Flange Bolt Tightening Sequence Calculator (Star Pattern Chart + Pass Torques) — Sample Report

1 · Design inputs

The chart case from the thread: a 12-bolt flange, crew running impacts — no torque numbers anywhere on the job. The order is the whole product.

2 · Method

The sequence is built by two rules, applied to studs numbered clockwise from any starting bolt:

1. every bolt is followed immediately by its diametric opposite (bolt i → bolt i + N/2)

2. consecutive pairs rotate quadrants — the pair order is the same crossing applied to the half-count, recursively

For 4, 8, 12, 16, 24 and 32 bolts this reproduces, digit for digit, the legacy star charts published on gasket manufacturers' torque cards (the pattern ASME PCC-1's legacy tightening guidance describes). Crossing seats the gasket flat and keeps the flanges parallel; the quadrant rotation stops compression from walking around the joint one side at a time.

schedule: snug → 30% → 70% → 100% (cross pattern each pass) → final pass at 100%, circular

The percentages are editable (up to six cross passes); the final circular pass is always appended because it is the anti-leak pass: it catches the preload lost to elastic interaction during every cross pass. With a target torque entered, each pass row becomes a wrench setting, rounded to a tenth.

3 · Calculation

1. Pick any stud, call it bolt 1, and number the rest clockwise — the chart draws bolt 1 at 12 o'clock.
2. Cross the flange: bolt 7 is diametrically opposite, so it is tightened second. Every bolt in the order is followed by its opposite — that is what pulls the flanges up parallel instead of cocking them.
3. Rotate a quarter turn for the next pair: 4 and 10. Then 2–8, 5–11, 3–9, 6–12 — consecutive pairs keep rotating quadrants so gasket compression walks around the joint evenly.
4. Full order: 1 → 7 → 4 → 10 → 2 → 8 → 5 → 11 → 3 → 9 → 6 → 12 — digit for digit the 12-bolt chart on every gasket manufacturer's torque card.
5. Run that order at snug first and check the flange gap is even all around; run it again at each pass stage even without a wrench — the bolts hit early in a pass relax as their neighbours come up; finish around the clock 1, 2, 3… until nothing moves.

4 · Results COMPUTED

5 · Verification statement

The result values above are locked as fixture bolt-sequence.json, case “12-bolt flange, sequence only -> the universal published cross order”, tolerance 1e-9, in the calc-core continuous verification gate (see https://pipingtoolset.com/trust/validation.html). Allowable-stress and factor data are user-supplied inputs; citations: ASME PCC-1 — Guidelines for Pressure Boundary Bolted Flange Joint Assembly (context for the legacy cross pattern and multi-pass practice; no PCC-1 table values are embedded). · Gasket manufacturers' bolt-torque and assembly cards — the published star charts the 4–32 bolt sequences reproduce digit for digit. · ASME B16.5-2025 — flange drillings are multiples of four bolts (the basis of the count check).