Physical Weld Testing Methods
Physical weld testing is not only essential for ensuring the strength and reliability of weld quality, but it is also a cornerstone of professional engineering projects. Many methods are available to test and assess welds, each with unique advantages and drawbacks. Many of these techniques rely on X-ray machines or visual inspections to detect cracks, pits, laps, sliver flaws and other blemishes in the material.
By understanding the appropriate physical welding inspection method for their needs, professionals can ensure the safety and longevity of their structures through careful examination and analysis. This knowledge can also be applied directly to industries such as aerospace engineering and materials handling specialists.
What Is the Difference Between Destructive Testing and Non-Destructive Testing
When engineers and material handling specialists need to determine a product's strength, performance, or reliability, Destructive Testing and Non-Destructive Testing offer two distinct evaluation strategies. Destructive Testing requires physical samples to conduct experimentations and tests to measure components breakage or disruption. Examples would include:
Non-Destructive Testing can be used when the risk of damaging the actual product is unacceptable. Instead of using destructive tests on real samples, these tests use non-invasive indicators such as ultrasound to measure and analyse sound waves, X-ray fluorescence to detect differences in composition within an object or magnetic fields that measure surface irregularities not visible.
Destructive Welding Tests
Destructive welding tests carry out a rigorous check to determine the quality of welds and other connections between metal parts. During these tests, engineers attempt to damage the welded connection to simulate the stresses and strains that might occur under real-world conditions. In addition, these tests can be tailored according to the specific application for which a joint is intended, mimicking impacts and conditions that would otherwise cause catastrophic breakdowns or even the destruction of welded components.
Acid Etch Test
Acid Etch tests involve exposing the material being tested to an acid that is capable of removing or etching away small amounts at a controlled rate, effectively providing insight into how metals react when exposed to chemically corrosive environments. These testing techniques give engineers and materials handling professionals valuable information needed to make informed decisions when selecting or designing components for any particular application.
Guided Bend Test
The guided bend test is a destructive welding test designed to evaluate the elasticity and flexibility of welded metallic structures. This test aims to determine if a particular weld will be capable of withstanding normal working conditions without deformation or cracking. To conduct the test, samples are subjected to a tension load applied perpendicularly and then bent using predetermined radius guides until failure. During the bending process, an inspector looks for any indication of cracking or discontinuities—if gaps appear between the specimen and guide blocks, it would indicate brittle behaviour in the welded joint.
Free Bend Test
This test works by taking a sample of the welded metal and stretching it until its breaking point. The shape and angle of deformation indicate the strengths and weaknesses of the material. Generally speaking, a specimen exhibiting lesser bending after fracture tells engineers that a better job was done in fabricating the joint. Areas on the sample that display deep fractures may point to potentially weak points or missed connections, while areas with minimal cracking suggest increased connective strength.
Back Bend Test
Destructive welding tests are essential diagnostic tools used to determine the efficacy of a weld. In particular, the Back Bend Test effectively measures the quality of fillet welds and lap joints. This test begins by cutting a large specimen from the weld of choice; technicians then carefully place each end in jigs on a tensile or bending testing machine.
The next step is to slowly subject the cut piece to a bending force which increases incrementally. Throughout this process, technicians use specific gauges to measure the distance between breakage points and any distortion in the specimen.
Nick Break Test
The Nick Break Test is used to evaluate the ductility of welded joints by measuring their resistance to tension. During the test, a single sample from the weld joint typically produced under actual working conditions is cut open at regular intervals along either side of the weld centerline.
These cuts create two separate tabs called 'nicks' that can be bent apart until they reach their breaking point. A low amount of nicks created due to too much material being removed will indicate brittle fracture failure, while too little material gone will lead to weak samples that might not pass validation tests.
Tensile Strength Test
This test examines the force it takes to deform or break a sample permanently. During this test, the sample weld is secured in a tensile testing rig and gradually subjected to increasing forces until it fails or reaches its peak stress point. Through careful analysis of the data collected during this process, engineers can determine whether a weld is up to code and learn essential details about the properties of the welded materials.
Non-destructive Welding Tests
Non-destructive Testing can detect even the smallest flaws that may otherwise be invisible until after the final assembly has been completed. However, this can cause costly issues down the line. Additionally, these tests often need to be carried out in rigorous and hazardous conditions, so specialised equipment is needed to protect operators against potential threats such as radiation or electric shocks.
Liquid Penetrant Testing
Liquid Penetrant Testing (LPT) is often used to examine offshore welds in oil and gas pipelines due to its ability to detect surface-level defects that can occur in otherwise invisible zones. During the process, a dye is applied to the part being tested, which is then rinsed off with a suitable solvent before being examined using ultraviolet or fluorescent light. The dye accumulates in tiny cracks or other discontinuities and presents as bright lines on inspection, allowing engineers to assess if any corrective action is needed.
Hydrostatic tests can identify the presence of leaks and defects in a material by pressurising it with a liquid. The pressure exerted is a result of two factors: the pressure of the pumping and the expansion of the fluid due to temperature changes. One benefit of this method is that it can be used on welds that are difficult to inspect visually because they are hidden or out of reach. In addition, it helps verify the integrity and strength of a welded structure, ensuring that it's safe for further use.
Magnetic Particle Testing
Magnetic particle testing (MPT) is a test that uses an electromagnetic field to detect flaws and cracks, even those located just beneath the surface. A liquid or dry powder containing iron particles is applied over the inspected area. If any cracking exists, it will cause the particles to be pulled away from their original location, creating visible indications on the surface. MPT is beneficial for detecting fatigue cracks, lack of fusion and internal discontinuities that cannot be seen with a visual inspection.
Eddy Current Testing
As a non-destructive test method, eddy current testing (ECT) is ideal for identifying defects in welded components. ECT uses alternative currents to generate electromagnetic fields within the tested material. These fields interact with the electrically-conductive pits and cracks in poorly welded areas, causing eddy currents that can be detected on the material's surface. With the correct equipment, ECT can detect even minor defects down to 0.05mm in depth, making it incredibly useful for quality assurance or welding inspection protocols.
Non-Destructive Welding Tests, such as Ultrasonic Testing, are a crucial part of quality control in welding operations. The test allows inspectors to verify that welds have been correctly made without damaging the components. During an Ultrasonic Test, high-frequency sound waves are sent through the sample material, and measurements are taken to determine its integrity.
There are many welding testing methods available to help you ensure that your welds are up to par. While some tests may be more expensive, they will all give you the information you need to know to ensure that your welds are strong and will hold up under pressure. Research and talk to a welding professional to decide which method suits you and your business.
Lenoch Engineering, as part of its capacity to provide precise engineering for the production, repair, and modification of vital componentry, offers coded welding. Our expert engineers are happy to assist you on various projects with a wide range of services. To learn more about our services, please do not hesitate to contact us.