Skirt attachment

Note If flush skirt attachment is preferred, weld attachment can be considered using prescribed design procedures. 

In summary, all portions of the reactor vessel wall that are covered by water would be adequately protected against failure by melting or creep rupture. For the cases with no venting or partial venting of the support skirt, the creep rupture failure is predicted to occur in the portion of the vessel wall adjacent to the trapped gas pocket beneath the skirt. Partial venting would reduce the size of the gas pocket and delay the predicted time of failure, but the failure mechanism would still be creep rupture beneath the skirt attachment weld. With complete venting, however, there would be no gas pocket and this failure mechanism would be eliminated. 

Creep rupture of the vessel bottom head beneath the support skirt attachment would release debris into the water-filled pedestal region to fall downward onto the drywell floor. Since containment flooding would provide a water depth of more than 30 feet (9.144 m) over the drywell floor, the particulate matter released from the debris mass should be adequately scrubbed provided, of course, that violent steam explosions do not occur. Furthermore, the lar volume of water in the drywell would protect the diyu ell shell from late failure in Mark I containment... 

Integral pipe attachments are welded directly to the pipe and are usually of special design. They are used in high temperature services, with moderate or severe loads, and in conjunction with supports, braces, and restraints where rigidity with the pipe shell is desired. Integral attachments may be grouped into five types ears, lugs, shoes, cylindrical tmnnions, and skirts (see Fig. 8). 

Wind loading will only be important on tall columns installed in the open. Columns and chimney-stacks are usually free standing, mounted on skirt supports, and not attached to structural steel work. Under these conditions the vessel under wind loading acts as a cantilever beam, Figure 13.19. For a uniformly loaded cantilever the bending moment at any plane is given by ... 

The dress was in a disassembled state when donated, such that the bodice and skirt portions were no longer attached and the once totally enclosed waistline seam allowance was exposed. A piece of what is believed to be a remnant of the original fabric from which the dress was made was also included in the donation. A visual comparison of the... 

The method used to support a vessel will depend on the size, shape, and weight of the vessel the design temperature and pressure the vessel location and arrangement and the internal and external fittings and attachments. Horizontal vessels are usually mounted on two saddle supports see Figure 13.20. Skirt supports are used for tall, vertical columns see Figure 13.21. Brackets, or lugs, are used for all types of vessels ... 

In designing the skirt, no consideration is required for the vessel s operating pressure since the skirt is not under pressure or vacuum loading. Since the skirt is an attachment rather than a part of the pressure vessel proper, the allowable stresses specified by the ASME Code need not be used. 

One of the most common methods of supporting vertical pressure vessels is by means of a rolled cylindrical or conical shell called a skirt. The skirt can be either lap-, fillet-, or butt-welded directly to the vessel. This method of support is attractive from the designer s standpoint because it minimizes the local stresses at the point of attachment, and the direct load is uniformly distributed over the entire circumference. The use of conical skirts is more expensive from a fabrication standpoint, and unnecessary for most design situations. 

The critical line in the skirt support is the weld attaching the vessel to the skirt. This weld, in addition to transmitting the overall weight and overturning moments, must also resist the thermal and bending stresses due to the temperature drop in the skirt. The thinner the sldrt, the better it is able to adjust to temperature variations. A hot box design is... 

There are various methods of making the attachment weld of the skirt to the shell. The preferred method is the one in which the center line of the shell and skirt coincide. This method will minimize stresses at the juncture. Probably the most common method, however, is to make the OD of the skirt match the OD of the shell. Other methods of attachment include lap-welding, pedestal type, or a shear ring arrangement. The joint efficiency of the attachment weld also varies by the method of attachment and is usually the governing factor in determining the skirt thickness. This weld may be subject to cracking in severe cyclic service. 

Because the skirt is an attachment to the pressure vessel, the selection of material is not governed by the ASME Code. Any material selected, however, should be compatible with the vessel material in terms of weldability. Strength for design is also not specified for support material by the ASME Code. Usually, in the absence of any other standard, the rules of the AISC Steel Construction Manual will be utilized. For elevated temperature design, the top three feet of skirt at the attachment point should be of the same material as the shell. 

P = maximum anchor bolt force, lb Pi = maximum axial force in gusset, Ib E =joint efficiency of skirt-head attachment weld... 

Thickness required at skirt-head attachment due to M,. Longitudinal forces... 

Anchor Bolt Chairs Gussets and plates welded to base plate and skirt to provide for anchor bolt attachment. 

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