PSI - Issue 11

Hizadora Constanza Medina D’Ambros et al. / Procedia Structural Integrity 11 (2018) 114–121 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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1. Introduction

Welding is a joining process of two or more metallic components involving melting of the metal adjacent to the joint to establish an atom-to-atom bond (Hellier, 2003). In the Shielded Metal Arc Welding (SMAW) process an arc welding process produces coalescence of metal by heating them with an arc between a covered metal electrode and the working surface (Ranjan, 2014). The quality of the weld and its mechanical strength depends on the interaction of variables, as joint temperature and pression. In SWAN process not all of the properties are related with materials properties (Ranjan, 2014). Since that, parameters of interest in arc welding include: welding current, welding voltage, welding speed, torch position, gas protection, filler material addition and wire feed speed (Sun et al., 2005). However, is difficult control and maintain these parameters constant when the welding outside the laboratorial environment. The difficulty of completely controlling the welding process predict the presence of defects at welds (Rogerson, 1983), the failures will inevitably exist in welded structures (Maddox, 1974). According to Rogerson (1983), there are two groups of defects: technological and workmanship defects. The first defect results from inconsistency in the welding operations, and the second defect are from the inherent variability of the welding process. Because of this is necessary define reliable methods of assessing the significance of failures and also acceptance levels of weld defects (Boulton, 1976). Some non-destructive testing (NDT) techniques used to assurance quality in weld joint are: visual inspection, dye penetrant inspection, magnetic particle testing, radiographic inspection, ultrasonic testing. The quality levels for imperfections are determined by standardizations as BS EN ISO 5817:2014 (ISO, 2014). The damage caused by the defects in butt-welded joints were evaluated by authors as Chang and Teng (2004) who investigated the residual stresses of this type of weld, considering a no uniform temperature distribution, thermal strains and localized plastic deformation causes by the welding process. In the same way, the effect of weld geometry and residual stresses on fatigue in butt-welded joints was the object of Teng et al (2002) in order to predict the effects of important butt weld geometry parameters. Steel water elevated reservoir localized in the state of Tocantins, Brazil, was visited to discover the existence of welded joints pathologies by visual analysis. The study was carried out by water supplier company's invitation which aimed to reduce the failures numbers in these structures once several times the loss of water in steel water elevated reservoir had happened at the weld joint. Structures in the communities Paraíso do Tocantins, Porto Nacional and Araguatins were visited, the Fig. 1 show the location of these cities.

Fig. 1. Location of visited cities with steel water elevated reservoir and the welder in Paraíso do Tocantins, Porto Nacional and Araguatins.

Damages found at welded joints by visual analysis were related to slag inclusions, high and low welding amperage and also moist welding electrodes, the Fig. 2 and 3 show the aspects of this pathologies. The presence of slag inclusions characterized this pathology, but also defects as overlap, excess weld metal, porosity were identified (Fig. 2).