# Category Archives for **Process Design**

## Elliptical and Torispherical Heads Subjected to External Pressure

The knuckles of elliptical and torispherical heads under external pressure are in tension. The critical region of these heads with regard to buckling under external pressure is the central crown, which is a spherical segment. The critical stress for buckling … Continue reading

## Spherical Shells Subjected to External Pressure

The critical compressive stress (scr) for buckling (collapse) of a spherical shell has been experimentally determined to be approximated by: where R is the radius of the sphere, and E is the modulus of elasticity of the material.

## Cylindrical Shells Subjected to External Pressure

The critical collapse pressure (Pc) of a cylindrical shell under external pressure depends on two characteristic geometric ratios: t/Do and L/Do, where t is the shell thickness, L is the unstiffened length, and Do is the outside diameter. If L … Continue reading

## Stresses in Pressure Vessel Shells Due to External Pressure

External pressure on a vessel most commonly occurs when a vacuum or partial vacuum is created inside of the vessel by (1) design, (2) discharge of its contents, (3) steam-out cleaning (condensation of steam), or (4) mechanical action, such as … Continue reading

## Pressure Vessels Thermal Stresses

Thermal-expansion problems can occur whenever there is: (1) a considerable difference between the vessel operating temperature and the temperature of the environment surrounding the vessel; (2) restricted expansion or contraction; or (3) a temperature gradient within a vessel component that … Continue reading

## Stresses from Locally Applied External Loads

Most vessels are also subject to loadings at the supports, nozzles, and attachments. These loadings produce deflections, edge rotations, shears, bending moments, and membrane forces. The effect rapidly decreases with the distance from the point of application, where the maximum … Continue reading

## Pressure Vessels Reinforced Openings

Because stresses around openings are higher than the normal design stresses for the plate thickness, additional material must be provided to carry the additional stress in the shell around the opening. The additional material provided is referred to as reinforcement. … Continue reading

## Pressure Vessels Stresses at Openings

All pressure vessels must be provided with openings to get the process fluid in and out, and to provide entry for maintenance and inspection. When a circular opening is made in a plate subjected to uniform tension, a high concentration … Continue reading

## Pressure Vessels Stress Concentrations

The normal equations for stresses in pressure vessels are based on the assumption that there is continuous elastic action throughout the member, and that the stress, for simple tension and compression, is uniformly distributed over the entire cross section. Abrupt … Continue reading

## Concentric Toriconical Reducers Discontinuity Stress

At high pressures (over 150 psi), where discontinuity stresses at the cone-to-cylinder junction can reach values above allowable limits, conical reducers having a knuckle radius at the large cylinder and a flare (reintrant knuckle) at the small end are preferred, … Continue reading