Non-destructive Visual Testing (VT)

A visual inspection is one of the oldest, most reliable and most common methods for assessing the surface condition of a structure or material under test.

Visual inspection is the examination of the test substance with the naked eye. This type of inspection does not necessarily require special equipment, but it does require special knowledge so that the inspector knows what to look for when he or she inspects the object. 

During the visual inspection, the material inspector looks for deviations, defects or damage on the surface of the structure or material being inspected, which may be due to manufacturing, operation, transport or storage, and which differ from the expected quality.

visual inspection can occur on the raw material, at any stage of preparation, machining, on the finished product and at any time during operation.

The inspection test can be used to inspect castings, forgings, machined parts and welds in all industries.

The inspection can be stand-alone or complementary to other material testing procedures and can be used for damage analysis. From the point of view of access to the substance under test, visual inspection may be direct or indirect. In the former case, the use of a magnifying glass, microscope or projector is allowed, in the latter case the examiner does not see the test material directly with his own eyes, but examines it on the basis of a photograph, video or some other aid between his eyes and the object. These may include mirrors, endoscopes, fibre optic equipment and, more recently, drone video systems, which are part of remote or remotely operated material testing, as discussed later.

During the visual inspection, the material inspector is mostly looking for cracks, deformation, corrosion, discolouration, physical damage to the material, and surface cracks, craters, and defects and other abnormalities visible to the naked eye on the welds.

The relevant standard (MSZ EN 13018) does not require the materials tester to be VT-certified, but the tester must be familiar with the relevant standards, the product, the manufacturing process and the auxiliary equipment. Calibration of auxiliary equipment should only be carried out by a materials tester with a minimum level 1. As it is perhaps the most subjective of all materials testing methods, qualitative visual inspection requires a great deal of experience.

The inspection by eye is used in all industries, as inspecting a structure or material with the naked eye is one of the easiest ways to find deviations or defects. The primary purpose of detecting deviations by visual inspection is to ensure that they are corrected if they can be corrected, but in many cases it can also prevent the unnecessary use of a more expensive materials testing procedure.

Advantages of on-site visual inspection:
- The least expensive materials testing method
- Minimal or no equipment required
- Requires minimal materials preparation

Disadvantages of in-site visual inspection:
- Only suitable for detecting surface deviations
- Only relatively large deviations can be detected
- Highly subjective method: risk of misinterpretation of defects

Remote or remotely controlled materials testing

The continuous and very rapid development of information technology (IT), nano- and microelectronics, robotics and digital imaging is also having a major impact on materials testing technologies. Material testing techniques that allow the remote control of the material tester's device to study the product or structure under test from a considerable distance already exist and are likely to become widespread soon. It is likely that in the future, the inspection will increasingly be carried out by an operator and a robot, with the expert evaluating the deviations being located anywhere in the world.

Remote Visual Inspection (RVI)

As indicated at the beginning of this article, visual inspection is not always necessary or possible in person.

Thanks to the continuous development of imaging technology and robotics, materials scientists are increasingly using RVI tools to collect visual data instead of face-to-face. RVI drones are equipped with special sensors, civilian or other industry drones are not suitable for materials testing.

Remotely guided inspection is most needed when the structure to be inspected is in a difficult-to-access location or the work area is hazardous, or both.

For example, entering a mine after an explosion is life-threatening. A drone can be used to remotely assess the area visually, allowing management to decide what action to take until the immediate danger is averted.

To take a less extreme example, the inspection of a huge oil storage tank can be potentially dangerous because it requires scaffolding tens of metres high. The drone can be used to rule out an accident, while allowing the inspector to take a visual inspection - using its high-resolution camera, which is more powerful than the human eye and can take as many shots as he or she wants.

This is considered an indirect visual inspection, but advances in technology allow for a more in-depth examination than the earlier and direct method.

Of course, it is not only drones that can be used for remote visual inspections; experiments have been carried out in the past with cameras attached to ropes to reach the inspection site, or with cameras attached to robots. Drone technology is successful because it offers very sensitive and accurate guidance and high quality imaging.

The benefits of drone technology:

Drones improve safety by eliminating the need for the inspector to enter or climb into confined or dangerous spaces.

Cost savings
Investigating in high or dangerous places often requires costly scaffolding and longer shutdowns. Drone technology requires no scaffolding and significantly reduces the time required for inspection, resulting in significant cost savings.

High-quality data
The new inspection drones collect high-quality visual data that can be archived.