Piping design engine for process and piping engineers: pressure design per B31.3 §304.1.2 — t = P·D/(2(S·E·W + P·Y)) — with joint factors, Y-coefficient, corrosion allowance, 12.5 % mill undertolerance screening, automatic NPS/schedule selection from the dimensional database, and MAWP back-calculation on the selected schedule. Allowable stress presets for A106/A53/TP304 with temperature derating. Every input with selectable universal units, every report with the full audit trail.
SectorCalc SC-034 sizes pipe wall per ASME B31.3 Process Piping §304.1: the straight-pipe internal-pressure equation with joint factor E, weld-strength factor W, coefficient Y, corrosion/threading allowance, and the 12.5 % mill-undertolerance screen that decides whether a schedule REALLY works — then back-calculates the MAWP of the selected schedule. Scope is pressure design of straight pipe only: flexibility (thermal stress), sustained/occasional loads, branch reinforcement and flanged joints are separate B31.3 chapters. Results are pre-design grade for licensed piping engineer review.
The equation uses OUTSIDE diameter, which is fixed per NPS — that is why schedules exist as discrete steps. Y places the design stress at the correct fibre of the wall (0.4 for ferritic puts it near mid-wall). Watch the P·Y term in the denominator: at high pressure it measurably softens the required wall, one of the code's quiet nonlinearities.
E penalizes the weld: seamless 1.00, ERW with spot RT 0.85, furnace butt 0.60. W enters only in the creep range, where weld metal creeps faster than parent — below ~450 °C it stays 1.0. Y is material-physics, not workmanship: ferritic 0.4, austenitic 0.5, nickel alloys 0.7 per Table 304.1.1.
Pipe mills can legally deliver 12.5 % under nominal wall — the schedule you buy is not the wall you get. This single factor kills more paper designs than any other: a 2″ SCH40 (3.91 mm) pipe really offers 3.42 mm. The engine screens every schedule with the 0.875 factor and picks the lightest passing one.
MAWP runs on the fully corroded, undertoleranced wall — the worst legal condition the line can ever see. Comparing MAWP-new and MAWP-corroded tells you the corrosion-life story of the line at a glance.
Pressure design of STRAIGHT pipe only. Not covered: B31.3 Chapter II flexibility (thermal expansion stress — usually the real design driver on hot lines), sustained-plus-occasional longitudinal stress, branch reinforcement per §304.3, flanges (B16.5 pressure-temperature tables), and Category M / high-purity / high-pressure (Chapter IX) rules. B31.1 power piping uses a slightly different equation form — do not mix.
Mill undertolerance. Check the numbers: 0.875 × SCH40 wall minus your corrosion allowance is below the required t. The code screens on what the mill can legally deliver, not the catalog number.
Yes — PTFE/rubber lining or cladding can justify c = 0 on the pressure design, but the lining integrity becomes a maintenance item and the code still requires external corrosion consideration. Document the basis in the line class specification.
Partially: the allowance c must include thread depth for threaded ends (ASME B1.20.1 thread height) — add it to the corrosion figure. Socket-weld and butt-weld ends need no such addition.
Design pressure must cover the relief valve set pressure plus accumulation per your line class. Occasional variations above design are governed by §302.2.4 with their own allowable multipliers — they do NOT relax the base wall sizing.
