Last updated: April 2026
Most spiral wound gasket leaks aren't a gasket failure — they're a bolt-up failure. The gasket is sized correctly, the filler is right for the service, and the flange is in good condition, but the assembler torqued it wrong: uneven sequence, wrong target, dry threads assumed lubricated, or no re-torque after thermal soak. ASME PCC-1 codifies the assembly practice that prevents this.
This guide is the practical version of ASME PCC-1 Appendix F applied specifically to spiral wound gaskets. It assumes you have a calibrated torque wrench, the right bolts and lubricant, and a flange in good condition.
Step 1 — Inspect the Flange Before You Touch the Gasket
- Surface finish — 125–250 µin Ra concentric serrations for spiral wound. Re-machine if galled or grooved deeper than 0.13 mm (0.005").
- Flatness — within ASME B16.5 tolerance. Wave or warp will not seal.
- Bolt holes & studs — clean threads, no thread damage. Replace galled studs; do not re-use one-time-use bolts.
- Bolt-hole alignment — flanges must align without forcing. If you can't slip the studs through by hand, the pipe stress will eat your gasket preload.
Step 2 — Check the Gasket and Set It Properly
- Verify the gasket matches the flange class, OD, ID, and standard (B16.20 stamped on the centring ring).
- Inspect the winding for damage, kinks, or filler delamination. Reject any gasket that doesn't sit flat on a benchtop.
- Place the gasket dry — no anti-stick spray, no grease on the sealing faces. Lubricant on the gasket reduces friction and lets the windings extrude.
- For raised-face flanges, the centring ring locates the gasket on the bolt circle. For ring-joint flanges, you need a different gasket entirely (RTJ).
Step 3 — Lubricate the Threads and Nut Faces (Not the Gasket)
Lubricant goes on thread flanks and the nut bearing face only. The lubricant choice changes the torque you need to deliver:
| Lubricant | Nut factor K | Notes |
|---|---|---|
| Dry / as-received | 0.20 | Inconsistent — only acceptable below Class 300 |
| General-purpose anti-seize (Cu, Ni, MoS₂ paste) | 0.16 | Default for refinery service |
| PTFE-based thread paste | 0.12 | Lower torque, lower scatter — premium choice |
| Hot-bolt waxes (e.g. nickel-graphite) | 0.13–0.15 | For high-temp service where standard pastes burn off |
Use the same lubricant on every bolt of the joint. Mixing lubricants is one of the most common causes of uneven preload across a flange.
Step 4 — Calculate the Target Torque
Target torque comes from target bolt preload, and bolt preload comes from gasket seating stress times gasket area. For a flexible-graphite-filled spiral wound gasket the target seating stress is 175 MPa (25,400 psi); for PTFE-filled it's about 140 MPa. Then:
F_bolt = (S_g × A_g) / N_bolts
T = K × F_bolt × d
where:
S_g = gasket target seating stress (Pa)
A_g = gasket effective contact area (m²)
N_bolts = number of bolts
K = nut factor (lubricant-dependent)
d = bolt nominal diameter (m)
F_bolt = target preload per bolt (N)
T = torque (N·m)Our bolt torque calculator handles this conversion for standard ASME B16.5 flange / bolt combinations — pick the class and bolt size, choose your lubricant, get the target torque.
Step 5 — Run the PCC-1 Tightening Sequence
ASME PCC-1 Appendix F specifies a four-pass cross-pattern bolt-up. Number every bolt 1 through N around the flange. Then:
- Pass 1 — finger-tight to ~30% target. Cross pattern (1, 7, 4, 10, 2, 8, 5, 11, 3, 9, 6, 12 on a 12-bolt flange). Establish even gasket compression.
- Pass 2 — to ~60% target. Same cross pattern. The gasket starts to seat properly here; the flange may visibly close.
- Pass 3 — to 100% target. Same cross pattern. Final seating stress reached.
- Pass 4 — rotational check at 100% target. Go around the flange clockwise (1, 2, 3, ... N) at full target. Any bolt that turns more than ~10° has lost preload from cross-pattern interaction; repeat until none turn.
For Class 600 and above, or any high-temperature service, add a fifth pass: hot re-torque after the joint has reached operating temperature and stabilised (typically 24 hours for steam systems). This recovers the preload lost to gasket creep and thermal stretch.
Step 6 — Verify and Document
- Record final torque and pass number per bolt — paper or electronic. Required for safety-critical service per PCC-1 Appendix O.
- Mark each bolt and nut with a paint-pen line after final torque. A broken paint line on a later inspection means the joint moved.
- Schedule a re-torque after 24 hours of steady operation for any joint above 200°C.
Common Mistakes That Cause Leaks
- Wrong lubricant assumed. Calculating with K = 0.16 then bolting up dry under-preloads by ~25%.
- Skipping Pass 1 / 2. Going straight to 100% target distorts the flange and over-crushes one side of the gasket.
- Re-using stretched studs. A2 / B7 / B8 studs that have been preloaded to 60%+ yield should not be re-used.
- No hot re-torque on Class 600+ steam service. Creep relaxation will drop preload below the operating m factor within a week.
- Lubricating the gasket itself. Reduces friction between filler and flange, lets the winding extrude.
Frequently Asked Questions
For a flexible-graphite-filled spiral wound gasket, target 175 MPa (25,400 psi) seating stress. For PTFE-filled, target 140 MPa (20,300 psi). For mica or ceramic fillers, refer to the manufacturer data sheet — typically 200 MPa or higher because the filler is less compressible.
A minimum of four passes: Pass 1 to 30% target torque in a cross pattern, Pass 2 to 60%, Pass 3 to 100%, then Pass 4 as a rotational check at 100% going clockwise around the flange. For Class 600+ or any service above 200°C, add a fifth hot re-torque after the joint has stabilised at operating temperature.
No. Lubricant on the spiral wound gasket sealing faces reduces friction between filler and flange and allows the winding to extrude under load — the joint loses its seal. Lubricant goes on the bolt thread flanks and the nut bearing face only. The same lubricant must be used on every bolt of the joint to keep preload uniform.
Any spiral wound gasket installed on a flange that will run above 200°C should be re-torqued after 24 hours of steady operation at temperature. The combination of gasket creep and bolt thermal stretch loses 10–20% of cold preload — the hot re-torque restores it before that loss drops the residual stress below the operating m factor.
For non-critical Class 150 / 300 joints, ASTM A193 B7 studs can typically be re-used twice if visually inspected and not visibly necked or stretched. For Class 600+ or safety-critical joints — and for any stud preloaded above 60% of yield — replace the studs every disassembly.
Related
- Bolt torque calculator
- What is a spiral wound gasket?
- Filler selection guide
- Spiral wound gaskets — full range
Sources
- ASME PCC-1 — Guidelines for Pressure Boundary Bolted Flange Joint Assembly (Appendix F: tightening sequence; Appendix J: target torque calculation)
- ASME B16.20 — Metallic Gaskets for Pipe Flanges
- ASME Section VIII Division 1, Appendix 2 — m and y factors