Series of Flange Leakage
Calculation
Kellogg's Pressure Equivalent
Method
PIPING DEPARMENT
PIPE STRESS & FLEXIBILITY
BERCA ENGINEERING INTERNATIONAL
By Ardian Roekettino
Sr. Piping Engineer
Introduction
What is flange? flanges are critical components in piping systems,
providing connections between pipe sections, valves, and
equipment. Ensuring a leak-free bolted flange joint is essential for
maintaining system integrity and safety.
One of the methodologies used to evaluate flange performance
under external loads is the Kellogg's Pressure Equivalent Method.
This method converts external forces and moments into an
equivalent pressure that can be compared against allowable limits.
Introduction
Why do we need to perform Flange Leakage
calculation?
The design of flanges (ASME B 16.5) does not take into
account the bending moment in the pipe
Additional flexibility is to be provided when a flange
joint is located near a point of high bending moment
Leakage checking is required
Basics of Flange Leakage
Flange leakage
occurs due to
multiple factors,
including:
Gasket failure
(improper selection,
degradation, or
seating stress issues)
Bolt relaxation due
to temperature
changes or improper
tightening
Pipe misalignment
causing excessive
bending moments
Overpressure or
vacuum conditions
beyond design limits
Thermal expansion
and dynamic loads
Flange Leakage Concern

The possibility of flange leakage occurring well before the
failure of the pipe or the flange is a major concern of piping
engineers when the allowable piping expansion stress-range
runs well over the yield strength of the piping material. Even
with the structural integrity of the flange intact, the system is
still not functional if the flange tightness is not maintained.

Flange leakage is a very complex problem involving many
factors. Inadequate pressure rating, poor gasket selection,
insufficient bolt loading, temperature gradient, bolt stress
relaxation, piping forces and moments, and so forth, can all
cause leakage at a flange. In this paper, we will limit us to
the effects of piping forces and moments.
Kellogg's Pressure
Equivalent Method

Developed by M.W. Kellogg, this
method simplifies the analysis of
flange joints under external
loads by transforming bending
moments into an equivalent
internal pressure. The basic
equation is:
Kellogg's Pressure
Equivalent Method

The approach assumes that the
action of the moment and force is
equivalent to the action of the
pressure, which produces a gasket
stress that is the same as the gasket
stress produced by the force and the
moment. The equivalence criteria is
SF + SM = SP, where SF represent the
gasket stress due to force, SM the
maximum gasket stress due to
moment, and SP the gasket stress
due to equivalent pressure. Hence
the equivalence relation becomes:
Understanding The Kellog’s Pressure Equivalent
Method
The gasket
stress due
to force

The max.
gasket
stress due
to
moment
the gasket stress due
to equivalent
pressure
The Kellogg Equivalent Pressure Method is a technique for analyzing gasket
loads in bolted flange joints, particularly for evaluating the effects of internal
pressure and external loads on gasket integrity
Understanding The
Kellogg's Pressure
Equivalent Method
 Gasket Load Calculation
 The
gasket load is expressed in
terms of force per unit length of
the gasket circumference.
 The reaction
at the free-to-rotate
edge is analyzed using circular plate
theory.
Understanding The
Kellogg's Pressure
Equivalent Method
 Gasket Load Equations
Understanding The
Kellogg's Pressure
Equivalent Method
 Bending
 Effect of Bending
 The
Moments
moments change
gasket load distribution.
the
edge reaction is evaluated
using Timoshenko’s circular plate
theory.
 The minimum and maximum gasket
loads under bending moments are
determined.
Understanding The
Kellogg's Pressure
Equivalent Method
 Equivalent Pressure
Concept
Understanding The
Kellogg's Pressure
Equivalent Method
 Gasket Load Limits and
Tightness Condition
Understanding The
Kellogg's Pressure
Equivalent Method
 Conclusion

The Kellogg Equivalent Pressure Method provides
a structured approach to estimating gasket loads
in bolted flange joints.

By converting external forces and moments into
an equivalent pressure, this method simplifies
the assessment of flange tightness and ensures
reliable sealing.

The approach is conservative and ensures that
flange design accounts for both internal
pressure and mechanical loads, helping
engineers prevent flange leakage and maintain
joint integrity in pressurized systems.
Application of
Kellogg's Method

The Kellogg method is widely
used for:
•
Verifying flange integrity under
external piping loads
•
Ensuring compliance with ASME
B31.3 and ASME Section VIII
standards
•
Avoiding
excessive
flange
rotation and gasket crushing
•
Assessing flange behavior in
offshore
and
high-pressure
piping systems
Advantages and Limitations of Kellogg's Method
Advantages:
Simplifies complex
loading conditions
into a single
equivalent
pressure.
Provides a quick
check for potential
flange failures.
Applicable to
various flange
types and pressure
classes.
Limitations:
Does not consider
nonlinear gasket
behavior explicitly.
Thermal and
dynamic effects
require additional
considerations.
Conservative in
certain applications
leading to
overdesign.
Manual Calculation of Kellog’s Method
Caesar II Calculation of Kellog’s Method
Caesar II Calculation of Kellog’s Method
Select the flange analysis temperature & check the result
Reference
1.
Kellogg, M.W. (1956). Design of Piping Systems.
2.
ASME B31.3 (2022). Process Piping Code.
3.
ASME PCC-1 (2022). Pressure Boundary Bolted Flange Joint Assembly.
4.
Brown, W. (2013). "Improved Analysis of External Loads on Flanged Joints." ASME PVP
Conference.
5.
Rodabaugh, E.C. & Moore, S.E. (1976). Evaluation of the Bolting and Flanges of ANSI
B16.5 Flanged Joints.
6.
Waters, E.O. et al. (1937). "Formulas for Stresses in Bolted Flanged Connections." ASME
Transactions.
7.
Paulin Research Group (2003). AxiPRO 2.0 Program Manual.
8.
BS EN 1591-1 (2013). Flanges and Their Joints – Design Rules.
9.
Schneider, R.A. (2024). "A Numerical Comparison of Different Methods for Evaluating
Pipe Flanges Under External Loads." Journal of Pressure Vessel Technology.
10. ASME Section VIII, Division 1 & 2 (2021). Rules for Construction of Pressure Vessels.