Common Stress Problems in Thin Walled Pressure Vessels

September 23, 2016

The curved surface of a thin walled pressure vessel flexes in response to planar stress, but design engineering excellence addresses this pressure-induced force by assessing common stress problems. A state of equilibrium is then achieved by offsetting the tug and push of opposing wall strain. It's a balancing act, undoubtedly, but this mechanical parity challenge is simplified when established system constants influence the design. Geometrical profiles and wall thickness values equate with those constants, so which external stress variables require deliberation?

Identifying and Defining Hoop Stress

This tangential stress factor runs around the circumference of the vessel due to the outward push precipitated by a pressurized fluid. The strain works at an angle perpendicular to the actual vessel wall. As with other problems of this nature, the force acts uniformly all the way around the circumference of the storage container's wall, so it is a calculable problem, one that's directly affected by the volume of the container, its flexing characteristics, and the compressibility of the storage medium.

Geometry Rules Thin Walled Pressure Vessels

There are other stressors in vessel design. Longitudinal energy is simultaneously straining the vessel while tangential hoop force pushes at the weld joints of the rolled alloy. Yet another problem, radial stress, is related to hoop problems, but the energy is proceeding outward from a central internalized force-distributing node, not making itself known as uniform circumferential strain, which is the case with hoop issues. Of course, these problems relate to a cylinder with semispheroidal end caps, so weld technology is also being subjected to some scrutiny in this scenario, especially at the end caps and the roll join.

Common Stress Problems of Fluids

Engineering science is a mix of constants and variables, all wrapped up in the close-fitting laws of Physics. We've gone some way here to determining the effects of opposing mechanical forces, but what of the fluid? Heat exchangers, for instance, add additional stress when energy is imparted to a liquid. Excess energy also causes state changes, from liquid water to steam, perhaps, or from one catalyzing chemical to another. Common stress problems, therefore, are also generated by the characteristics and energy states of the fluid medium being stored and/or processed.

A diligent design engineer constructs thin walled pressure vessels to exacting standards, shapes, and mechanical profiles. They address the various mechanical strains present and the effects of the internally stored fluid medium. Additionally, external forces and environmental stresses represent the final stressor, a factor that can cause parts to wear, contract and expand.

Contact Details

Fusion - Weld Engineering Pty Ltd
ABN 98 068 987619

1865 Frankston Flinders Road,
Hastings, VIC 3915

Ph: (03) 5909 8218

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