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.

Residual stresses on welded joints have been studied by several methods. In this present work, residual stresses was measured by a novel methodology under development named Displacement of Coordinated Points (DCP). To evaluate anisotropy effects in steel plates, two directions of the weld bead were considered: Welding was performed in both parallel and transversal direction of rolled steel plate ASTM A131 grade AH36.The experiments showed higher values of the residual stress in the transversal direction of the lamination when compared with the longitudinal direction, evidencing the anisotropy effect of the material. It was also observed that the increasing in heat input induces higher residual stress.

Choosing welding parameters is an important step in welding process, directly influencing in the heat input provided to welded joints. This heat input value, along with temperature distribution in welded joints, provides, to the drafter, conditions of predicting the Heat Affected Zone (HAZ) extension, the kind of microstructure to be formed, and therefore, the effects of residual stress. Three welding parameters were switched, providing different welding conditions. Each condition was analyzed by SmartWeld 2011 software and macrography to find and compare the extension of HAZ. As for the residual stresses, calculated through Displacement of Coordinated Points (DCP) method. It is possible to choose the best parameters for the welded joint by GMAW process considering the parameters in study.

The lamination process adds the anisotropy characteristic in the final product. This anisotropy influences the yield strength according to the direction in question, the difference between the value of the yield tension in one direction and the value of the yield tension in another direction referred to as the back stress. Naval plates were welded by the GMAW process in the longitudinal direction to the lamination and in the transverse direction, and with different thermal loads. The residual stresses were calculated by displacement coordinate points method (DCP) and the back stress was found by tensile tests in specimen subjected made with either the longitudinal lamination direction and transverse lamination direction. The material used was ASTM A131 naval steel grade AH-36. The welded plates with greater thermal load in the longitudinal direction presented smaller residual stress in this direction, in relation to the transverse lamination direction. In the welded plates with greater thermal load, in the transverse lamination direction, the displacements in different directions were close, showing that the back stress does not act reversing the displacement (flow). Finally, for the welded plates with lower thermal load, both welded in the longitudinal and transverse direction, the displacements were small. In addition, the back stress did not act reversing such displacements.