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The base material for the tank containing the liquid gas (such as LNG) at below -165°C (-265°F) must remain ductile and crack resistant with the highest level of safety. The material must also permit welding without any risk of defects, for example, induced brittle fracture. Stainless steels, aluminum and 9% nickel steels can be used as they do not have a ductile/brittle transition temperature. However, in practice aluminum and stainless steel have become uneconomic for large land-based tanks but aluminum alloys are used for the large spherical tanks in gas tankers because of the lower weight. 9% nickel steel provides an attractive combination of properties at a moderate price. A high corrosion resistance is not required for LNG tanks. Steels alloyed with nickel are used in many cryogenic applications since nickel improves the quench ability and improves the notch toughness at low temperatures. Steels with 3.5% nickel, 5% nickel and 9% nickel are used at temperatures below -50°C. At temperatures below -104°C down to -196°C (-155°F down to -320.8°F) mainly the 9% nickel steels are used. The 9% nickel steel was developed in the early 40s following the “The Disaster of the Cleveland East Ohio Gas Explosion” in 1944. To learn more, please read this TOTM that discusses the incident in 1944 and the changing the metallurgical requirements for LNG Containment Tanks as a result.

The Diffusivity Equation


The theory of well testing begins with an understanding of fluid flow in porous media. In this article, the continuity equation, Darcy’s law, and equation of state for a slightly compressible liquid are used to develop the diffusivity equation, describing single-phase flow of a slightly compressible liquid.

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