Metal expansion joints (also called compensators) are compensating elements for thermal expansion and relative movement in pipelines, containers and machines. They consist of one or more metal bellows, connectors at both ends, and tie rods that depend on the application. They are differentiated according to the three basic types of movement: axial, angular and lateral expansion joints. Expansion joints have usage in various sectors, like energy production, paper industry, chemical industry, water treatment, oil and gas. Expansion joints can be used wherever thermal movements or vibration occurs in pipelines.
The origins Emil Witzenmann was considered the inventor of expansion joints.
In 1920, he applied for a patent for the first so-called flexible metal tube expansion joint, German Reichspatent No. 367 185, from 29 July 1920. From a technical point of view, this precursor of today's expansion joints is a large, pressure-tight flexible metal hose with a defined, restricted freedom of movement. In the 1930s, the 'metal hose' or 'flexible metal tube' principle was replaced by the metal bellows as the central functional element. This design principle – metal bellows with connection pieces – is still the structural basis of modern metal expansion joints today. However, records now show that a factory was Founding of Henri Ehrmann & Co. a factory for metal cartridges in Karlsruhe / Germany in 1872. In 1898 A patent was applied for "flexible metal tubes with beading folds" (convolutions), Production of bellows and metal hoses of seamless corrugated tubes for industrial applications, was therefore first ever manufacturer by, the company now known as, The BOA Group.
The multi-ply design In modern expansion joints, the metal bellows are often produced with a so-called multi-ply design. To increase both flexibility and stability, multiple thin plies of metal are layered to form the bellows walls. There are two basic design types: The multi-ply and the multi-walled bellows structure. The multi-ply structure consists of a pressure-tight, longitudinally welded outer and inner cylinder of stainless steel. In between these cylinders is an open, spiral cylinder which forms multiple plies depending on the design. The multi-walled structure consists of several concentric, longitudinally welded cylinders. Each cylinder forms a pressure-tight and closed "wall".
The main advantages of multi-walled bellows:
Resistance to high and very high pressures Large movement absorption Small dimensions Small adjusting force rates Optimal compensation in a very small space Early leak indication (in case of damage) via standard check hole Complete burst resistance Possibility of permanent leak monitoring in critical media Economical use of high-quality, corrosion-resistant materials such as Inconel, Incoloy, Hastelloy, titanium and Tantal Insulation against structure-borne noise up to 20 dB This design has both technical and economic advantages. For example, the bellows can be constructed of different materials, such as high-alloy stainless steels for the pipes in contact with the medium (inside and/or outside), and low-alloy stainless steels for the intermediate plies.
Compensation types
Axial
In axial compensation, the thermal expansion of a straight line section between two fixed points is absorbed by an axial expansion joint. The distance between two fixed points defines the pipeline length requiring compensation, and thus determines the axial movement that must be achieved by the expansion joint. The following basic principles apply to axial compensation:
The single-plane or multi-plane piping system is subdivided into straight sections by fixed point in such a way that each section can be compensated by a single axial expansion joint. The fixed points must be designed to withstand the pressure and spring forces of the axial expansion joint, the frictional forces of the pipe guides and the flow forces. Long pipes must be protected against kinking between the fixed points using pipe guides. The axial expansion joint should be installed in the immediate vicinity of a fixed point and a pipe guide. Impermissibly large fixed point loads can be prevented by using axial expansion joints that are relieved of pressure forces.
Angular The angular compensation of thermal expansion requires at least two, and for full compensation even three, angular expansion joints. Angular expansion joints offer a wide variety of combination options in so-called two-hinge or three-hinge systems. Single-plane three-hinged systems make do with one-sided angularly flexible expansion joints, while multi-plane three-hinged systems for absorbing thermal expansion in three axial directions require at least two gimbal expansion joints that are angularly flexible on all sides. The following basic rules apply to angular compensation:
Always at least two angular expansion joints are needed. Angular expansion joints are always associated with multiple redirections of flow by 90°. Because angular expansion joints (as hinged expansion joints) themselves absorb the compressive forces released by the bellows, the fixed points in the pipeline are only loaded by their adjusting forces and torques, by the frictional forces of the pipe guides and by the flow forces. Angular compensation is specifically designed for complex multi-plane pipework.
Lateral Lateral compensation is likewise associated with a redirection of flow by 90° within single-plane or multi-plane piping systems. Usually, lateral expansion joints are installed in existing right-angle redirections in the system. The movement of a lateral expansion joint always consists of the desired lateral movement and a slight unavoidable axial movement that comes from the expansion joint itself. Simple lateral expansion joints for lateral movements in one plane only permit a far larger expansion absorption than axial expansion joints. Lateral expansion joints that are movable in all planes simultaneously absorb expansion from two pipe sections in different directions. The following basic rules apply to lateral compensation:
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