⚠️ Guide préliminaire seulement. Vérifier avec un ingénieur qualifié avant utilisation. ELASFOR décline toute responsabilité. ⚠️ Preliminary guidance only. Verify with a qualified engineer before production use. ELASFOR assumes no liability.
Click a pressure class to view Ring and Full Face gasket dimensions per ASME B16.21
150#
ASME B16.5 / B16.47
~285 psi @ 100°F
300#
ASME B16.5 / B16.47
~740 psi @ 100°F
600#
ASME B16.5 / B16.47
~1,480 psi @ 100°F
900#
ASME B16.5 / B16.47
~2,220 psi @ 100°F
1500#
ASME B16.5
~3,705 psi @ 100°F
2500#
ASME B16.5
~6,170 psi @ 100°F
Units:
⚠️ Note: Flange classes over 300# have pressure ratings that may exceed the rating of most non-metallic gasketing products. Contact your gasket supplier for high-pressure applications.
Large Bore Flanges (ASME B16.47)
Bolt Torque Values
Source: Durlon® (Triangle Fluid Controls / Gasket Resources Inc.) — ASME B16.5-2017 MAWP basis. Sheet gasket: ASME B16.21 Ring Gasket. Spiral Wound: ASME B16.20 inner/outer ring (DRI) style. REV. 2021/11. Assumptions: A193 Grade B7 studs · A194 Grade 2H heavy hex nuts · Two hardened steel flat washers per nut · Nuts, bolts and washers lubricated (do not lubricate gasket) · Calibrated torque wrench · Minimum 3 even increments · Counter-clockwise verification pass after final torque. Note: Values are for raised face metallic flanges. For lined or non-metallic flanges consult the flange manufacturer. Not compensated for elevated or fluctuating temperatures.
How these values are calculated (Garlock method): ① Contact Area = π(OD² − ID²) / 4 — raised face O.D. minus gasket I.D. ② Max Gasket Stress = (N bolts × compressive force/bolt) ÷ Contact Area ③ Min Torque = (Min gasket stress ÷ Max gasket stress) × Max torque at 60 ksi bolt stress ④ Preferred Torque = Full bolt torque at 60 ksi, unless that would exceed 15,000 psi on gasket — in which case: (15,000 ÷ Max gasket stress) × Max bolt torque. Minimum recommended gasket stress = 2,500 psi (Class 150) / 3,800 psi (Class 300).
Sheet Gasket Torque Reference (Durlon)
Durlon® ASME B16.21 ring gasket — compressed sheet material. A193-B7/B16 studs, A194-2H nuts, never-seize lubricant (k=0.17). Min = 4,800 psi gasket stress · Optimal = 7,000–12,000 psi · Max = 15,000 psi. Rounded to nearest 5 ft·lbs.
Spiral Wound Gasket Torque Reference
Durlon® ASME B16.20 inner/outer ring (DRI) spiral wound gasket. A193-B7/B16 studs, A194-2H nuts, never-seize lubricant (k=0.17). Min = 12,500 psi gasket stress · Optimal = 25,000 psi · Max = 40,000 psi. All values rounded to nearest 5 ft·lbs.
Surface Finish Requirements (Ra)
Gasket Type
Finish Type
µ-inch
µm
Compressed Non-Asbestos (CNA)
Stock / Serrated
125 - 500
3.2 - 12.5
PTFE (Filled & Expanded)
Stock / Serrated
125 - 250
3.2 - 6.3
Flexible Graphite
Stock / Serrated
125 - 250
3.2 - 6.3
Spiral Wound Gaskets
Stock / Serrated
125 - 250
3.2 - 6.3
Kammprofile / CFG
Stock / Serrated
125 - 250
3.2 - 6.3
Metallic Serrated Gaskets
Smooth
63 max
1.6 max
Ring Type Joint (RTJ)
Machined RTJ Groove
63 max
1.6 max
Gasket Seating Stress Ranges
Gasket Type/Style
Min. Stress
Max. Stress
psi
bar
psi
bar
Graphite Sheet
1,000 - 2,000
69 - 138
10,000 - 24,000
690 - 1,655
Compressed Non-Asbestos
2,500 - 4,000
172 - 276
15,000
1,034
PTFE (Filled)
1,500 - 2,500
103 - 172
10,000 - 15,000
690 - 1,034
Expanded PTFE (ePTFE)
1,000 - 1,500
69 - 103
8,000 - 10,000
552 - 690
Kammprofile
2,500 - 4,000
172 - 276
35,000 - 40,000
2,413 - 2,758
Corrugated Graphite (CFG)
4,000 - 5,000
276 - 345
30,000
2,068
Spiral Wound (Standard)
7,500 - 10,000
517 - 690
30,000 - 40,000
2,068 - 2,758
Spiral Wound (Low Stress)
5,800
379
30,000 - 35,000
2,068 - 2,413
Ring Type Joint (RTJ)
—
—
35,000 - 40,000
2,413 - 2,758
Common Bolt Materials
ASTM
EN Equivalent
Material
Yield Strength
Application
A193 B7
1.7225 (42CrMo4)
Chrome-Moly Steel
105 ksi min
Standard high-temp service
A193 B16
1.7711 (40CrMoV4-6)
Chrome-Moly-Vanadium
105 ksi min
High-temp, higher strength
A193 B8 Cl.1
1.4301 (304 SS)
18-8 Stainless
30 ksi min
Corrosion resistance
A193 B8M Cl.1
1.4401 (316 SS)
18-8 Mo Stainless
30 ksi min
Enhanced corrosion
A320 L7
—
Chrome-Moly
105 ksi min
Low temperature service
Gasket Thickness Recommendations
1/16" (1.5mm): Preferred for flanges up to 8" NPS — less creep relaxation
1/8" (3mm): Standard for 10" NPS and larger — better conformability
Thinner is better: Within limits, thinner gaskets have less creep and better torque retention
Surface condition: Damaged or pitted flanges may require thicker gaskets
Never stack multiple gaskets — use correct single thickness
Gasket Installation Procedure (per ASME PCC-1)
1
Safety & Preparation
Ensure system is at ambient temperature and fully depressurized. Follow local safety rules and lockout/tagout procedures.
2
Inspect & Clean
Visually examine flanges, bolts, nuts and washers. Clean all surfaces. Replace defective components. Check flange surface finish meets requirements for gasket type.
3
Align Flanges
Flanges must be parallel within 1mm per 100mm of flange OD. Bolt holes should align without forcing bolts. Do not use gaskets to correct misalignment.
4
Install Gasket
NEVER reuse gaskets or use multiple gaskets. Center gasket on flange. Do not use grease to hold gasket in place.
5
Hand Tighten
Install all bolts and hand tighten nuts. Snug with hand wrench (⅛ to ¼ turn). Number bolts in cross-pattern sequence.
6
Torque Rounds (Cross Pattern)
Round 1: 30% of target torque Round 2: 60% of target torque Round 3: 100% of target torque Check flange gap at 90° intervals between rounds.
7
Rotational Round
Using clockwise sequence starting at bolt #1, tighten at 100% target torque. Continue for at least two complete rounds until no further nut rotation occurs.
8
Re-Torque (Critical!)
Re-torque after 4-24 hours. Up to 10% preload loss occurs in first 24 hours due to bolt relaxation and gasket creep. Especially important for PTFE gaskets.
Bolt Tightening Patterns
4-Bolt
8-Bolt
12-Bolt
Common Failure Causes
🔩 Under-Torque
Insufficient gasket stress
Poor initial seal
Rapid creep relaxation
Vibration loosening
⚡ Over-Torque
Exceeding max gasket stress
Soft gaskets: max 15,000 psi
Metallic: max 30,000 psi
Crushing damages gasket
↔️ Misalignment
Uneven bolt load
Localized stress
Point loading failure
Gasket blowout
♻️ Gasket Reuse
Never reuse gaskets
Never stack gaskets
Exception: some kammprofile
Always use new gasket
Reference Standards
ASME PCC-1: Guidelines for Pressure Boundary Bolted Flange Joint Assembly
EN 1591-4: Qualification of personnel competency in assembly of bolted connections
ASME B16.5: Pipe Flanges and Flanged Fittings (NPS 1/2 through NPS 24)
ASME B16.47: Large Diameter Steel Flanges (NPS 26 through NPS 60)
ASME B16.20: Metallic Gaskets for Pipe Flanges
ASME B16.21: Nonmetallic Flat Gaskets for Pipe Flanges