Effects of Analysis Method, Bolt Pre-Stress, and Cover Plate

Thickness on the Behavior of Bolted Flanges of Different

SizesFinal Presentation

Chris WowkMANE 6970

Master’s Project

The objective of this project was to evaluate the behavior of flat faced cover plate/flange joints using:◦ Radial Beam Theory (Analytic Solution)◦ Solid Element Finite Element Models◦ Shell/Beam Element Finite Element Models

The effect of the following design variables on joint behavior were also investigated:◦ Bolt pre-stress◦ Cover plate thickness◦ Nominal pipe size

Objective

ASME B16.5 standard flange/cover plate sizes were used

Typical flange (steel) and bolting (CRES) materials were used

Cases Analyzed

Analytical Solution Analytical solution

developed by considering the annular portion of the flange and cover plate as a collection of radial beams

Moment diagram allowed for expressions for flange rotations and deflections be determined through integration

Separation of the joint was then calculated

FEA Analyses

Solid Element Model Shell/Beam Element Model

Cases RunNPS Size

Cover Thickness

Bolt Pre-Stress 0Pressure

Load25% Yield

80% Yield

0Pressure

Load25% Yield

80% Yield

0Pressure

Load25% Yield

80% Yield

0Pressure

Load25% Yield

80% Yield

Radial Beam Theory

Solid Element FEA

Shell Element FEA

Radial Beam Theory

Appendix Y Equations

Solid Element FEA

Shell Element FEA

Radial Beam Theory

Appendix Y Equations

Solid Element FEA

Shell Element FEA

Radial Beam Theory

Solid Element FEA

Shell Element FEA

Joint Separation Along Length

Radial Location of Contact

Stress In Center of Cover

Maximum Joint Separation

AnalysisMethod

t1 0.5*t1 2*t1

4"

t2

16"

Differences exist in the joint behaviors predicted by the different analysis types ◦ Shell/beam FEA predicted joint separations typically smaller than

other methods Bolt modeling method is the expected causes

◦ RBT not able to predict complete separation between cover plate and flange at zero pre-stress

General conclusions that the different analysis types were in agreement on:◦ Joint separation decreases as bolt pre-stress and/or cover plate

thickness increase◦ Radial location of contact moves closer to the bolt circle as bolt

pre-stress increases Results from smaller pipe size could not be scaled for larger

pipe size (non-linear)

Joint Behavior Results

Radial and tangential stresses in the center of the cover plate generally decreased as bolt pre-stress and/or thickness increases

Values differed between the analysis types FEA results showed increases in stress at

80% yield pre-stress◦ Cause is unknown – potential element distortion

issue

Cover Plate Stress Results

Analysis type matters in evaluating flat faced bolted flange joints

High bolt pre-stress is required to limit separation of flange components and reduce leak potential

Separation can also be reduced by increasing cover plate thickness

Be wary of how you model bolts in FEA

Overall Conclusions

ASME Boiler and Pressure Vessel Code, Section VIII – Rules for Construction of Pressure Vessels, 2013 Edition, Appendix Y.

Galai, H and Bouzid, A.H, “Analytical Modeling of Flat Face Flanges with Metal-to-Metal Contact Beyond the Bolt Circle,” Journal of Pressure Vessel Technology, Vol 132, 2010.

Schneider, R.W, “Flat Face Flanges with Metal-to-Metal Contact Beyond the Bolt Circle,” Transactions of the ASME, Vol 90, 1968, pgs 82-88.

Waters, E.O and Schneider, R.W, “Axisymmetric, Nonidentical, Flat Face Flanges with Metal-to-Metal Contact Beyond the Bolt Circle,” Journal of Engineering for Industry, Vol 91, 1969, pgs 615-622.

References