Pressure-equipment design engine for mechanical and vessel engineers: cylindrical shell per UG-27 (circumferential and longitudinal governing logic), formed heads per UG-32 (2:1 semi-elliptical, torispherical with M-factor, hemispherical), joint efficiency by radiography class, corrosion allowance on a corroded-basis radius, validity window P ≤ 0.385·S·E, standard plate selection, MAWP back-calculation and hydrostatic test pressure per UG-99 (1.3× stress ratio). Every input with selectable universal units, every report with the full audit trail.
SectorCalc SC-033 sizes pressure-vessel shells and heads per ASME VIII Division 1 internal-pressure rules: UG-27 for the cylinder (governing of circumferential and longitudinal stress), UG-32 for 2:1 elliptical, torispherical and hemispherical heads, with joint efficiency, corrosion allowance on a corroded-basis radius, plate selection, MAWP back-calculation and the UG-99 hydrotest pressure. Scope is deliberately limited to internal pressure on seamless-or-butt-welded cylinders — nozzles, external pressure, cyclic service, flange and support design are separate code chapters. All output is pre-design grade: the Manufacturer's Data Report signed by an Authorized Inspector is the only legal design verification.
The circumferential (hoop) case governs in virtually every vessel — hoop stress is twice longitudinal stress in a cylinder, which is why vessels split along their length, never around their girth. The engine computes both and takes the maximum, then adds CA and rounds UP to standard plate.
A 2:1 elliptical head needs almost exactly the shell thickness — that kinematic coincidence is why it dominates industry. Torispherical heads with M ≈ 1.54 (L=D, r=0.1D) pay a 54 % thickness penalty in the knuckle; hemispherical heads halve the stress but cost forming depth and vessel height.
E scales the allowable directly: moving from no-RT (0.70) to full RT (1.00) buys 43 % thickness margin — often cheaper than the plate it saves on large vessels. UW-12 values assume Type 1 butt welds; backing strips left in place, fillet-welded construction and non-code welders void the table. Head seamless vs welded matters too: the engine applies E to all head formulas, the conservative reading for heads formed from welded plate.
UG-27 is valid only while P ≤ 0.385·S·E — beyond that the membrane thin-wall assumption breaks and Appendix 1 thick-shell formulas take over. The engine also enforces UG-16 minimum thickness (1.5 mm + CA excluding lining) and flags CA fractions above 40 % of required thickness: at that point the vessel is being "designed by corrosion allowance" and service life becomes the real design case.
MAWP is back-calculated from the SELECTED plate in new condition (CA deducted), because that is what goes on the nameplate. The 1.3× hydrotest factor (UG-99, post-1999 code) applies the stress ratio so hot-design vessels are not over-stressed in the cold test bay; the test pressure must not exceed the limit that yields the vessel visibly.
Fabricators add mill undertolerance (plate can be 0.3 mm under nominal), forming thinning on heads (10–15 % in the knuckle), and round to stocked plate. The engine flags none of these silently — it selects standard plate, but head-forming thinning must be specified on the drawing as "minimum after forming".
No. External pressure is buckling, governed by UG-28 geometry/stiffening charts — completely different physics. A vessel rated 10 bar internal may fail at 0.5 bar external; if vacuum is possible (steam-out, blocked-in drain), run the external-pressure case separately.
Every opening removes load-bearing area and must be reinforced per UG-36/37 — the area-replacement rule. Thin walls from this calculator are the STARTING point: nozzle reinforcement routinely forces local pads or thicker shell courses around large openings.
The preset is included for feasibility comparison (EN 13445 practice uses comparable allowables). A stamped ASME vessel requires code-listed materials with the exact II-D allowable at design temperature — the custom-S field exists for that.
