Welding is a method of joining metal components using hot metal, either from a third piece that is being applied hot, or heating areas of the metal components to be joined until they fuse. This fabrication method is commonly applied for producing parts that will be functioning under relatively high mechanical stress, and therefore need a stronger bond than other metal joiners like rivets can provide. Because of the intensity of mechanical duress that a welded component may experience, welding inspections are an important way to ensure quality and consistency in the manufactured parts- as well as safety during their eventual use.
A weld can be evaluated by several criteria. The first is size. Even if a weld is executed correctly in terms of being without flaws, the choice of weld size can be a danger if it is not suited to the intended application the component will be used for. Larger, thicker welds have a tangible effect on the strength of the part, as well as where an eventual failure would occur. The second criterion is defect rate. Once the size of the weld is determined to be suitable, it must be executed correctly. It should be inspected for any discontinuities or flaws, as these can lead to stress concentrations during mechanical service which can ultimately cause the part to fail at lower than its rated specifications.
There are several methods that can be employed by a weld inspector, and they exist on a continuum of aiming to minimize cost and aiming to detect even minute problems. A visual inspection is the most cost effective method because of how quickly it can be performed and without specialized equipment- however, there are trade-offs in thoroughness as this method can only catch weld defects that are large enough to be visible to the eye and show up on the surface of the weld. Evaluating the size of the weld is done very effectively via this method. A second method is surface crack detection, which can, as the name suggest, locate even very minute cracks. This can be a good option for parts that are intended for very mechanically rigorous applications, especially those where they will be exposed to vibration or corrosion. A third method is radiographic and ultrasonic weld inspection. This is high on the cost scale due to the specialized equipment needed, but it’s a very thorough method at detecting both small defects and defects that may be buried beneath the surface of a weld. Finally, there is destructive weld testing which involves destroying the component to search for imperfections. While this is incredibly effective at detecting how a part may fail, it’s obviously not possible to test all manufactured components in this way since they are not usable after testing. A limitation therefore is that “representative” articles must be selected, and this may not catch all defects.
Welding is a widely-used fabrication tactic, but not all welds are created equal. Ensure the quality of your components by employing one of the methods of weld testing.