Category: Mechanical and Structural

Horizontal Vessels Saddle Supports and Stiffening Rings

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Horizontal vessels are typically supported on two saddles. The use of two saddles is preferred both statically and economically over a system with more supports. The vessel designer should follow these steps: 1. Locate the position of saddle supports. 2. Calculate the maximum support reactions and corresponding allowable shell stresses. 3. Provide circumferential stiffening rings […]

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Horizontal Ring Girders

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Ring girders are typically used in elevated vessels when they are supported by a structural frame. The stress distribution in a ring girder is very complicated. Given a uniform load around the perimeter, the stresses and forces can be calculated given the following assumptions: • Supports equally spaced • Vertical deflection at supports is zero […]

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Vertical Vessel Lug Supports

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Vertical Vessel Lug Supports

The main design consideration regarding lug-supported vessels is the stress magnitude in the shell. Bijlaard’s method, as covered in WRC 107, is usually followed for the design. This method consists of determining the stress in the shell at the vicinity of a support lug of height 2C2 and width 2C1, as shown in Figure 400-20. […]

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Vertical Vessel Support Legs

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Support legs can be made of wide-flange or pipe members. They are designed to resist axial loads, overturning moments, and lateral shear forces in the vessel. The attachment point to the vessel may cause high concentrated shell stresses which must be investigated by a qualified vessel designer. The allowable stress in the member may also […]

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Openings in the Skirt

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Openings in the Skirt

For skirt compression, deduct the width of openings, G (ft), around the perimeter of the skirt. The following equations take into account the shift in the neutral axis as well as the reduction in cross section. The equation for maximum compressive stress f under combined axial and bending loads at openings can be written: where: […]

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Vertical Vessel Skirts

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Vertical Vessel Skirts

The design procedure outlined here is based on cylindrical skirts. (Tapered designs are a special problem and beyond the scope of this manual.) Design of the skirt consists of determining the operating weight of the vessel and the controlling bending moment due to wind or earthquake. The skirt thickness should be checked at three locations: […]

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Structural Supports

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Structural Supports

Process vessels are normally supported by one of the following methods (See Figure 400-19): • Skirts • Support legs • Support lugs • Ring girders • Saddles Skirts are typically used for vertical vessels because they are the most economical. Leg-supported vessels are normally lightweight, and the legs provide easy access to the bottom of […]

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Internal Appurtenances Loads

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For both vertical and horizontal vessels, internal appurtenances create loads that are directly applied to the vessel shell. These design concerns are best handled by the vessel designer, with input from engineers familiar with the process technology. (See below for examples.) For vertical vessels, trays are typically used to support catalyst or bubble caps. These […]

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Horizontal Vessels Wind and Earthquake Loads

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Horizontal Vessels Wind and Earthquake Loads

In horizontal vessels, wind and earthquake loads primarily affect the design of saddles and supports. The design of the shell is normally controlled by other loads such as design pressures, operating weight, saddle reactions, etc. A horizontal cylindrical vessel supported by two saddles acts like a uniformly loaded, simply supported beam. Vessels with hemispherical or […]

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Moment Amplification

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Moment Amplification

Certain “slender” vessels are susceptible to increased stresses as a result of the eccentricity of the vessel weight in the deflected position. Slender vessels are defined as vessels with one of the following conditions: 1. Uniform diameter, and uniform mass distribution, with a height-to-diameter (H/D) ratio exceeding 30. 2. Non-uniform vessels with large loads concentrated […]

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