Pressure vessels wind loads

In the stress analysis of pressure vessels and pressure vessel components stresses are classified as primary or secondary. Primary stresses can be defined as those stresses that are necessary to satisfy the conditions of static equilibrium. The membrane stresses induced by the applied pressure and the bending stresses due to wind loads are examples of primary stresses. Primary stresses are not self-limiting if they exceed the yield point of the material, gross distortion, and in the extreme situation, failure of the vessel will occur. 

Any horizontal force imposed on the vessel by ancillary equipment, the line of thrust of which does not pass through the centre line of the vessel, will produce a torque on the vessel. Such loads can arise through wind pressure on piping and other attachments. However, the torque will normally be small and usually can be disregarded. The pipe work and the connections for any ancillary equipment will be designed so as not to impose a significant load on the vessel. 

Water sprays are sometimes used instead of fireproofing where the fireproofing application may be considered detrimental to the situation or uneconomical to achieve. Typical examples are the surface of pressure vessels or piping where metal thickness checks are necessary, structural facilities that cannot accept additional loads of fireproofing materials due to dead weight or wind loads, inaccessibly of the surface for application of fireproofing, or impracticability of fireproofing application. 

When an estimator costs pressure vessels such as reactors and distillation columns, care must be taken to ensure that the wall thickness is adequate. The default method in IPE calculates the wall thickness required based on the ASME Boiler and Pressure Vessel Code Section VIII Division 1 method for the case where the wall thickness is governed by containment of internal pressure (see Chapter 13 for details of this method). If other loads govern the design, then the IPE software can significantly underestimate the vessel cost. This is particularly important for vessels that operate at pressures below 5 bara, where the required wall thickness is likely to be influenced by dead weight loads and bending moments from the vessel supports, and for tall vessels such as distillation columns and large packed-bed reactors, where wind loads may... 

The walls of pressure vessels are usually relatively thin compared with the other dimensions and can fail by buckling under compressive loads. This is particularly important for tall, wide vessels such as distillation columns that can experience compressive loads from wind loads. 

We will now consider the special problems in tall tower design which are not described in the ASME Code for Unfired Pressure Vessels. As discussed previously, circumferential stresses control the design of cylindrical vessels if external loads are of small magnitude. In tall vertical vessels, four major factors (wind load, seismic loads, dead weight and vibration) may contribute to axial stresses — in addition to axial stress produced by the operating pressure or vacuum of the vessel. 

Standard calculation forms can save considerable time in pressure vessel design. These forms also systematize the mechanical design procedure to insure that nothing is omitted. Most engineering contractors have developed their own vessel calculation forms. Basically, all are alike in that they correlate, in easy-to-use fashion, the design rules set forth in Section VIII of the ASME Boiler and Pressure Vessel Code for Unfired Pressure Vessels. They also include design considerations not covered by the code, such as wind loading for tall vessels. (Text continues on p. 139.)... 

Consider a pressurized, vertical vessel bending due to wind, which has an inward radial force applied locally. The effects of the pressure loading are longitudinal and circumferential tension. The effects of the wind loading are longitudinal tension on the windward side and longitudinal compression on the leeward side. The effects of the local inward radial load are some... 

This hypothetical problem serves to illustrate how categories and types of loadings are related to the stresses they produce. The stresses which are required for equilibrium of the vessel are primary stresses. The stresses due to pressure and wind are primary general membrane stresses since even if yielding occurred, redistribution of stresses would not be possible. These stresses should be limited to the Code allowable stress values, where increases for occasional loading may be allowed for certain sections of the Code. 

Vessels will vibrate based on an exciting force such as wind or earthquake. There are two distinct types of loadings as a result of wind. The first is the static force from wind loading pressure against the vessel shell. The second is a dynamic effect from vortex shedding due to wind flow around the vessel. Tall, slender, vertical vessels are more susceptible to the effects of vortex shedding. 

The loading conditions that are generally considered for the design of pressure vessels include pressure, dead weight, piping reaction, seismic, thermal expansion and loadings due to wind and snow. The ASME Boiler and Pressure Vessel Code delineates the various loads in terms of the following conditions ... 

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