Passing a storage tank nozzle loads has been a nightmare for the most stress engineers. It does not give credit to a compression membrane stress because the tank may be empty or half.įigure 1 shows two extreme scenarios which may exist: fully restrained and semi-restrained. This increased capacity can be calculated as a new allowable stress which is used when a local tensile membrane stress exists. At the bottom of tank where the chocking exists, some parts of circumferential membrane stress capacity go to the corresponding local stresses. Radial Displacement: As mentioned earlier, due to chocking effects in the discontinuity area, the nozzles tend to move in radial direction due to thermal expansion and head pressure. Depending on the attached piping flexibility, some loads are developed at the nozzle and shell junction. Nozzle Rotation: The rotation of shell in the discontinuity area makes all nozzles rotate. Apparently all nozzles in that area are affected as follows: This takes part in a discontinuity area which is extended about, from tank base. So the displacement of that location can’t reach to its free movement. The tank base is not possible to move freely because of the base restriction. Shell course of a storage tank tends to expand due to temperature difference and head pressure.
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