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Many applications operate at sufficiently low temperature conditions where most structural steels become very brittle and, therefore, unsuitable for use in safety-critical structures. So the materials used in the vessels or storage tanks which keep the natural gas at liquefaction temperatures need to remain ductile and crack resistant with a high level of safety. The material also needs to have high strength in order to reduce the wall thickness of the container and it must permit welding without any risk of brittle fracture. 9% Ni steel plates are one of most common used materials in the LNG storage tank application. However, the welding procedure for 9% Ni steel plates requires high level of skills of welding that is strictly controlled welding parameter for balancing avoidance of cold and hot cracking and maintenance of high strength. Mechanical properties are important characteristics of the weldment that must confirm to the application feasibility as well as functional requirements of the welded joint. The only way to enhanced the mechanical properties of welded joint by controlling the parameters of using welding process. From the main variables of the arc welding process are the heat input and interpass temperature where the two variables control the thermal cycle of welding process. The experiment show that for thin test specimen with thickness ≤ 14 mm, the heat input range from 1.4 to 2 KJ/mm and controlling interpass temperature within 80°C give high tensile strength with improving the toughness properties of welded joint and reduce the probability of brittle fracture happened by increase the ductility and reduce the yield strength and increased the transition temperature.

The need for an alternative to steel reinforcement (RFT) in areas of severe environmental conditions and areas sensitive to magnetic fields has emerged the use of Fiber Reinforced Polymers (FRP). Experimental and analytical studies of FRP reinforcement are still less than that of steel RFT. In this study, seven slabs reinforced with local Glass Fiber Reinforced Polymers (GFRP) were tested under four points bending configuration. Load-deflection behavior, as well as strains in slabs, was recorded in order to investigate slab's ductility and flexural behaviors. The main parameters of the experimental work included RFT ratio, and shear span to effective depth ratios (L sh /d eff .) Analytical models used to predict these behaviors were implemented in order to compare the results with experimental work. The results of this research work indicated that crack behavior and load deflection curves can be simulated using analytical models and can be reasonably used for the prediction of the behavior of the tested slabs.