Flange Comparison Tool
Compare flanges across standards or pressure classes to see whether their bolt holes line up — shown in the 45° installed orientation. Get a bolt diameter recommendation, a machining allowance, and an integrity warning if the machining gets too aggressive. Toggle a second pair (C vs D) to compare four flanges at once.
Pair 1 — A vs B
Flange A (actual)
Flange B (proposed)
Pair 2 — C vs D
Turn on to add a second comparison (C vs D) — useful when weighing two replacement options against the same installed flange.
Bolt Circle Overlay
Comparison
Bolt holes do NOT line up
PCD differs by 14.0 mm — holes won't align.
Different number of bolt holes (4 vs 8).
M16
Sized to the smaller hole (18 mm) so the bolt passes through both flanges.
Machining won't help
Different bolt counts can't be realigned by oversizing — the flanges must be re-drilled or a transition flange/spacer used.
How It Works
1. Pick each flange by nominal size, standard and pressure class / table. A is the installed (actual) flange; B is the candidate (proposed) replacement.
2. 45° installed orientation — the overlay draws bolt holes at 45°, the way a flange actually hangs in the field (a 4-bolt flange forms a diamond, not a cross).
3. Mating check — flanges mate when their Pitch Circle Diameter and number of bolt holes match (within normal rounding tolerance).
4. Bolt recommendation — the bolt must physically pass through both flanges, so the recommended diameter is sized to the smaller of the two hole diameters.
5. Bolt that fits as-is — when PCDs differ but hole counts match, the tool estimates the largest bolt that still drops through the overlap of the two misaligned holes.
6. Machining option & integrity warning — to use the standard bolt despite a PCD mismatch, the tool calculates how much the smaller-PCD flange's holes must be enlarged, and flags it as Acceptable / Caution / Severe / Do-not-machine based on the enlargement as a percentage of the original hole. Beyond ~50% the ligament between bolts is destroyed.
7. Two pairs (A vs B and C vs D) — toggle the second pair to compare four flanges at once, e.g. two replacement options against two installed flanges.
8. Zoom & pan — scroll to zoom, drag to pan the overlay. Dimension lines mark the outside diameter, pitch circle diameter and hole sizes for each flange.
Important disclaimer
A matching PCD and hole count confirms the bolt pattern aligns — it does not confirm pressure rating, gasket face type, or flange facing compatibility. The machining integrity warning is a guide only; always have a competent person re-verify the flange's pressure rating and ligament against the governing standard after any modification.