Surecheck NDT

Visual Inspection nondestructive testing is one of the many ways we test the quality of welds at SureCheck. During a visual welding inspection, a weld is examined visually through the eyes to determine the quality of the weld and identify any discontinuities on the surface of the weld. Some common discontinuities that can be picked up during a visual inspection include surface cracking, undersized welds, overlap, undercut, either incomplete or excessive root penetration, excessive reinforcement, and burn-through.

Visual Welding Inspection is sometimes not associated with NDT, but it is the most widely used method of nondestructive weld testing within the fabrication & welding industry. Visual Welding Inspection activities will only find surface-breaking indications and welding profile imperfections.

All fabrication standards require visual inspection to be performed and various application standards would have varying levels of allowable imperfections to reach a visual inspection of welds standard.

Magnetic Particle Destructive Testing (known as MPI or MT) is sometimes specified in addition to the visual examination of welds. Magnetic Particle Inspection is used to find any imperfections that may not be immediately visible to the naked eye or where a small amount of assisted magnification is used.

How Does It Work?

For Magnetic Particle Inspection, the specimen is magnetized (either locally or in an overall capacity) either directly (when an electromagnetic current is passed through the material) or indirectly (when a magnetic field is applied from an outside source). If the integrity of the material is sound, the magnetic flux is predominantly contained within the material, however, if the surface of the material is flawed, local magnetic flux leakage appears surrounding the flaw. This leakage flux is displayed by applying very fine iron particles to the surface of the material, which when magnetized will accumulate around the area of flux leakage, which produces a build-up that can be seen by the eye even when the crack or imperfection in the weld is too small to be detected by a visual welding inspection. This allows for much smaller imperfections to be detected on the surface of the weld during an MPI inspection of welds.

These iron particles can either be used dry or, more commonly, suspended in a liquid known as magnetic ink. These are applied before and during the magnetization process, while the electric current is still flowing through the material, but sometimes residual magnetization is used, where the particles are applied after magnetization. Some forms of steel can hold magnetization for longer, which allows for smaller, more portable methods of MPI inspection of welds to be used.

Using a combination of two magnetic fields can produce a magnetic flux that swings and rotates, which can help detect a crack in any orientation of the material, which can be very helpful when carrying out a Magnetic Particle Inspection.

Limitations To Be Considered:

MPI inspection of welds is particularly sensitive to surface-breaking or near-surface imperfections such as 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 be magnetized 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.

An MPI test cannot however be used to detect deeply embedded flaws, nor can it be used on non-ferromagnetic materials, such as aluminum, copper, or austenitic stainless steel.

Magnetic Particle Inspection is also widely used on forgings, mechanical fixings such as bolts, castings, and other product forms that have a ferromagnetic capability.

Ultrasonic Tests (UT) are generally termed as a volumetric method of nondestructive testing. It is primarily used to find internal imperfections in welds or other product forms such as forgings, plate sections, etc. As one of the most common and popular nondestructive weld testing methods, UT weld inspection is primarily concerned with testing the thickness of a material to check for imperfections to the material such as erosion/corrosion and also laminations. The main principle of ultrasonic inspection is to transmit a sound wave into a structure, using the same transducer to pick up ultrasonic reflections of the original wave, which it then examines to create a picture of the structure and its thickness.

Ultrasonic inspection can sometimes be specified to ensure no laminations are present in materials that are to be subsequently welded in highly stressed joint configurations or, even after welding has taken place, to ensure imperfections such as lamellar tearing have not occurred during the welding operation.

How Does Ultrasonic Inspection Work?

During an ultrasonic test of welds, a strong specular reflection is required to resolve a flawed 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 manual ultrasonic inspection 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 behavior of the echo-dynamic pattern and shape of the flaw response (concerning 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 Ultrasonic Inspection find?

What gives ut weld inspection an advantage over weld testing methods is that it will detect 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 Ultrasonic Non Destructive Testing Used?

The ultrasonic method is used for the inspection of welds made in both ferritic and non-ferritic metals in pressure vessels, pipework, storage tanks, bridge structures, etc.

Our UT weld inspection services can be offered on or off-site to suit our customers’ needs.

Dye Penetrant Testing (known as DPI, PT, or Dye Pen) is sometimes specified in addition to the visual examination of welds. It is a type of testing where a dye penetrant can be used to carry out welding inspection and testing to find any imperfections that may not be immediately visible to the naked eye or where a small amount of assisted magnification is used. 

How Does PT Weld Inspection Work?

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

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

The time specified for the liquid 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 is 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 (colored) indications are broader than the actual flaw and are therefore more easily visible. Dye penetration testing can be performed in all positions and does not need to be in the gravity position.

There are several different liquid penetrant systems 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, As one of the top DPI testing companies in the UK, Surecheck can offer this method of nondestructive testing using a dye penetrant at our premises in Cannock.

The more 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. These methods can be offered on or off-site.

Important Considerations While Using a DPI Test

Despite DPI testing being one of the popular methods, liquid penetrant testing is often misused and spurious results can be obtained which are mainly down to operator error during PT weld inspection.

Some of the most common mistakes are: 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, anyone carrying out liquid penetrant inspections must be properly trained and qualified (for example, by the British Institute of Non-Destructive Testing’s PCN certification scheme or equivalent schemes such as those operated by CSWIP and ASNT) and work for reputable NDT companies in the UK.

At SureCheck, you can be confident in our diligent staff, high-quality equipment, and years of experience to conduct DPI testing efficiently. Get in touch for a quote or to find out more.