Modern Videoscope Capabilities for Easier Weld Inspection
Nondestructive examination plays an important role in equipment diagnosis during the maintenance of welded structures. However, inspection using ultrasonic flaw detection can be difficult or even impossible if the weld is inaccessible. The good news ...
Nondestructive examination plays an important role in equipment diagnosis during the maintenance of welded structures. However, inspection using ultrasonic flaw detection can be difficult or even impossible if the weld is inaccessible. The good news is that new remote visual inspection (RVI) technologies have been developed that enable highly efficient and accurate weld inspection. Testing methods are also diversifying.
Lead photo: Videoscope inspection of a weld inside a pipe.
One RVI technology that offers more effective weld inspection is the modern industrial videoscope, an advanced type of borescope with video and still image recording capabilities. This article will review the videoscope’s capabilities for overcoming common weld inspection challenges.
The Challenges of Visual Inspection in Welding
The ISO standard for visual inspection of welds in metallic materials (ISO 17637:2016, Non-destructive testing of welds — Visual testing of fusion-welded joints) states that welds can be inspected directly if access is sufficient or remote using borescopes and other relevant RVI equipment.
An industrial videoscope can be inserted into pipes and tanks that cannot be accessed from the outside, giving inspectors a clear view of the welded parts inside. This visual inspection helps inspectors determine the need to repair or replace equipment for pipes and tanks.
Many modern videoscopes come with a measurement function that can quantitatively measure the length, height, depth, and sizes of defects. Even if it is hard to judge the need for repair from the image of the weld, the measurement function can aid in the visual inspection. This function also eliminates the need for extra equipment like gauges to take measurements.
Conventional 2D images have generally been used for videoscope measurements of cracks, heat effects, and corrosion on welded parts. Yet, these 2D images present a challenge: It is hard to visually determine depth on a flat image. Since the inspector must place the measurement points manually, it takes time to confirm the measurement and can lead to reduced confidence in the results.
Improving Videoscope Measurement Efficiency with 3D Modeling
Some videoscope models have a measurement function with 3D modeling, which provides a more efficient measuring solution than using only 2D images (Figure 1).
Figure 1: 3D modeling makes for more confident depth measurements.
Simply put, 3D modeling is a videoscope feature that helps inspectors easily understand the shape of complex components through various 3D displays of the target object. For example, you can rotate the 3D model of the target to check the positions of the measurement and reference points, remove unnecessary objects from the cross-section display, and color code the protrusions and dents to see them at a glance (Figure 2).
Figure 2 — Color-coded visuals enable fast analysis of protrusions and depressions.
With 3D modeling, the target’s surface shape can be shown three-dimensionally, helping inspectors understand the uneven surface area. By rotating the 3D model, the inspector can easily and quickly determine where to place the measurement point. Another benefit is that the deepest and highest points are automatically displayed. This eliminates the need to manually search for the measurement points, saving time and enabling accurate measurements.
By understanding the shape of the welded part with 3D modeling, inspectors can quickly measure its width, height, and pitch (ratio of width and height). 3D modeling is particularly helpful when measuring the height of a welded part in the inner wall of a thin pipe since it is necessary to set a reference plane for this task. By optimally arranging the reference plane’s width on the pipe’s curved surface while looking at the 3D model, the inspector can accurately and quickly measure the weld dimensions.
When measuring a welded part’s height at the inner diameter (ID) of the pipe (pipe ID), the depth is measured by comparing it with the reference plane set by the inspector. However, it is difficult to create a reference plane wide enough to lay flat on the curve of the pipe ID. 3D models are useful for this task. The inspector can rotate the 3D model to see the reference plane’s location and how close it is to the curve. This important information cannot be obtained from 2D images.
Other Technologies for Remote Visual Inspection of Welds
Welding inspections are often performed inside large-diameter pipes, tanks, and vessels as well as on the dark inner walls of pipes. Yet, many videoscopes lack enough illumination for these large or dark spaces, making it difficult to find the welded part that must be inspected in detail. The inspector must repeatedly approach the wall and scan a specific area to find defects — a time-consuming method that can cause defects to be overlooked in the dark.
Proper illumination is also important for 3D modeling, since the target must be illuminated with enough light to acquire the measurement data needed to generate a 3D model. One solution to achieve more illumination is to use a modern industrial videoscope with a laser diode light source.
When a laser diode light source comes from the videoscope’s main unit and uses optical fiber to transmit the light to the tip of the insertion tube, it generates a bright, focused light to illuminate the target. Inspectors can see their target clearly in dark spaces using the latest laser diode illumination systems.
In addition to proper illumination, it is important to suppress reflected light from metal materials to perform accurate observation and acquire measurement data. The latest image processing technologies can adjust the amount of light and improve the image quality based on the target to solve this challenge.
With these modern videoscope technologies, inspectors can generate a sufficient 3D model even in a challenging environment for visual inspection. The result is faster weld measurements and more confident inspections.
A modern industrial videoscope equipped with 3D modeling, laser diode illumination, and image processing technology is an effective solution to inspect pipe welds. Measuring weld dimensions in narrow or large spaces, such as a large-diameter pipe or tank vessel, can be performed accurately and in a shorter time than with a conventional 2D measurement image.
As a result, inspectors can accurately and quickly determine the need for repair.
This article was written by Masateru Ito (marketing specialist, remote visual inspection, at Olympus Scientific Solutions, Waltham, Mass.) for the American Welding Society.