Bolted Flange Connection Under Preload and Internal Pressure

A bolted flange connection was assessed to evaluate its structural performance under combined loading conditions, including bolt preload and internal pressure. Such connections are widely used in piping systems and pressure-containing assemblies, where maintaining joint integrity and preventing leakage is critical.

Finite element analysis was conducted to investigate stress distribution across the flange, bolts, and sealing interface, ensuring the design met performance and reliability requirements.

Challenge

Bolted flange connections are inherently complex due to the interaction between multiple components, including bolts, flanges, and gasket interfaces. Uneven load distribution, insufficient preload, or localised stress concentrations can lead to joint separation, leakage, or long-term fatigue failure.

The objectives of the analysis were to:

• Evaluate stress distribution within the flange and bolts

• Assess the effect of bolt preload on joint performance

• Identify potential leakage paths at the sealing interface

• Ensure the connection maintained integrity under internal pressure

Solution

A detailed finite element model of the bolted flange assembly was developed, incorporating bolt preload, contact interactions, and internal pressure loading.

The analysis:

• Simulated bolt tightening to establish realistic preload conditions

• Applied internal pressure to replicate service operation

• Evaluated equivalent (von Mises) stress across the flanges and bolts

• Assessed contact pressure distribution at the sealing interface

The results highlighted non-uniform stress distribution around the bolt circle, with elevated stresses occurring near bolt holes and flange transitions. Contact pressure at the gasket interface was also evaluated to ensure adequate sealing performance.

Outcome

The analysis provided a comprehensive understanding of the mechanical behaviour of the bolted connection under realistic loading conditions.

Key outcomes included:

• Identification of peak stress regions around bolt holes and flange faces

• Verification of sufficient bolt preload to maintain joint integrity

• Assessment of sealing performance through contact pressure distribution

• Insight into load transfer between bolts and flange components

Recommendations included optimising bolt preload levels, refining flange geometry, and ensuring uniform load distribution to enhance sealing reliability and reduce localised stress concentrations.

Testimonial

“The analysis gave us confidence that the flange connection would perform reliably under pressure. The insight into bolt preload and sealing behaviour was particularly valuable in refining the design.”​

— Mechanical Engineer, Piping Systems