What is an expansion joint? What is the function of an expansion joint?

Release time:

2021-11-12

An expansion joint is a flexible compensating component that boasts advantages such as operational reliability, superior performance, and a compact structural design. It is widely used in fundamental engineering fields including chemical processing, construction, water supply, drainage, petroleum, light industry, refrigeration, sanitation, water temperature control, fire protection, and power generation, playing an important role in people's daily lives. So, what exactly is an expansion joint?

What is an expansion joint? What is the function of an expansion joint?

An expansion joint is a flexible compensating component that boasts advantages such as operational reliability, superior performance, and a compact structural design. It is widely used in fundamental engineering fields—including chemical processing, construction, water supply, drainage, petroleum, light industry, refrigeration, sanitation, water temperature control, fire protection, and power generation—and plays an important role in people's daily lives. So, what exactly is an expansion joint?

　　Expansion joints, also commonly referred to as compensators, are flexible structures installed on vessel shells or pipelines to absorb additional stresses caused by temperature differences and mechanical vibrations. Expansion joints are categorized into two types: metallic and non-metallic.

Expansion joints used on vessels come in various forms. In terms of corrugation shape, U-shaped expansion joints are widely used, followed by S-shaped and C-shaped ones. Regarding structural compensation, expansion joints used in piping systems are categorized into universal-type, pressure-balanced type, hinge-type, and universal joint-type.

Next, let’s join me in comparing the performance differences between metallic and non-metallic expansion joints, so that we can gain a deeper understanding of the key points related to them.

　　1. Compensation Function: Under the same external dimensions, non-metallic components exhibit a significantly greater compensation capability than metallic ones. In particular, when it comes to compensating for lateral displacement, the compensation capacity of non-metallic components is nearly one order of magnitude greater than that of metallic expansion joints.

　　2. Compensatory Resistance: After an expansion joint—acting like an elastomer—contracts or stretches, it generates resistance. Metals exhibit greater resistance than nonmetals. This excessive resistance is detrimental to the system and can damage nearby equipment.

　　3. High-Temperature and Corrosion Resistance: The materials used in non-metallic expansion joints not only exhibit high-temperature resistance but also possess acid and alkali resistance. Ordinary carbon structural steel has a yield strength of zero at 600°C, and its strength further decreases with higher temperatures due to oxidation. Carbon steel expansion joints tend to crack easily during operation, while stainless steel expansion joints are prone to low-leakage-point corrosion in low-temperature environments; moreover, their price is quite substantial.

　　4. Thermal Insulation and Energy-Saving Performance: Non-metallic structures inherently possess thermal insulation properties. Metals do not have this capability; therefore, to achieve thermal insulation, a layer of thermal insulation is applied over the exterior of metal expansion joints.

　　5. Maintainability and Replacement Performance: Non-metallic expansion joints require no maintenance throughout their normal service life. Replacing non-metallic expansion joints is much easier than replacing metallic ones.

　　6. Service Life: The service life of expansion joints is closely related to environmental conditions. Non-metallic expansion joints exhibit better wear resistance and internal food safety. Under comparable conditions, the service life of non-metallic expansion joints is longer than that of metallic expansion joints.

　　7. Operating Pressure: The flexible design and special materials used enable non-metallic expansion joints to withstand higher operating pressures.

　　8. Media Compatibility: Metal expansion joints are suitable for liquids, gases, and powders. Non-metallic expansion joints can handle both gases and liquids.

As an important category of non-metallic expansion joints, rubber expansion joints offer significant displacement compensation capabilities for axial, lateral, and angular movements, while also reducing noise, minimizing vibration, and providing corrosion resistance.

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