What this category covers
Non-destructive testing verifies the integrity of a component without destroying it, which is what makes it the standard tool for weld inspection, castings, forgings, pressure vessels and in-service piping. Because the part survives the test, it can be inspected again later, and a survey repeated over years shows whether a wall is thinning rather than merely whether it is thin today.
The five principal methods detect different defects and are frequently used in combination rather than as alternatives. Surface-breaking defects answer to penetrant or magnetic particle inspection, near-surface cracks in conductive material to eddy current, volumetric defects and wall thickness to ultrasonic or radiographic inspection. Choosing between them is a question of defect type, material and access, and it is usually settled by the acceptance standard rather than by preference.
Buyers search for this discipline by method and by standard, not by product family, which is why it stands as its own top-level category rather than sitting inside general inspection equipment. The method also brings its own peripheral scope - probes, coils, reference blocks, couplant, film and the certification of the operator - and a set that ignores those items does not complete an inspection.
Product types in non-destructive testing equipment
| Product type | How it works | Usually specified for |
| Ultrasonic flaw detector | High-frequency sound transmitted into the material, with echoes returned from the back wall or from a discontinuity | Weld and forging inspection and internal defect detection in metals, where a single-sided access is all that is available |
| Ultrasonic thickness gauge | Time of flight to the back-wall echo, converted with the sound velocity of the material | Wall-thickness surveys on pipe, tanks and pressure vessels, and corrosion monitoring repeated over a period |
| Eddy current tester | Circulating currents induced in conductive material, with the coil sensing changes in conductivity or geometry | Surface and near-surface cracks in tube, bar and weld, and heat-exchanger tube inspection where the inside has to be reached |
| Magnetic particle inspection equipment | Magnetisation of a ferromagnetic part, with the defect revealed by particles attracted to the leakage field | Surface and near-surface cracks in steel welds, castings and forgings, where fast coverage of an area is wanted |
| Dye penetrant inspection equipment | A penetrant drawn into a surface-opening defect and then developed to make it visible | Non-magnetic materials - austenitic stainless steel, aluminium and ceramics - where magnetic methods do not apply |
| X-ray inspection equipment | Penetrating radiation recorded on film or on a digital detector | Internal defects, castings, weld quality and assembled parts, where a permanent image is required |
| Industrial radiography equipment | An isotope source or a tube, together with the handling, collimation and shielding around it | Field radiography of weld and pipe, where access and radiation safety have to be planned as part of the job |
| NDT reference blocks and accessories | Reference reflectors, couplant, probes, coils, films and markers used to set up and verify the methods above | Calibration and setup against a defined standard, and the consumables that complete an inspection set |
Probes, coils, couplants, films, markers and scanners are listed under this category as well, and are frequently the items that decide whether an inspection can actually be carried out.
How to choose a non-destructive testing instrument
There is rarely a single correct instrument for a duty, but there is always a
shortlist that can be justified and a set of answers that eliminates the rest. These
are the questions that decide it.
- The defect type and where it sits - surface, near-surface or volumetric. This is the first question, because it separates the methods before any instrument is discussed.
- The material and its properties: conductivity, permeability and grain structure decide whether eddy current, magnetic particle or ultrasonic inspection is applicable at all.
- The acceptance standard and the acceptance level within it, since the standard defines the method, the coverage and the record that has to be produced.
- Geometry and access: thickness, curvature, diameter, and whether both sides of the joint can be reached.
- Surface condition and preparation, because coatings, scale, roughness and paint affect each method differently and change how long the inspection takes.
- Coverage and speed: a spot check, a full weld scan and a survey across a large area are three different equipment specifications.
- Whether a record has to be kept, and in what form - readings logged over time, a radiograph on film, or a written report signed by a certified operator.
- Operator certification and the equipment documentation the end customer expects, which is often a contractual requirement rather than a technical one.
- Where the inspection takes place - workshop, field or confined space - since that decides portability, power and the handling equipment that has to travel with the set.
Working through the selection in order
- Start from the acceptance standard and the defect types it requires you to look for, rather than from a preferred method.
- Establish whether the defect is expected at the surface, just beneath it, or inside the material.
- Check the material against the method: ferromagnetic for magnetic particle, conductive for eddy current, any non-porous material for penetrant.
- Confirm access - both sides for radiography, a couplant path for ultrasonic, a clean surface for penetrant - before going further.
- Decide the coverage and the speed required, and whether the inspection is a one-off or a survey repeated on a schedule.
- Fix what has to be recorded and in which form, including any requirement for an image or a signed report.
- Choose the probe, coil, source or consumable that matches the geometry, since the accessory is often the item that decides feasibility.
- Confirm the certification route for the operator and the documentation for the equipment, then price the complete set rather than the instrument alone.
Comparing the technologies
| Method | Best suited to | Limits | Detects |
| Ultrasonic testing | Volumetric defects in metal, thick sections, and wall-thickness measurement | Needs couplant and an operator who can interpret the trace; geometry, coatings and coarse grain structure scatter the beam | Internal discontinuities, wall loss |
| Eddy current testing | Surface and near-surface defects in conductive material, and tube inspection from the inside | Limited to conductive material and to a shallow depth; the probe has to suit the geometry | Cracks, conductivity variation, corrosion |
| Magnetic particle testing | Ferromagnetic parts, with fast coverage of a weld or a casting surface | Applies to ferromagnetic material only, and the part must be magnetised in the direction that reveals the defect | Surface and near-surface cracks |
| Dye penetrant testing | Any non-porous material, including austenitic stainless, aluminium and ceramics | Surface-breaking defects only, and the cleaning and surface condition decide whether the result means anything | Surface-breaking defects |
| Radiographic testing | Internal defects and assembled parts, where a permanent image is part of the deliverable | Needs access from both sides and radiation safety controls, plus a source or tube with the associated handling | Volumetric defects, weld quality |
| Wall-thickness gauging | Corrosion surveys repeated over time to show a trend rather than a single value | Needs the sound velocity for the material and a prepared surface; coatings and curvature affect the reading | Remaining wall thickness |
Parameters to confirm before ordering
What is left after the technology is chosen is a list of values that only the
installation can supply. These are the ones that change the model, the price or the
lead time:
- The method or methods required, and the acceptance standard with the level to be applied.
- The defect types being looked for, and where in the material they are expected to occur.
- The material, its thickness, and its conductivity or permeability where that is relevant to the method.
- The part or assembly: geometry, dimensions, curvature and surface condition.
- Access: whether both sides can be reached, and whether the inspection is in a workshop or in the field.
- The coverage required and the inspection rate, if a schedule or a shutdown window has to be met.
- The record required - readings logged, images stored, or a written report - and in what format.
- Certification: the level the operator is expected to hold, and any equipment documentation the customer specification names.
- Power and conditions at the inspection point, including confined-space access and radiation-safety constraints.
- Accessories and consumables needed with the set: probes, coils, reference blocks, couplant, film, markers or scanners.
Figures are quoted, not assumed
Specifications vary by model and application, so no performance figure is stated on
this page. Where a parameter has not been documented for a particular model, the
product page says so rather than filling the gap with a plausible number. Send the
values above and we will return the ones the selected model actually holds.
Where these instruments are used
