Hoop stress fundamentals
For a thin-walled tube, internal pressure creates a hoop (circumferential) stress of roughly σ = P·D / (2t), where P is pressure, D the diameter and t the wall. Rearranged, the pressure a wall can carry rises with thickness and falls with diameter, bigger bores need proportionally more wall for the same rating.
Where wind angle comes in
Hoop load is carried by near-circumferential fibre, so a pressure part leans on high-angle (~85°) plies. The allowable stress used in the equation is a property of the layup, not just the material, another reason the layup is engineered to the rating.
Working vs test vs burst
A standard Fibreflow barrel is rated at 6 bar working with a 9 bar test pressure, and higher ratings are available on request. Burst sits well above test; the gap between working and burst is the safety factor, typically applied so the part never sees stresses close to its ultimate capacity in service.
Using the calculator
The pressure calculator in the Knowledge Centre gives an indicative working pressure from bore and wall so you can sanity-check a concept. Final ratings, with the exact layup, safety factor and test regime, are confirmed by our engineers on quotation.
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