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A dosage methodology for lime-treated soils has previously been established based on rational criteria where the porosity/lime ratio plays a fundamental role in the assessment of the target unconfined compressive strength (qu). The present research extends this previous work by quantifying the influence of the amount of lime, the porosity and the porosity/lime ratio in the assessment on tensile strength (qt) of soil–lime mixtures, as well as in the evaluation of the qt/qu relationship. A programme of splitting tensile tests and unconfined compression tests considering three distinct dry unit weights and four lime contents, varying from 3 to 9%, was carried out in the present study. The results show that a power function fits qt and qu values well with increasing volumetric lime content and a power function fits qt and qu values well with reducing porosity of the compacted mixture. The porosity/lime ratio is demonstrated to be an appropriate parameter to assess both qt and qu of the silt–lime mixture studied. Finally, the qt/qu relationship is unique for the silt–lime studied, being independent of the porosity/lime ratio.

Underwater wet welding (UWW) with shielded metal arc welding (SMAW) is employed basically in repairs of offshore structures, including platforms, ships and others. The main problems of this type of welds are related, of course, with water presence in the electric arc that causes higher cooling rates, Oxygen and Hydrogen availability in the arc atmosphere and arc instability. Many of research and test welding programs in laboratory are undertaken in shallow water performed by automatic devices using hyperbaric chambers to simulate depths. Also, welding arc signals are acquired using data acquisition systems and the arc stability is estimated through indexes calculated from values acquired and analyzed. It is very well known the reduced stability of the wet welding process at shallow depths — less than approximately five meters. So this effect would be considerable significant since it can be used to make correlations between the arc stability indexes and the welds quality results. The main objective of this work was to evaluate the efficiency of the most used arc stability indexes reported in the literature in detect the arc instability effect of shallow water wet welding. Bead-on-plate welds had been made using a gravity feeding system device inside a hyperbaric chamber, applying straight polarity (DCEN) in ASTM A36 steel plates, using the same weld parameters in two different depths, 0.5 and 20.0 meters. Rutile, basic and oxidizing commercial electrodes types prepared for UWW with 3.25mm rod diameter were used. Visual analysis, bead morphology and arc stability were the criteria used to evaluate the weld quality. The voltage and current arc signals were acquired at 10 KHz rate. The arc stability indexes measured were average voltage and current and its standard deviation, S (Imax/Imin) parameter, voltage and current square mean, arc “re-ignition” voltage and current, metal transfer time and its deviation, metal transfer frequency and its deviation, short circuit time and its deviation and the voltage versus current graph area. The results shown that none of the stability indexes tested has been shown to indicate, alone, a good relationship to the surface appearance obtained for the three electrodes studied. The rutile type electrode was the only one that clearly produced better weld appearance at 20 meters than in shallow water depth. The rutile and oxidizing electrodes showed better surface appearance with the increased number of short circuits. For the rutile electrode, the globular transfer mode with high voltage were directly related with poor weld bead surface appearance.

propriedades mecânicas satisfatórias até 11,1 MPa (1) e até 25 MPa. (2) Entretanto, são pouco conhecidos as influências e os limites operacionais dos gases ativos, principalmente do oxigênio e do dióxido de carbono, adicionados no gás de proteção. INTRODUÇÃOEstudos recentes sobre propriedades mecânicas e metalúrgicas de soldas MIG/MAG hiperbáricas mostraram que a combinação de arame sólido e argônio como gás de proteção é capaz de produzir soldas isentas de defeitos, na posição plana, com

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The use of oxidizing electrodes for wet welding of offshore structural steels, in spite of their low susceptibility to hydrogen HAZ cracking, is limited, in part, by the poor mechanical properties of their weld deposits. Low levels of carbon, manganese, and other deoxidizers, together with high oxygen contents seems to be one of the reasons for this low performance. This work investigated the influence of nickel additions on the tensile strength and impact resistance of wet welds deposited at 1.1 m of water depth. It was found that welds with nickel contents between 2 and 3 weight percent exhibited maximum toughness and tensile strength. Nickel additions also had a strong effect in reducing the grain size of equiaxed ferrite in the reheated region of underwater wet welds, thereby improving their mechanical properties. The drop of mechanical properties for nickel contents higher than 3 weight percent was associated with weld metal solidification cracking.

Resumo Por sua grande versatilidade e baixo custo, SMAW é considerado o processo de maior uso na indústria naval e offshore. Porém, como resultado de ter o arco elétrico em contato direto com o meio aquoso, o emprego da técnica é exposto à pressão hidrostática agindo na coluna de arco e na poça de fusão, assim como também, à dinâmica de geração de bolhas e a decomposição da água. A combinação destes fatores influencia na estabilidade do processo, resultando em cordões de solda com grandes quantidades de defeitos. Neste ponto em particular, destaca-se que a definição de estabilidade em UWW encontra-se pouco compreendida, fato pelo qual existem diversas opiniões na indústria e na literatura, sem ter-se explicação do fenômeno. Assim, este estudo caracteriza a estabilidade em função de uma das características elétricas do arco: a polaridade. A configuração deste último fator define as características resultantes na junta; deste modo, os fenômenos de catodo e anodo que governam a geração de calor influenciam no formato do cordão ou na taxa de fusão do consumível. Nesta pesquisa, foram utilizados um eletrodo rutilico comercial e um consumível que apresenta resultados promissores em matéria de propriedades mecânicas e teor de Hidrogênio Difusível: WW70.