When NDT (Non-Destructive Testing) procedures don’t measure up, then weld inspectors opt for destructive weld testing methods. As the label implies, small samples of the subject weld are exposed to destructive energies. That’s not a task that can be addressed with a carefree demeanour. Unlike a radiographic test, this procedure affects weld zones, so these techniques must be utilized with caution. We’ll begin by looking at acid testing methods.
Destructive Weld Testing: Acid Etch Examinations
If present, concealed weld discontinuities come to light when an acid reacts with a fused material. When a sample is removed from a weld, it’s polished and cut into cross-sections. The acid, often formulated as a mild hydrochloric or nitric acid solution, then breaks down any concealing materials and reveals the clean edges of each sectioned area. Porosity issues are often discovered by adopting this technique. Transition sites, between base metals and weld materials, are also made clearer by acid etching.
Guided Bend Weld Tests
Mounted on a jig and die assembly, the welded metal is forcefully bent. The bending action continues until the specimen reaches the desired angle, for this means the weld area has assumed a predetermined bend radius. To be clear, this approach looks closely at the ductility and strength of a selected welding process. By using face bend tests, transverse bends, and other force-directed flexing actions, the inspection can also uncover liner fusing defects. If the ductility test does fail, weld cracks will appear.
Tensile Strength Tests
Pushing the weld beyond its material limitations, this is often the only way to determine the tensile properties of a fusion joint. A large piece of equipment applies massive amounts of mechanical energy to the specimen. It rips apart transversely or breaks at a critically weakened juncture. Used in conjunction with an acid etching test, failure analysis science delves down into the flaw to discover the cause of the discontinuity. This test usually involves sending the part to a stationary hydraulic press, although there are portable variants, machines that come equipped with movable crushing jaws and hydraulic power.
As stated several times during this post, the welds tested here are mostly specimens. They’ve been created to test a welder’s skills, to see how a technique will serve a new project, or for some other intelligently mandated reason. There are nicks and indentations to make, cross-sections to cut, and acids to carefully apply here, so the NDT approach isn’t applicable. In place of that approach, these “specimens” will be broken and tortured in every imaginable way, all the better to establish the skills of a welder or the limitations placed upon a new engineering project.