An Overview of Hoop Stress and Stress Attenuators in a Pressure Cylinder

April 13, 2021

Hoop stress is a circumferential fluid load variable that all thin-walled pressure cylinders must be designed to handle. Pushing outward, that internal stress factor forces the curving walls of the alloy-strengthened cylinder to bulge and expand outward.

If the internal strain wasn't counterbalanced, the seams of the cylinder could burst due to the inexorable expansion effect. Let's take out our virtual X-Ray machine and see how these circumferential forces work.

The Basics of Hoop Stress in a Pressure Cylinder

Multidirectional fluid forces push and tug at pressure vessels. It's the engineer's job to isolate these potentially destructive energies and analyse their behaviour. Longitudinally, there are the actions of the pressurized medium as it tests the limits of the hemispheroidal end caps welded to the cylinder. Hoop forces, however, operate on a separate axial plane.

In other words, while that former example pushes from one end to the other, the forces we're studying are working out towards the curved walls of the cylinder, where they press against that sheet steel surface and stress the weld seams. In order to counter these forces, we have engineering mathematics. It's these geometry-based formulae that imbue the cylinder material and its general architecture with a design-incorporated stress mitigation feature.

Stress Attenuators in a Pressure Cylinder

Granted, the hoop stress management maths allows the engineer to virtually convert the curved metal walls into a single, easy to assess surface, but what comes next? Well, after the axially directed wall strain is distilled into a mathematical function, some real world engineering action is next on the agenda.

If this remedial action was to be skipped, weld seams would rupture, fractures would occur in the walls of the cylinder, and a possibly catastrophic event would trigger alarms across the processing facility. We integrate that abstract mathematical function by altering the geometry of the cylinder and by employing a stronger material base, a graded alloy that's accompanied by a similarly fortified proceduralism that boosts the weld procedure and all other metal worked stages of the project.

Cylindrical pressure vessels are vulnerable to hoop stress. Simply put, the long loops of rolled metal extending between two end caps are continually exposed to internally propagating fluid forces. Operating along an axial plane, the stress tests the metal sheets, pushes the alloy so that it expands then contracts.

But the design engineers account for this sheet bulging effect by integrating a geometrically translated counteraction mechanism into the pressure vessel's build, one that acts as a fluid load overhead feature that accounts for this internally-sourced expansion effect.

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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