material systems.
- Derived parameter: Thickness, coating thickness.
- Suitability: Non-contact system. Point scanning methods. Off-line, in-line and on-machine capability. Traceability to the metre. Many data post-processing options for feature/defect detection and dimensional measurement.
Thermometry
NPL offers both contact and non-contact thermometry services.
Non-contact thermometry
Includes radiation, phosphor, fibre optic and acoustic thermometry, plus quantitative thermal imaging.
- Scope/range: -196 to +3,000 °C.
- Measured parameter: Apparent radiance temperature.
- Derived parameter: Surface temperature.
- Suitability: Non-contact, requires an observation path to the target surface.
Contact thermometry
Thermocouples and resistance thermometers.
- Scope/range: -196 to +3,000 °C.
- Measured parameter: Surface temperature.
- Derived parameter: Surface temperature.
- Suitability: Contact, surface adhesion of a thermometer required.
Find out more about temperature measurement
X-ray techniques
NPL’s services for identification and measurement of subsurface defects include:
- quantification of localised differences in attenuation under X-ray illumination;
- establishing the limits of resolution and X-ray penetration for different materials;
- determining the effect of surface roughness on dimensional measurements;
- identification of interfaces within the component; and
- reviewing different tomographic techniques for 3D reconstruction.
X-ray computed tomography (XCT)
- Scope/range: Up to 225 kV. Volumetric imaging of samples up to 180 x 180 x 180 mm in size, with up to 3 μm resolution.
- Measured parameter: X-ray attenuation.
- Derived parameter: Non-contact, non-destructive volumetric visualisation.
- Suitability: Non-contact, non-invasive. Provides volumetric data. Can be used for form, thickness, distance, surface texture, structure and defect evaluation.
Find out more about X-ray computed tomography
2D radiography
- Scope/range: 2D imaging of samples up to 400 x 400 mm, with up to 3 μm resolution.
- Measured parameter: X-ray attenuation.
- Derived parameter: 2D non-contact.
- Suitability: Non-contact projection images. Used for defect inspection.
Electrical conductivity and resistance evaluation techniques
These methods assess how materials conduct electricity, offering insights into composition, heat treatment state and the presence of defects or stresses.
AC (eddy current) conductivity
- Scope/range: 2 to 60 MS/m (3.45 to 103 % IACS), 10 to 100 kHz. UKAS accredited at 60 kHz, in accordance with BS EN 2004-7.
- Measured parameter: AC (eddy current) conductivity.
- Derived parameters: Supply and calibration of reference materials. Calibration of AC conductivity instruments.
- Suitability: Contact used to determine the state of heat treatments and the effects of work on the hardening of materials/components in service. Used for detection of surface defects such as cracks (rail) and gives insights into other material effects, including stress.
DC conductivity
- Scope/range: Performed using a range of 4-point probe techniques. 1 to 60 MS/m (3.45 to 103 % IACS). UKAS accredited in 2023.
- Measured parameter: DC (bulk) resistivity.
- Derived parameter: Resistivity of bars, block, wires, etc.
- Suitability: Contact technique supporting material characterisation for the materials above in accordance with ASTM and MIL standards.
Terahertz and microwave evaluation techniques
Explore NPL’s wide range of microwave and terahertz imaging techniques for NDE characterisation of materials.
Find out more about terahertz consultancy
Electrical sheet resistance, 2D conductivity and mobility
- Scope/range: Non-contact measurement of microwave sheet resistance/conductivity of thin films.
- Measured parameter: Perturbation of high-quality factor microwave dielectric resonator, measuring centre frequency and linewidth changes.
- Derived parameters: Sheet resistance, 2D conductivity, mobility.
- Suitability: Non-contact method. Thin films, buried conducting layers on relatively low-loss substrates.
Admittance methods
- Scope/range: 1 kHz to 10 MHz. Permittivity <10. Solids and liquids.
- Measured parameter: Impedance.
- Derived parameter: Complex permittivity.
- Suitability: Contact method. Solid specimens must be machined to size.
VNA coaxial probe/sensor methods
- Scope/range: 30 MHz to 50 GHz. Malleable solids and liquids.
- Measured parameter: Complex reflection coefficient.
- Derived parameter: Complex permittivity.
- Suitability: Contact. Malleable materials that do not require precise machining. Good for foodstuffs and polar liquids. Can be embedded in pipes with difficulty.
VNA transmission-line methods
- Scope/range: 100 MHz to 750 GHz. Permittivity <10. Solids, powders and grains.
- Measured parameter: Complex transmission and reflection coefficients.
- Derived parameter: Complex permittivity.
- Suitability: Usually contact method, but non-contact approaches are possible. Solid specimens must be machined to size. Gels, powders and grains can be measured.
Resonators
- Scope/range: 1 MHz to 144 GHz. Solids and powders.
- Measured parameters: Resonant frequency. Q-factor.
- Derived parameter: Complex permittivity.
- Suitability: Contact method. Solid specimens must be machined to size. Some techniques can measure piped liquids.
Terahertz time-domain spectroscopy – transmission
- Scope/range: 100 GHz to 5 THz. Solids, liquids and powders.
- Measured parameters: Transmission time and loss.
- Derived parameter: Complex permittivity.
- Suitability: Non-contact method. Solid specimens must be flat and plain-parallel. Liquids and powders must be contained in suitable cells. Can measure porosity.
Terahertz time-domain spectroscopy – reflection
- Scope/range: 100 GHz to 5 THz. Solids.
- Measured parameter: Reflectivity.
- Derived parameters: Spectral reflectivity. Real permittivity.
- Suitability: Non-contact method. Specimens must be flat.
Terahertz frequency-domain spectroscopy – transmission
- Scope/range: 50 GHz to 2 THz. Solids, liquids and powders.
- Measured parameter: Transmission loss.
- Derived parameter: Loss coefficient (approximate).
- Suitability: Non-contact method. Solid specimens must be flat and plain-parallel. Liquids and powders must be contained in suitable cells.
Terahertz time-domain spectroscopy imaging – transmission or reflection
- Scope/range: 100 GHz to 5 THz. Solids, liquids, powders.
- Measured parameters: Transmission time and loss.
- Derived parameter: Complex permittivity.
- Suitability: Non-contact method. Solid specimens must be flat and plain-parallel. Liquids and powders must be contained in suitable cells. Spatial resolution 1-2 mm.
Why choose NPL?
NPL is the UK's National Metrology Institute. It aims to promote advances in metrology that underpin non-destructive testing, condition monitoring and diagnostic engineering for design and quality assurance purposes. With state-of-the-art facilities and expertise in NDE, NPL is ideally placed to serve industry and academia by providing measurements and data analysis, consultancy and research to assist material assessment.
NDE consultancy and technical support
We're here to help. Still struggling to work out what you need? We pride ourselves on giving sound technical advice to guide you. By combining in-house expertise, standard tests and bespoke consultancy, you can be confident in our approach.
Condition monitoring
Learn how we enable early detection of Potential problems and reduce risk for industry
Contact us
Our research and measurement solutions support innovation and product development. We work with companies to deliver business advantage and commercial success.
Contact our Customer Services team on +44 20 8943 7070