Pressure Vessel Shell Calculator — ASME VIII UG-27 / UG-32
Industrial-grade vessel design calculator: cylindrical shell per UG-27, formed heads per UG-32, joint efficiency, corrosion allowance, plate selection, MAWP back-calculation, hydrostatic test per UG-99 and full audit trail.
Decision:Run the stated engineering model, review its assumptions and warnings, then make the release decision against the governing standard and verified source data.
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.
Cylindrical shell per UG-27
Circumferential: t = P·R / (S·E − 0.6·P)
Longitudinal: t = P·R / (2·S·E + 0.4·P)
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.
Formed heads per UG-32
2:1 elliptical: t = P·D / (2·S·E − 0.2·P)
Torispherical: t = P·L·M / (2·S·E − 0.2·P), M = (3 + √(L/r))/4
Hemispherical: t = P·L / (2·S·E − 0.2·P)
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.
Joint efficiency and radiography
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.
Validity window and thin-shell limits
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.
Frequently asked questions
Why is my calculated thickness thinner than the fabricator's quote?
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".
Can I use this for external pressure (vacuum)?
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.
What about nozzle reinforcement?
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.
Is P265GH / EN material acceptable in an ASME design?
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.
