A Brief Overview of Welding Inspection
A good weld quality is characterised by a smooth, consistent, and uniform appearance. Typically, the process of weld inspection involves a series of quality control initiatives conducted by welding inspectors. The primary objective of these inspections is to ensure that the welded joints are able to meet the required quality criteria. Depending on factors such as material type/thickness, specific defects of interest, and joint configuration, many welding inspection techniques are applied.
During welding inspection, it is possible to evaluate many different characteristics of a weld. Some of these characteristics relate to weld size, and others are related to the presence of discontinuities in the weld. The size of a weld is extremely critical because it has a direct impact on the strength and performance of a weld. If the weld is undersized, it may not be able to withstand the applied stress during service.
Weld discontinuities, on the other hand, are imperfections within the weld or adjacent to it. Weld discontinuities may or may not depend on the weld size and/or weld location. In presence of these discontinuities, the weld is unlikely to meet its intended level of performance. In the worst case scenario, this type of imperfection can reduce the weld strength to cause premature weld failure.
There are many reasons for inspecting welds, the most fundamental of which is to determine the suitability of the weld for its intended application. The first step for the evaluation of weld quality is to have a measuring block for the comparison of weld characteristics. Without a specified acceptance criteria would be impractical.
There are a number of sources for originating weld quality acceptance criteria. Weld sizes and other dimensional information such as weld location and length can be obtained from the welding fabrication blueprint. The levels of acceptable and unacceptable weld discontinuities for inspection purpose are available from the welding standards and codes. Welding inspectors also play a vital role in this process. They must have a thorough understanding of welding procedures, drawings, symbols, code and standard requirements, joint design, and inspection and testing techniques. This is why it is extremely important for the welding inspectors to have adequate qualification as well as experience.
Discussed below are some of the most important areas of welding inspection.
- Visual inspection: This is the easiest and the least expensive of all welding inspection techniques. However, for many applications, this is a highly effective inspection method, if the process is carried out properly.
- Surface Crack Detection: Liquid Penetrant Testing (PT) is the most common method for the detection of weld surface cracks. Colour Contrast and Fluorescent Dye are the most preferred testing methodologies with this testing category. For ferromagnetic materials, Magnetic Particle Testing (MT) can also help detect discontinuities such as porosity, cracks, inclusions, seams, lack of fusion, etc.
- Radiographic and Ultrasonic Inspection: This Non Destructive Testing (NDT) method is used for the examination of internal weld structure to establish its integrity without causing any damage to the weld component.
- Destructive Testing: In this method, weld integrity is established by breaking the welded component so that its physical and mechanical characteristics can be evaluated.
If you have more questions related to weld quality inspection and testing, please contact us at Coating Management solutions.