What is a flange leakage check?

A flange leakage check verifies that a bolted flange joint has sufficient bolt load to seat the gasket and maintain a seal under operating pressure. Per ASME VIII Appendix 2, the available bolt area must exceed the required bolt area for both seating (Wm2) and operating (Wm1) conditions. The gasket must achieve minimum seating stress (y factor) and maintain compression exceeding m times the operating pressure.

What is the ASME PCC-1 standard?

ASME PCC-1 (Guidelines for Pressure Boundary Bolted Flange Joint Assembly) provides procedures for assembling bolted flange joints to achieve leak-free performance. It covers bolt torque targets, tightening sequences (star pattern), gasket selection, and joint assembly best practices. PCC-1 is referenced by refineries and pipeline operators as the standard for flange assembly.

What are gasket m and y factors?

The m factor (maintenance factor) is the ratio of gasket stress to internal pressure required to maintain a seal during operation. The y factor (seating stress) is the minimum gasket stress in psi required to initially seat and conform the gasket to flange face irregularities. These values come from ASME VIII Table 2-5.1. For spiral wound gaskets, m=3.0 and y=10,000 psi. For ring joint gaskets, m=5.5 and y=18,000 psi.

How is bolt torque calculated for flanges?

Target bolt torque is calculated using T = K x D x F, where K is the nut factor (0.20 for unlubricated, 0.15 for lubricated), D is the bolt nominal diameter, and F is the target bolt load per bolt. The target bolt load is typically 40-50 ksi stress on the bolt root area for ASTM A193 B7 bolts. ASME PCC-1 provides specific torque tables by bolt size and lubrication condition.

Flange Leakage Check Calculator | ASME PCC-1 Bolted Joint Analysis

Flange Specification

Flange Class

Flange Size (NPS)

Flange Type

Gasket Selection

Gasket Type

Gasket Material

Gasket m Factor

Auto-filled from gasket type (ASME VIII Table 2-5.1)

Gasket y Factor (Seating Stress)

psi

Design Conditions

Design Pressure

psig

Design Temperature

°F

External Moment (optional)

ft-lbs

External Axial Force (optional)

lbs

Bolt Specification

Bolt Material (ASTM A193)

Bolt Lubrication

Note: Bolt count, diameter, and gasket dimensions are auto-populated from ASME B16.5 flange standards based on selected class and size.

Understanding Flange Leakage Checks

ASME VIII Appendix 2 Method
The code method checks two bolt load conditions: (1) gasket seating at ambient with no pressure, requiring bolt stress to achieve minimum gasket seating stress y; and (2) operating condition where bolt load must resist hydrostatic end force plus maintain gasket compression at m × P.

Why Flanges Leak
Common causes: insufficient bolt torque, uneven bolt loading, incorrect gasket selection, thermal cycling, external bending moments, corrosion of flange faces, and exceeding pressure-temperature ratings. ASME PCC-1 addresses most assembly-related causes.

Gasket Factors (ASME VIII Table 2-5.1):
Spiral wound (m=3.0, y=10,000 psi) | Ring joint iron (m=5.5, y=18,000 psi) | Flat graphite (m=2.0, y=3,700 psi) | Kammprofile (m=3.0, y=10,000 psi)

Learn the Theory

Understand bolted flange joint theory, ASME PCC-1 assembly procedures, gasket selection, and torquing best practices

Read Engineering Guide →

Results

Leakage Assessment

Required Bolt Area (Am) -

Available Bolt Area (Ab) -

Bolt Area Margin -

Operating Bolt Load (Wm1) -

Seating Bolt Load (Wm2) -

Hydrostatic End Force (H) -

Gasket Seating Stress -

Gasket Operating Stress -

Target Bolt Torque -

Bolt Stress at Assembly -

Bolt Count × Diameter -

Formulas

Am = max(Wm1/Sa, Wm2/Sa)

Am = Required bolt area (in²)

Wm1 = H + Hp (operating bolt load, lbs)

Wm2 = π × b × G × y (seating bolt load, lbs)

H = π/4 × G² × P (hydrostatic end force)

Hp = 2 × b × π × G × m × P

Sa = Bolt allowable stress at temperature

T = K × D × F (bolt torque, ft-lbs)

Standards & References

ASME PCC-1
Guidelines for Pressure Boundary Bolted Flange Joint Assembly
ASME B16.5
Pipe Flanges and Flanged Fittings (NPS 1/2 - 24)
ASME VIII Div.1, Appendix 2
Rules for Bolted Flange Connections
ASME VIII Table 2-5.1
Gasket Materials and Contact Facings (m and y factors)
ASME B16.20
Metallic Gaskets for Pipe Flanges

Engineering Notes

Bolt load: ASME VIII requires Am ≤ Ab for both seating and operating conditions
Gasket seating: Gasket stress must exceed y factor to achieve initial seal
Operating seal: Residual gasket stress must exceed m × P during operation
Assembly torque: PCC-1 recommends controlled torquing with star pattern, minimum 3 passes
B7 bolts: Typical assembly stress 40-50 ksi; yield = 105 ksi at ambient
Temperature: Bolt allowable stress decreases with temperature per ASME II Part D

Quick Reference — Gasket m & y Factors

Spiral Wound (SS/Graphite): m = 3.0, y = 10,000 psi
Ring Joint (Soft Iron): m = 5.5, y = 18,000 psi
Flat Sheet (Graphite): m = 2.0, y = 3,700 psi
Kammprofile: m = 3.0, y = 10,000 psi
PTFE Envelope: m = 2.0, y = 1,100 psi

Flange Leakage Check Calculator

Flange Specification

Gasket Selection

Design Conditions

Bolt Specification

Understanding Flange Leakage Checks

Learn the Theory

Results

Formulas

Standards & References

Engineering Notes

Quick Reference — Gasket m & y Factors

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