Carlos Ferreira Jorge

The effect of chromium on the microstructure/toughness relationship of C–Mn weld metal deposits

Abstract Submerged-arc single-pass welds were prepared with varying chromium content in the range of 0–3.8%. Two carbon contents were obtained by dilution using different welding procedures. The variation in the chromium content was obtained by the addition of different amounts of chromium powder to the weld groove. The relationship between microstructure and toughness of weld deposits was studied by means of hardness, Charpy-V notch and metallographic tests in specimens cut transversely to the weld beads. Qualitative and quantitative analyses of microstructural constituents and fine phases were made by light optical and scanning electron microscopy, respectively. In this investigation, a selective etching method was employed in order to distinguish the martensite–austenite (M/A) “microphase” constituent from carbides. The results show that chromium impairs impact toughness, although it promotes an increase in the percentage of acicular ferrite (AF). In addition, it was observed that an increase in carbon content promoted a further decrease in impact toughness due to the higher volume fraction of the M/A constituent.

Comparative study of high-strength steel weld metals obtained by the SMAW and FCAW processes for offshore applications and mooring chains

A comparative study of the clad electrode and tubular wire processes was carried out, looking at the mechanical and micro-structural properties of weld metals of high-resistance steel, in the ‘as-welded’ and ‘stress-relief heat treatment’ (PWHT) conditions. The results show that the procedures adopted for welding with tubular wire and clad electrodes allow satisfactory levels of mechanical resistance to be obtained, with the exception of the value of percentage lengthening of the tubular wire, in the as-welded condition. The impact tests show that both the weld metals showed satisfactory impact resistance, in both the as-welded and PWHT conditions, observing that, for the tubular wire, the impact resistance is lower for the clad electrode in both conditions, lying close to the limit applied for the acceptance criterion of 50 J at 0°C in the PWHT condition. It was confirmed that the productivity achieved by the tubular wire process was approximately twice as high as that for the clad electrode process. As a result, the inherent advantage of the tubular wire process must be complemented with a consideration of all the mechanical properties obtained, orienting suitable selection of the welding process, in particular, for application in equipment that operates in fatigue conditions.

Effect of post-welding heat treatment on the mechanical and microstructural properties of extra high-strength steel weld metals, for application on mooring equipment

Evaluation was performed of a weld metal with tensile strength higher than 860 MPa for welding R4 grade steel of standard W22 of the International Association of Classification Societies, Ltd. Multipass joints were welded with preheating at 200 and 250°C, using the coated electrode process with a 4.0-mm-diameter consumable, the basic composition of which was: C – 0.06%, Mn – 1.89% and Ni – 2.95%. After welding, mechanical and metallographic tests were performed on samples entirely removed from the metal deposited in conditions as-welded and after post-weld heat treatment performed at 600°C for 2 h. The results show that the weld metals obtained have mechanical properties suitable for all conditions of analysis, providing properties superior to the minimum required for welding R4 grade steel used on petroleum platform mooring equipment. The metallographic analysis enabled identification of the microstructure and explanation of the behaviour of the mechanical properties after post-weld heat treatment.

Propriedades mecânicas e microestruturais de juntas soldadas do aço HY-80 pelos processos eletrodo revestido e GMAW

The welding of high strength steels represents a continuous challenge taking into account the great variety of alloys systems, which present stringent requirements of high strength and toughness. Into this context the HY-80 steels largely employed in the Naval Industry are still welded preferentially by the SMAW process, despite its limitations when compared with other welding processes. In order to promote an improvement on productivity, the present work presents a comparative analysis between the mechanical properties of the HY-80 welded joints performed by the GMAW and SMAW processes. Multipass welding by shielded metal(SMAW) arc and gas metal arc welding (GMAW) processes were performed with preheating and inter-pass temperatures of 90°C and 150°C respectively in plates of dimensions 850X150X30 mm in HY-80 steel, in the flat position and average energy welding of 1.29 for SMAW and 1.36kJ/mm for GMAW process. After welding a post weld heat treatment at 600°C for 1 hour was performed, this condition being compared with the as welded condition. Tensile, Charpy-V notch and hardness tests and metallographic examination by scanning electron microscopy were performed for mechanical and microstructural characterization. Additionally, it was carried out a comparative analysis between processes. The results show that it is possible to achieve adequate mechanical properties for all analyzed conditions. Furthermore, it was observed that the productivity provided by the gas metal arc welding process was greater than shield metal arc welding.

Efeito do tratamento térmico pós-soldagem nas propriedades mecânicas e microestruturais de metal de solda de aço de extra alta resistência para utilização em equipamentos de ancoragem

A weld metal with tensile strength higher than 860 MPa for the welding of a IACS W22 R4 Grade Steel was evaluated. Welded joints with preheat of 200 and 250oC were produced by SMAW process using 4.0 mm diameter covered electrodes in multipass technique whose basic composition was: C-0,06%, Mn-1,89%, e Ni-2,95%. After welding, mechanical and metallographic tests were done in all-weld metal samples in both as-welded and post welded heat treatment conditions performed at600oC for 2 hours. The results show that the obtained weld metals have mechanical properties higher than the minimum required for the welding of a IACS W22 R4 Grade steel in all condition analysis, which makes possible to attain an adequate strength/toughness relationship for high strength steel applied in mooring equipments. The metallographic analysis allowed the identification of microstructure and, consequently, the behavior of the mechanical properties after post weld heat treatment.

Assessment of nickel alloy 625 weld overlays deposited by the electroslag process

Abstract Nickel-base alloy weld overlays are commonly used in the oil and gas industry to extend the life of equipment under aggressive corrosion environments, since the overlays improve the corrosion resistance without a significant increase in the cost of manufacture when compared to massive equipment. Usually, the joints are welded by SMAW, GMAW or GTAW processes. In this respect, the electro slag welding process (ESW), which promotes high heat inputs and low dilution welds, can be an interesting option for this application as it provides high productivity as only one layer is necessary. The present work evaluates mechanical, microstructural and corrosion properties of an Alloy 625 weld overlay deposited on ASTM A516 Grade 70 carbon steel by the ESW process. The deposition was done with one and two layers in plates of dimension 50 mm × 400 mm × 400 mm, in the flat position and an average energy welding 11.7 kJ/mm. After welding, a post-weld heat treatment at 620 °C for 10 h was performed, this condition being compared with the as-welded condition. Bending tests showed no evidences of cracks. Microstructural evaluation performed using both optical (OM), scanning (SEM) and transmission electron microscopy techniques showed an austenitic microstructure of the weld deposit with a low proportion of secondary phases for all conditions, and the post-welding heat treatment did not promote significant changes in the mechanical properties. At the coarse grain heat-affected zone (CGHAZ), the occurrence of proeutectoid ferrite, pearlite and bainite were found for one layer deposit and refined pearlite and ferrite for two layer deposits where the microstructural constituents were observed due to the low cooling rate. In addition, no evidence of partially diluted zones (PDZ) were verified. Corrosion tests conducted on samples removed from the top layer of the weld overlay cladding deposit according to ASTM G 48 Method A Standard were considered satisfactory once no evidence of pittings was verified and the loss of mass was very much reduced.

PROPRIEDADES MECÂNICAS DE UMA JUNTA DE AÇO C-Mn SOLDADA PELO PROCESSO HÍBRIDO LASER-GMAW

Resumo O processo de soldagem híbrido LASERGMAW, comumente designado por HLAW (Hybrid Laser Arc Welding), foi concebido há bastante tempo, mas só recentemente começou a ser aplicado industrialmente. Nesse trabalho foi feita uma avaliação do seu desempenho na soldagem de chapas de aço C-Mn com 10mm de espessura. As juntas produzidas foram avaliadas por meio de ensaios de impacto Charpy-V e mapeamento de microdureza Vickers, além da caracterização microestrutural. Também foram realizadas, medições dos níveis das tensões residuais introduzidas na junta soldada pelo processo híbrido, comparativamente com o processo GMAW robotizado. Os resultados da avaliação de desempenho do processo híbrido mostraram uma maior produtividade em relação ao GMAW robotizado. As propriedades mecânicas da junta soldada se mostraram compatíveis com os requisitos do material de base. Palavras-chave: Soldagem Híbrida; MIG-Laser; Aço C-Mn

Estudo comparativo de metais de solda de aço de alta resistência obtidos pelos processos eletrodo revestido e arame tubular para aplicação em equipamentos de amarração offshore

Realizou-se um estudo comparativo entre os processos eletrodo revestido e arame tubular, considerando-se as propriedades mecânicas e microestruturais de metais de solda de aco de alta resistencia, nas condicoes de como soldado e com tratamento termico de alivio de tensoes (TTAT). Os resultados mostram que os procedimentos adotados para soldagem com arame tubular e eletrodos revestidos possibilitaram obter niveis de resistencia mecânica satisfatorios, com excecao do valor de alongamento percentual para o arame tubular, na condicao de como soldado. Os ensaios de impacto mostram que ambos os metais de solda apresentam tenacidade ao impacto satisfatoria, tanto na condicao de como soldado quanto na de TTAT, observando-se que, para o arame tubular, a tenacidade ao impacto e inferior a do eletrodo revestido em ambas as condicoes, situando-se proximo ao limite do criterio de aceitacao aplicado de 50 joules a 0oC, na condicao de TTAT. Verificou-se que a produtividade propiciada pelo processo arame tubular foi aproximadamente duas vezes superior ao processo eletrodo revestido. Desta forma, a vantagem inerente ao processo arame tubular deve ser complementada pela consideracao do conjunto das propriedades mecânicas obtidas, orientando a selecao adequada do processo de soldagem em particular para aplicacao em equipamentos que operam sob condicoes de fadiga.

Finite Element Residual Stress Analysis Applied to Offshore Studless Chain Links

The increasing expansion of deepwater petroleum activities has resulted in new challenges to the design of mooring systems. The complex mooring systems load history, which consists in a combination of wind, waves and currents, could induce nucleation and propagation of cracks in mooring line components. The failure of a single element in a mooring line of an offshore oil exploitation platform can produce incalculable environment damage as well as human and material losses. Offshore mooring line components like chain links must be submitted to a mandatory proof test, dictated by offshore standards, where loads higher than operational loads are applied to the mechanical component, resulting in high levels of residual stresses. Nevertheless, its presence is not considered in traditional design methodologies. Therefore, it is fundamental to develop new and more precise methodologies for assessing the structural integrity of mooring components. In this article, a comparative study is developed considering different approaches: two bidimensional finite element models, two tridimensional finite element models and an analytic model. These analyses establish the drawbacks and goals of using simpler models in the prediction of studless chain links stress distributions and in their fatigue lives. The four finite element models consider large displacements, plasticity and contact phenomena. Moreover, a simple fatigue life analysis is presented, based on SN curve, considering the effect of residual stresses in studless chain links before operation, that is, with loads caused by the proof test.Copyright

Analysis of the Influence of Mechanical Properties on the Residual Stress in Offshore Chain Links Using the Finite Element Method

Production offshore units have a relative long operational life (about 20 years), during which are submitted to the ocean adverse environment loading produced by the combination of wind, waves and currents. This complex loading history can promote the nucleation and propagation of cracks in mooring line components. The presence of defects establishes a critical situation that can lead to catastrophic failures. In spite of residual stress plays a preponderant part in the structural integrity of a mechanical component, the presence of residual stress is not considered in traditional design of these mechanical components. Therefore, is fundamental to develop new and more precise methodologies for assessing the structural integrity of mooring components. The present contribution regards on modeling and simulation of the residual stress distributions in studless chain links using a tri-dimensional elastoplastic finite element model with large displacements. In the analysis three material conditions, associated with different mechanical properties, were considered. The results indicate that the presence of residual stresses modify significantly the stress distribution in the component. Also, residual stress distribution depends on the mechanical properties of the chain link material. The structural integrity of the mechanical component was studied using the concept of critical volume associated to the material volume susceptible to a certain critical crack size. This methodology permits the evaluation of the critical crack length distribution related to brittle fracture of the component.© 2003 ASME