Posted in Special Measuring Systems.
Characterization of surface defects in tubes and pipes
Regardless of the production process, the management of surface defects in tubes and pipes is one of the areas of main interest in the production process. A surface crack or a hole can be the origin of a crack or a corrosion process when the element is in service. Non-destructive testing is the best method for both detecting and characterizing defects. Once the defect and its typology are known, the challenge is to characterize them and stablish the relation to the cause that produces them so that corrective actions can be implemented in the process to avoid future occurrences. In addition, the characterization of defects is one of the most interesting research subjects and its combination with artificial intelligence tools and algorithms will result in a deep and evolutionary knowledge oriented to the continuous improvement of surface quality. Currently, the most widely used method is based on the eddy current or Foucault phenomenon. A conductive coil will generate an alternate electric current that will produce a magnetic field. When said field is in the presence of a conductive material (the material to test), an induced current (and a magnetic field) as reactive will be produced. Once both, the injection field and the induced field are known, whenever a discontinuity occurs in the inspected material, it will respond with a different signal than expected, which results in a change in impedance. It is represented and screened in a diagram, will produce a curve that is usually called “bow”. The study of these curves, their amplitudes and their phases, and the comparison with the real material is a way to characterize the defects. To be effective, the quality staff must create “alarms” or thresholds to differentiate what is a defect and what isn’t. However, this is not always easy or even possible, because locating real defects and comparing them with the signal produced quite often requires measures of parameters that sometimes are not simple such as instant speed. There is a new and sophisticated way to approach this task: it is the use of vision in combination with the eddy current. The principle is clear: whenever a defect occurs and, therefore, the eddy current detects it, a set of cameras takes an image in real time and associates and stores it with the signal for a real time or further analysis. This could seem easy, but some parameters have to be extremely well controlled such as speed, real position or depth of the defect. Nowadays, there has been a notable progress in the recognition of defect patterns only with images, it’s neither productive nor accurate, since it requires a big training and environmental cleaning conditions that are not always given in the manufacturing lines. The key, however, is not the recognition of the defects, but its real-time characterization. To do that, a combination of efforts is required: the accuracy of the eddy current system, the easy interpretation of the images and the intervention of operators and analysts to close the cycle. ISEND has developed a new non-destructive testing system called EDDYeyes for the inspection of surface quality that is made up with a combination of an eddy current equipment with direct vision cameras. Using mathematical algorithms for the treatment of big data produced, high productivity is achieved even for the most adverse conditions such as the production of hot wire rod of 4.5mm diameter and more than 120m/s. This new technology is suitable for any production process and customers that want to have the quality as identity sign.
