Hinged Expansion Joint: Angular Movement in a Single Plane

In pipelines with large thermal expansion, controlling the direction and size of movement is the most effective way to reduce loads on anchors and connected equipment. A hinged expansion joint is a metal bellows expansion joint fitted with hinge hardware that permits angular rotation in one plane only.

This article explains how hinged expansion joints work, why they are usually installed as two- or three-hinge systems, and what to consider when selecting them.

How Does a Hinged Expansion Joint Work?

A hinged expansion joint consists of a single metal bellows. Hinge plates are welded to the end fittings on each side of the bellows and connected by a pair of hinge pins. Because the pins form a single axis, the joint can only rotate about that axis, i.e. angularly in one plane.

The hinge plates and pins are sized to carry the pressure thrust that internal pressure creates on the bellows. Hinged joints are therefore restrained expansion joints: the pressure thrust is not transferred to the main anchors. This is why the hinges and pins must be strong enough to carry pressure loads and external forces safely.

Why Two- or Three-Hinge Systems?

A single hinged joint cannot absorb axial or lateral movement; it only rotates. To accommodate pipeline movement, several hinged joints are normally used together:

• Two-hinge system: two hinged joints separated by an intermediate pipe absorb lateral offset in one plane.
• Three-hinge system: used on L- or Z-shaped pipe runs to absorb large thermal expansion of long pipe legs in a single plane.

In these systems the joints must be oriented to the plane of movement, with all hinge-pin axes perpendicular to that plane.

Applications

• Absorbing large thermal expansion of long pipelines in a single plane
• L- and Z-bends in steam, high-temperature water and hot process lines
• Lines where main anchors cannot carry large pressure thrust
• Changes of direction in tight spaces

Benefits

• Controlled movement: movement occurs only in the intended plane, so the pipeline behaves predictably.
• Carries pressure thrust: loads on main anchors are reduced, allowing lighter anchoring.
• Flexible layout: two- and three-hinge systems adapt to different routes and movements.
• Robust design: a strong hinge mechanism provides a long service life.

Frequently Asked Questions

Conclusion

Hinged expansion joints absorb single-plane angular movement in a controlled way while carrying the pressure thrust themselves. Correctly designed as two- or three-hinge systems, they handle large thermal expansion safely. Explore bellows and connection options on our Metal Bellows Expansion Joints page, or contact the ORFA sales team for technical support.