Reasonable care must be taken in handling and use to protect glass (quartz) surfaces from scratches, abrasions, pits or digs that can act as break sources. Glass under stress will fail due to a break source. Therefore, surface preparation of glass exposed to thermal or mechanical stress is critical. Alternately, defects that are smooth and exhibit a gentle surface change are less damaging. This calculator is based on accepted strength of material calculations for the geometry and conditions selected. It assumes good workmanship in the manufacture of components. The calculator should in no way be interpreted as a guarantee or a warranty of the quartz performance. It should be used along with prudent testing of designs.
This calculator can be used to determine the required wall thickness or the allowable internal pressure for a fabricated pressure vessel at low temperatures.
This calculator uses the thin wall approximation that is applicable when the wall thickness is less than about one twentieth of the diameter. (The thickness is less than .05 * diameter.) This approximation can provide some information about allowable internal pressures. The use of this approximation on thick wall cylinders is intended for relative comparisons, only. All designs should be evaluated using thick wall techniques that include radial stress distributions.
The calculator uses the relationship between the radius, thickness, and the applied internal pressure to determine the tangential (hoop) stress. The longitudinal stress is half of the tangential stress, so it is not calculated. These relationships only apply to sections of the pressure vessel significantly distant from the ends, since various nonlinearities and stress concentrations exist near these ends.
This calculator only considers internal pressure. Pressure vessels under external pressures must be analyzed for buckling and other modes of failure.