To get the best result during testing, you need the best tools with accuracy and good accessibility to the area required for testing.
In welding, X-ray weld inspection and ultrasonic testing are two of the most popular inspection and testing methods used to ascertain weld quality.
The reason is that they are both non-destructive methods which means test samples can still be used as products after testing, and they offer some of the best advantages for welding inspection.
However, they are not without their limitations, making their applications specific to certain welding inspections, hence their restrictions.
Let’s have a look at these two weld inspection techniques in detail, as well as their differences.
What is x-ray weld inspection?
X-Ray Weld Inspection is a non-destructive method of weld inspection.
This type of inspection is among the most used as a material quality control tool, and is frequently used in several Petrochemical, Chemical, Steel, Naval, Pulp and Paper, Aerospace, and many other industries.
The X-Ray welding inspection function provides information on the defect content of a specific product and the technological characteristics of a material. Furthermore, it is also used to monitor the degradation of components, equipment, and structures.
The X-Ray weld inspection is highly efficient because, during its execution, a non-invasive technique is used to analyze the material or equipment without causing them any damage.
This way, producers can do it during the manufacturing, construction, assembly, or maintenance steps. In addition, it is a low-cost service and economically interesting for companies.
The equipment used in the X-ray Welding Inspection must be calibrated with total precision and undergo periodic maintenance.
This precaution ensures that the analysis of the material will be correct and will not show future inconsistencies. It is also necessary to follow specific test execution procedures, strictly following the required technical criteria and standards.
What is Ultrasonic Testing in welds?
Ultrasonic inspection in welds is based on the phenomenon of reflection of acoustic waves when they encounter obstacles to their propagation inside the material.
The wave will be reflected and will return to its generating source if the obstacle is in a normal position (perpendicular) concerning the emitted sonic beam.
Ultrasonic testing is a widely used non-destructive testing method worldwide for checking internal discontinuities in welded materials.
Generally, users can estimate the actual dimensions of an internal discontinuity with reasonable accuracy from the height of the reflected echoes. This method provides a means for the part to be accepted or rejected based on the acceptance criteria of the applicable standard.
The most significant applications of this test are related to the inspection of castings, forgings, rolled parts, boilers, and thickness measurement.
These applications are in addition to the detection and depth measurement of cracks related to the preventive inspection of components in use.
Another great use is its use to inspect welds of steam pipes carried out in the field as a replacement for X-ray weld inspection and testing. The idea is to avoid the need to evacuate the work area to protect against x-ray emissions.
Its application is essential, for example, in the detection of cracks in milling shafts when mounted on sleeves that operators will not draw during stops. With this technique, it is possible to sweep the region of the shaft inaccessible due to the assembled liner to check the presence of cracks in this area.
What’s the difference between them?
While X-ray weld inspection has had a long-running competition with other non-destructive testing methods like the Ultrasonic testing method, it still offers significant advantages over other techniques.
One of these advantages is its precise imaging technology which simplifies the analysis of welding defects. Its digital imaging feature has replaced film usage, particularly for pipe end inspection, reducing the time required for weld inspection.
The accuracy of the X-ray weld inspection is also very high relative to ultrasonic weld inspection, either for full weld inspection or spot-checks.
Documenting weld inspection results for instant and future references is another difference that sets X-ray weld inspection apart. It has the tools to record weld images while in motion.
On the other hand, the ultrasonic weld testing method poses some limitations, such as its unsuitability for parts manufactured with materials with high acoustic attenuation. These materials include gray cast iron, non-ferrous metals (like bronze), and steels with coarse microstructure (without heat treatment).
Parts of complex geometry make it challenging to carry out ultrasonic weld tests, as the technique requires that the region to be swept has parallel surfaces. High temperatures also make its application difficult.
Ultrasonic testing also requires a lot of theoretical knowledge and experience on the part of the inspector and surface preparation.
Also, the permanent record of the test is not easily obtained as very narrow ranges constitute difficulty in applying the method.
Calibration is another critical consideration when using ultrasonic testing as a standard block is required, which must be made of a material that is acoustically similar to the part to be tested. This standard block will also include calibrated reference thicknesses and holes. If the device’s calibration were made in block and part of dissimilar materials, the measurement accuracy would be affected.
In some cases of weld inspection, there is a need for the total removal of the weld reinforcement, which often takes up the production time.
Ultrasonic testing of materials with surface waves is applied with severe restrictions, as only surface defects are observed. This application is where X-ray weld inspection is of great benefit as it can detect this type of discontinuity.
Finally, you need to be aware of the principles employed in both the X-ray weld inspection and the ultrasonic testing of welds.
The summary of the limitations of these non-destructive testing methods for welding, as explained above, is the inability of ultrasonic testing to tackle non-surface welds. In contrast, the X-ray method can check internal weld defects such as discontinuities.
This knowledge will help you assess their best applications as well as their limitations. It will also help you decide the best suitable testing method for your welding inspections and quality assessment.