FitterMaster Flange bolt tightening sequence: star pattern and torque in three passes
Tighten a flange in a star (cross) pattern, jumping across the flange each time, in passes of about 30%, 60% and 100% of the final torque. An 8-bolt flange goes 1 → 5 → 3 → 7 → 2 → 6 → 4 → 8. FitterMaster's Flange & Bolt screen gives the order, the stud count and size, the bolt circle and the three torque figures for a B16.5 flange.
Why does the tightening order matter?
Pulling one side of a flange tight first cocks it and crushes the gasket unevenly, and that is how joints leak on test. Going round in a star pattern, in several passes, brings the faces together evenly. Skipping this sequence is a common way for a joint to fail hydro, so we built the sequence into the app rather than trust anyone to remember it at 6am.
Star pattern by bolt count
| Bolts | Order |
|---|---|
| 4 | 1 → 3 → 2 → 4 |
| 8 | 1 → 5 → 3 → 7 → 2 → 6 → 4 → 8 |
| 12 | 1 → 7 → 4 → 10 → 2 → 8 → 5 → 11 → 3 → 9 → 6 → 12 |
The app also has the patterns for 16, 20 and 24 bolts and draws them on a numbered flange diagram.
How do you use Flange & Bolt?
- Open Flange & Bolt under Reference (Pro).
- Under Flange, pick the Size (NPS 1/2 to 24) and the Class: 150, 300 or 600.
- Read Bolt-Up: Bolts (count × stud diameter) and Bolt Circle.
- Read Torque — 3 passes for the 30%, 60% and 100% figures.
- Follow Star Sequence: the diagram numbers each bolt and the line under it, starting with Order:, lists the sequence. Repeat it on every pass.
- Tap Copy or Share on the bolt-up card to send the details.
The screen remembers the last size and class you used.
Worked examples, Class 150
| Flange | Bolts | Bolt Circle | 30% pass | 60% pass | 100% pass |
|---|---|---|---|---|---|
| 2" Class 150 | 4 × 5/8" | 4.75" | 32 ft-lb | 63 ft-lb | 105 ft-lb |
| 6" Class 150 | 8 × 3/4" | 9.50" | 56 ft-lb | 112 ft-lb | 186 ft-lb |
| 12" Class 150 | 12 × 7/8" | 17.00" | 90 ft-lb | 180 ft-lb | 301 ft-lb |
In millimetre mode torque is in N·m: the 6" Class 150 passes read 76, 152 and 253 N·m.
How is the torque calculated?
The app uses the short-form torque formula T = K × D × F. K is 0.17 for lubricated studs, D is the stud diameter and F is the target preload: 50% of the 105,000 psi yield of A193 B7, times the stud's tensile stress area. For a 3/4" stud that is 0.5 × 105,000 × 0.334 in² = 17,535 lbf, and 0.17 × 0.75 × 17,535 ÷ 12 = 186 ft-lb.
Common mistakes
- Going round the flange in a circle instead of across it.
- Jumping straight to full torque in one pass.
- Using the lubricated figure on dry studs, or a different grade of stud.
- Skipping a final check pass round in order at 100%.
Questions and answers
What is the tightening sequence for an 8 bolt flange?
Which flanges does it cover?
Can I change the stud grade or nut factor?
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