Abstract
Gamma tomography was used in this work to evaluate the recurrent defects in welding processes in naval steel sheets. It was used a first-generation equipment consisting of a source of Cesium-137, with activity of the order of 200 mCi, coupled to a Thallium-doped Sodium Iodide detector, NaI (Tl). For the study, specimens were produced in ASTM A131-AH36 steel sheets with 13.7 mm thickness; all welded by Metal Active Gas process. One reference sample was fabricated, with no macroscopically measurable defects and another welded under wind conditions producing a weld bead with different types of discontinuities. The microstructural characterization of welded joints made possible a qualitative evaluation between defective joints, in relation to the joint without defects. With the data of the tomography, 3D graphics were drawn that enabled the statistical survey and analysis of clusters of the results that allowed the localization and the dimensioning of the discontinuities that appeared as counting peaks in these graphics. It was revealed that the defective welding showed porosity of up to 39.28% of its volume, and the acceptable size crack must be less than 1 mm based on ASME-B31.3, showing the viability of the tomography for this type of nondestructive analysis.
Highlights
The joining of metallic materials has been usually accomplished by an electric arc welding process which uses heat source to melt the base metals and addition, forming a melt pool which must be protected by an inert or active gas[1]
In order to assure the quality of the welded structures it is necessary to investigate the integrity of the joint that can be made several methods of Non-Destructive Testing (NDT)
The results showed the potential of computerized tomography for inspection of defects in welded joints
Summary
The joining of metallic materials has been usually accomplished by an electric arc welding process which uses heat source to melt the base metals and addition, forming a melt pool which must be protected by an inert or active gas[1]. In order to assure the quality of the welded structures it is necessary to investigate the integrity of the joint that can be made several methods of Non-Destructive Testing (NDT). The computerized tomography (CT) gamma radiation is one of these methods that lends itself to analyze the attenuation suffered by a beam of radiation in relation to the volume of the object under analysis, allowing the acquisition of data according to the spatial density distribution[2]. Oliveira et al.[3] used gamma tomography to analyze weld defects in tubes of API 5L X80 steel. After the adequate adaptations for irradiation in flat plates the discontinuities of a welded joint of naval plates could be investigated. Microstructural characterization (destructive test) was associated for ratification of gamma-tomography (non-destructive test) results
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