Non Destructive Testing Inspections for all sectors of the welding, fabrication and engineering industry under our ISO 9001 system


Non Destructive Testing for the Welding Industry

WQ Inspection & Certification offer a range of high quality, cost effective NDT Inspections to various industry sectors across the UK.

With over 20 years experience in Non Destructive Testing, our skilled personnel offer a high degree of expertise and product knowledge. Our customer focused organisation means we offer a reliable and rapid response to meet your requirements.

We can currently offer a mobile Non Destructive Testing inspection service and can cover various NDT disciplines including; Ultrasonics, Dye Penetrant, Magnetic Particle and Visual Inspection.

Our operators are certified in accordance with BS EN ISO 9712 using the popular PCN Scheme.


Non Destructive Testing Services available

  • Ultrasonic weld inspection
  • Portable DPI and MPI techniques
  • Ultrasonic thickness checking surveys
  • Radiographic interpretation
  • Through thickness lamination checks
  • Pre and In-service inspections
  • Procedure writing and reviews

Dye Penetrant Inspection

What is it?

Liquid (or Dye) penetrant inspection (DPI) is an extension of visual inspection and is used for detecting surface-breaking flaws, such as cracks, laps and folds, on any non-absorbent material’s surface.

Find out more about DPI

How does it work?

Firstly, the surface to be inspected is cleaned thoroughly to remove all traces of dirt and grease.

A brightly coloured or fluorescent liquid is then applied liberally to the component surface and allowed to penetrate any surface-breaking cracks or cavities.

The time the liquid is allowed to soak into the material’s surface is normally about 20 minutes. After soaking, the excess liquid penetrant is wiped from the surface and a developer applied.

The developer is usually a dry white powder, which draws penetrant out of any cracks by reverse capillary action to produce indications on the surface. These (coloured) indications are broader than the actual flaw and are therefore more easily visible.

A number of different liquid penetrant systems are used in industry. Fluorescent penetrants are normally used when the maximum flaw sensitivity is required. However, these penetrants must be viewed under darkened conditions with a UV lamp, which may not be practical.

The most commonly used systems are solvent removable, or water washable, red dye systems, which typically comprise three aerosol cans – cleaning fluid, penetrant and developer. These systems are often used to check weld quality during fabrication.

Important considerations

Despite being one of the popular Non Destructive Testing methods, liquid penetrant testing is often misused. Test surfaces are not cleaned adequately, the contact time between the penetrant and the test surface is too short, or the excess penetrant is removed carelessly (i.e. from flaws as well as from the test surface). For these reasons, it is important that personnel carrying out liquid penetrant inspection are properly trained and qualified (for example, in accordance with the British Institute of Non Destructive Testing’s PCN certification scheme or equivalent schemes such as those operated by CSWIP and ASNT).

Non Destructive Testing - Dye Penetrant Inspection

Magnetic Particle Inspection

What is it?

Magnetic particle inspection (MPI) is a Non Destructive Testing method used for the detection of surface and near-surface flaws in ferromagnetic materials.

Find out more about MPI

How does it work?

A magnetic field is applied to the specimen, either locally or overall, using a permanent magnet, electromagnet, flexible cables or hand-held prods. If the material is sound, most of the magnetic flux is concentrated below the material’s surface. However, if a flaw is present, such that it interacts with the magnetic field, the flux is distorted locally and ‘leaks’ from the surface of the specimen in the region of the flaw.

Fine magnetic particles, applied to the surface of the specimen, are attracted to the area of flux leakage, creating a visible indication of the flaw. The materials commonly used for this purpose are black iron particles and red or yellow iron oxides. In some cases, the iron particles are coated with a fluorescent material enabling them to be viewed under a UV lamp in darkened conditions.

Magnetic particles are usually applied as a suspension in water or paraffin. This enables the particles to flow over the surface and to migrate to any flaws. On hot surfaces, or where contamination is a concern, dry powders may be used as an alternative to wet inks. On dark surfaces, a thin layer of white paint is usually applied, to increase the contrast between the background and the black magnetic particles. The most sensitive technique, however, is to use fluorescent particles viewed under UV (black) light.

In some cases, MPI can leave residual fields which subsequently interfere with welding repairs. These can be removed by slowly wiping the surface with an energised AC yoke.

What will it find?

MPI is particularly sensitive to surface-breaking or near-surface cracks, even if the crack opening is very narrow. However, if the crack runs parallel to the magnetic field, there is little disturbance to the magnetic field and it is unlikely that the crack will be detected. For this reason it is recommended that the inspection surface is magnetised in two directions at 90° to each other. Alternatively, techniques using swinging or rotating magnetic fields can be used to ensure that all orientations of crack are detectable. It cannot, however, be used to detect deeply embedded flaws, nor can it be used on non-ferromagnetic materials, such as aluminium, copper or austenitic stainless steel.

Non Destructive Testing - Magnetic Particle Inspection

Ultrasonic Weld Inspection

What is it?

Ultrasonic Testing (UT) is a Non Destructive Testing method used for the detection of surface and sub-surface defects and flaws.

Find out more about UT

How does it work?

A strong specular reflection is required to resolve a flaw response from the background noise level with pulse echo ultrasonics. For planar flaws (cracks, lack of fusion, etc.) a specular reflection will only result if the ultrasonic beam is normal (or near normal) to the plane of the flaw. Angled beam shear wave probes are commonly used for the manual ultrasonic inspection of welds in ferritic steels, as these provide the only way of directing ultrasound into the weld body when the cap reinforcement is still present. Where a weld cap restricts probe movement, the sound can be reflected off the bottom surface and directed into the weld body under the cap.

Where sound is angled directly at the area of interest, this is referred to as “half skip testing”. “Full skip” testing occurs when the bottom surface is used to reflect the sound before it enters the weld.

For a typical girth weld, a 45° probe is used for inspecting the root region, and 60°/70° probes for the sidewall fusion faces and weld body. The behaviour of the echo-dynamic pattern and shape of the flaw response (with respect to probe movement) can be used to identify the type of flaw, estimate the length and, in some cases, the through-wall height of the flaw.

What will it find?

Most manufacturing flaws (lack of sidewall fusion, lack of root fusion, lack of root penetration, porosity, solidification cracking, etc.) and in-service flaws (fatigue cracking, stress corrosion cracking, etc.).

Where is it used?

Inspection of welds made in both ferritic and non-ferritic metals in pressure vessels, pipework, storage tanks, bridge structures etc.

Non Destructive Testing - Ultrasonic Inspection