Advantages and disadvantages of the test method and areas of application
Ultrasonic materials testing is an inspection technology that has been around since the Second World War, and can be used to perform a wide range of inspection tasks from raw materials to components to complex engineering structures, without damaging the structure in any way and without affecting its continued usability.
Ultrasonic material testing can detect deviations and defects in the structure of the material and can support industrial manufacturing processes at all stages: pre-production, production, maintenance and assembly.
A basic prerequisite for economical and safe operation is a correct assessment of the realistic condition and remaining lifetime of technical installations and structures. To achieve this, the use of non-destructive material testing processes is essential. Estimating the service life of equipment and structures and detecting deviations in time all contribute to safe and economical operation - for example, regular inspection and maintenance of aircraft and bridges can save lives, while correct estimation of the service life of oil tanks can avoid environmental pollution and huge financial losses.
The non-destructive material test is a diagnostic test to determine the current condition of the structure or equipment under test and to determine the extent of damage to the installed materials under the given operating conditions. During the operation of structures and equipment, damage is often caused by unexpected failures such as wear and tear or breakage, and timely detection of these can ensure safe and economical operation.
Description of the ultrasonic materials testing
The sound waves used in ultrasonic material testing are in the range from 500 Khz to 20 Mhz, which is inaudible to the human ear. Ultrasonic materials testing can be used on metals, ceramics, plastics and composites; however, it does not give meaningful results on paper and wooden components.
Ultrasonic testing uses the property of a high-frequency sound wave that travels at different speeds in different media. At the boundary of a material with a different acoustic density, the high-frequency sound beam is deflected or reflected - using this property of the sound wave, differences in the structure of the material can be filtered out, for example, to measure any inclusions or cracks in a weld or to measure the thickness of the material.
For a flawless part, the sound beam is reflected only from the boundary surface of the part, whereas if the part has a defect or misalignment, the defect location is an acoustic boundary surface from which part of the sound wave is reflected.
Ultrasonic materials testing requires an experienced materials tester, as there can be many influencing factors and false positives in the measurements - but with practice and experience these can be detected.
Factors affecting ultrasonic material testing can include: the microstructure of the workpiece, grain size, distance of the defect from the surface, defect shape, defect orientation and the difference in measurement impedances and waveform, so these influencing factors need to be taken into account for accurate test results. During material testing, spurious defects may also occur due to: failure of electrical parts of the measuring equipment, breakage of the transducer, air bubbles in the coupling medium, complexity of the workpiece shape, the effect of grain boundaries, variation of the waveform or the thermal effect zone of the weld. But an experienced material tester is prepared for these influencing factors and will even recommend additional non-destructive material testing to ensure accurate test results.
Ultrasonic material testing can identify any deviation or fracture in the part, showing the location, type and orientation of the irregularity. The reliability and accuracy of the inspection is increasing with the development of digital technology.
Advantages of ultrasonic materials testing
Ultrasonic materials testing has a number of Advantages van:
- because the penetration power of sound waves is high, this property allows the detection of defects and deviations even in thick materials.
- ultrasonic material analysis is very sensitive, allowing the detection of very small, flat defects and deviations that might not appear on a radiograph
- in many cases, it is sufficient to have access to the part under test from only one side
- higher accuracy of measurement than other non-destructive testing methods when determining the depth of structural defects
- high accuracy in determining the size, orientation, shape and type of the deviation
- non-radiative, so there is no harmful effect on nearby workers, no need for sealing, and the test can be carried out at the same time as the production process
- the instruments for ultrasonic materials testing are portable
- immediate results, so decisions can be made on the spot
Limiting factors for ultrasonic materials testing
Like all materials testing methods, ultrasonic materials testing has its limitations, disadvantages:
- complex geometric structure ultrasonic testing of structures can be cumbersome
- if you want to use an ultrasonic material testing method to measure the thickness is more expensive than using mechanical methods, and the acoustically diverse material composition can require multiple settings.
- this method of materials testing requires a skilled materials tester, as the composition of the material being tested, the structure of the component or the measuring device may influence the result or create a false error signal - these should be filtered out by the materials tester. Most of the time, if this is the case, additional non-destructive material testing methods must be used to obtain an accurate result
- parts that are not uniform in surface area, shape, size, thickness or homogeneity are difficult to ultrasonically inspect
- the surface of the component or structure must be thoroughly cleaned before this material testing technique can be used
- depending on the ultrasound test method, a coupling medium may be required to perform the test
- the component under test must be waterproof when using a water-based coupling medium, unless it is an anti-rust agent - the coupling medium is typically antifreeze
The tool and the professional
The most common application of the ultrasonic materials testing method is in welding seams examination. Ultrasonic materials testing allows the materials inspector to detect deviations in the weld and, by comparing them to a given standard, determine whether the weld is strong enough and can be used further or needs to be repaired.
The tests may vary depending on the size, type and environment of the welds - and of course the equipment used will vary accordingly. Material testers who test on-site with field service prefer instruments that are easily transportable, while those who test in hot manufacturing locations or on frozen pipelines prefer instruments with different specifications.
Each industrial sector has different test conditions and the type of instrumentation varies accordingly. Similarly, they vary from industry to industry the standardsthat must be met.
In addition, we have already touched on the fact that to accurately evaluate the results, you need a skilled materials examiner, who costs money and time to train. This is important because the materials inspector must be able to filter out factors that may influence the inspection and false defects; failure to do so may result in unnecessary repair work being required or the scrapping of the structure or component, which is an unacceptable loss. It is therefore important to choose the right specialist: it is advisable to work with a materials inspector who has experience in the industry and with the structure or component in question.
Non-destructive material testing technology is accepted and widely used, despite being a relatively expensive technology, because of the costs and losses saved by its use, measured in human lives, environmental pollution or simply in the downtime of production processes and the associated loss of revenue.
The air and space sector security investigations has added ultrasound to its range of tests. A carbon fibre aircraft and spacecraft parts, and structural components are particularly compatible with ultrasonic materials testing methods.
Another sector where ultrasonic materials testing is a commonly used testing method is the petrochemical industry, where oil can be used at every stage of the industrial process, from extraction and processing to transportation and storage. Detecting and correcting deviations and failures helps to avoid environmental pollution, accidents and material losses.
Ultrasonic material testing, although a relatively expensive non-destructive material testing technique, is essential to maintain safe and economical operation of engineering structures and facilities. Non-destructive material testing methods create the conditions for safe and economical manufacturing processes, from pre-production to maintenance.
Ultrasonic materials testing has a wide range of applications, few limiting factors and, in the hands of a good technician, reliable and accurate results.