Recommendations + Discussions: Information on wind loads, seismic loads, snow loads, and other loads + standards + forum discussions — compiled；

This post was last edited by kareale88 on 2018-11-13 09:29; the Excel file for earthquake load calculation mentioned above is uploaded again here

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1. Load (1) Pressure: Pressure is the basic load that pressure vessels are subjected to. Pressure can be expressed as absolute pressure or gauge pressure. Absolute pressure is the pressure measured with absolute vacuum as a reference, and it is commonly used in process calculations. Gauge pressure is the pressure measured relative to atmospheric pressure. In the mechanical design of pressure vessels, gauge pressure is generally used. The pressure acting on the container can be internal pressure, external pressure, or both. The pressure in pressure vessels arises mainly from three situations: First, fluid is pumped or compressed and introduced into the vessel through pipes connected to it, thereby generating pressure, as in ammonia synthesis towers, urea synthesis towers, hydrogen storage tanks, etc.; second, a sealed vessel containing a liquid is heated, causing the liquid to expand or vaporize and thus increasing the pressure inside the vessel, as in artificial crystal production reactors; third, vessels that hold liquefied gases, such as liquid ammonia storage tanks and liquefied natural gas storage tanks, have a pressure corresponding to the saturated vapor pressure of the liquid. A container filled with liquid; the weight of the liquid generates pressure, namely hydrostatic pressure. Its size is proportional to the height of the liquid column and the density of the liquid. For example, a 10 m water column with a density of 1000 kg/m3 generates a pressure of 0.0981 MPa (which is often taken as 0.1 MPa in engineering applications). (2) Non-pressure loads Non-pressure loads can be divided into overall loads and local loads. The overall load is the load acting on the entire container, such as loads caused by gravity, wind, earthquakes, transportation, etc. Local loads are loads that act on specific areas of the container, such as piping loads, support reactions, and lifting forces. ① Gravity load refers to the load caused by the weight of the container and its attachments, internals, and contents. When calculating the gravitational load, in addition to the weight of the container itself, the weights of the insulation layer, internal components, materials, platforms, ladders, piping systems, and other auxiliary equipment supported by the container must be taken into account depending on the operating conditions. ② Wind load is the load calculated based on the effective wind pressure acting on the windward surface of the container and its attachments. It is caused by unstable flow resulting from highly turbulent air sweeping over the surface. The direction of wind flow is usually horizontal, but it may have a vertical component as it passes over the surface of obstacles. Under wind load, in addition to causing stress and deformation in the container, it may also induce vibrations along the wind direction as well as induced vibrations perpendicular to the wind direction. ③ Seismic load refers to the seismic force acting on a container, which results from the sudden vibration of the ground supporting the container and the container’s reaction to that vibration. During an earthquake, the forces acting on the container are very complex. To simplify design calculations, seismic influence coefficients are typically used to reduce seismic forces to equivalent shear forces and moments. The seismic impact coefficient is related to factors such as the soil category of the site where the container is located, the type of seismic zone, and the seismic intensity; specific values can be found in the relevant codes for seismic design of buildings. ④ Transport load refers to the forces generated by accelerations in different directions during transportation. The container is transported to the installation site by land or sea, and due to the movement of the transport vehicles or ships, the container experiences accelerations in different directions. The transport load can be expressed in terms of horizontal and vertical accelerations, or it can be represented by a coefficient obtained by dividing the acceleration by the standard value of gravitational acceleration. ⑤ Wave load refers to the load generated on containers fixed on a ship due to the acceleration caused by wave motion. The representation method for wave loads is the same as that for transport loads. The shaking load is alternating, and fatigue considerations must be taken into account; for relevant design data, reference can be made to the classification standards for ships. ⑥ Piping load refers to the load exerted on the vessel nozzles by the piping system. When the piping system is connected to the vessel nozzles, the loads generated at those nozzles due to the weight of the piping and the material inside it, thermal expansion of the piping system, wind loads, as well as seismic or other loads, are known as piping system loads. When designing a container, the overall layout of the piping is usually not yet finalized; therefore, it is not possible to conduct piping stress analysis to determine the loads at the connections. It is for this reason that the party commissioning the design of pressure vessels is often required to provide the piping loads. The container designer must ensure that the nozzles can withstand these loads, preventing excessive stress from being generated in the container or the nozzles. Once the pipeline layout is finalized, the piping designer must ensure that the loads obtained from the nozzle stress analysis do not exceed the specified pipeline load limits. (3) Alternating loads: Among the aforementioned loads, some are alternating loads whose magnitude and/or direction change over time, while others are static loads whose magnitude and direction remain essentially constant over time. Typical examples of alternating loads on pressure vessels include: i. repeated pressurization and depressurization of pressure vessels in batch production; ii. pressure fluctuations caused by reciprocating compressors or pumps; iii. changes in load on the connections due to thermal expansion or contraction of piping systems as a result of temperature changes during production; iv. variations in temperature differences between various components of the vessel; v. changes in load on the vessel’s supports caused by loading and unloading operations; vi. load changes resulting from liquid fluctuations; vii. load changes caused by vibrations (such as wind-induced vibrations). The designer should have a thorough understanding of the range of each load (i.e., the maximum and minimum values) and the number of cycles the container experiences throughout its lifetime, in order to determine whether fatigue design is necessary for the container. Alternating loads are an important factor to consider in container design; both the number of cycles with small load changes but large magnitude of change, and the number of cycles with large load changes but small magnitude of change, need to be taken into careful consideration. When designing pressure vessels, it is not necessary to take all of the above loads into consideration for each vessel. The designer should determine the design load based on the loads experienced by the inner container throughout its life cycle, in conjunction with the requirements of relevant standards and specifications. 2. Loading conditions During manufacturing and installation, normal operation, start-up and shutdown, and pressure testing, the container is subjected to various loading conditions, and the loads it endures also differ. When designing pressure vessels, the loads should be calculated separately based on different loading conditions. The load conditions that generally need to be considered include the following aspects. ① Under normal operating conditions, the loads on a container during normal operation include: design pressure, hydrostatic pressure, gravitational loads (including the weight of insulation materials, linings, internal components, materials stored within the container, platforms, ladders, piping systems, and other equipment mounted on the container), wind loads and seismic loads, as well as other loads that the container is subjected to during operation. ② Special load conditions include pressure testing, startup and shutdown, as well as maintenance operations. ⅰ. Pressure test. When pressure testing the finished containers at the manufacturing plant, the loads generally include the test pressure and the weight of the containers themselves. Usually, when conducting pressure tests in the factory workshop, the container is generally in a horizontal position. For vertical containers, horizontal testing can be used as a substitute for vertical testing. When the static pressure of the liquid column is taken into account, the pressure exerted on the top of the container is greater than that in vertical testing, which may result in insufficient wall thickness in the original design; therefore, a strength check should be conducted prior to the testing. During the hydraulic test, the hydrostatic pressure of the testing fluid and the weight of the testing fluid should also be taken into account. Under pressure test conditions, seismic loads are generally not considered. For regular inspections or other reasons, the container must undergo a pressure test at the installation site; the loads involved include the test pressure, the hydrostatic pressure of the testing liquid, and the gravitational load during the test (in most cases, the insulation material has been removed). ⅱ. Startup, shutdown, and maintenance. The loads during startup, shutdown, and maintenance mainly include wind load, seismic load, the weight of the container itself, as well as the weight of internal components, platforms, ladders, piping systems, and other equipment supported on the container. ③ Unexpected load conditions: In emergency situations such as the rapid startup or sudden shutdown of the container, chemical explosions within the container, or fires or explosions in the equipment surrounding it, the container is subjected to unexpected loads such as explosive forces and thermal shock. This article is reprinted from Pressure Vessel People