Selection and design points of expansion joints
The expansion joint in the heat exchanger is mainly used to deal with the thermal expansion problem caused by temperature changes to ensure the safe and stable operation of the equipment.
1. The core role of expansion joints
①Compensate for thermal expansion differences
When the tube side (internal pipe) and shell side (external shell) expand or contract asynchronously due to temperature difference, the expansion joint absorbs the length difference between the two through its own flexible deformation (such as the expansion and contraction of the bellows) to avoid damage to the structure due to excessive stress.
②Reduce thermal stress
Directly relieve the internal stress of metal parts caused by temperature difference, prevent weld cracking, tube sheet deformation or shell warping, and protect key connection parts.
③Prevent leakage and structural failure
Under extreme temperature fluctuations, uncompensated expansion may cause flange seal failure or pipe rupture. The expansion joint maintains sealing by adjusting deformation and reduces the risk of medium leakage.
④Buffer vibration and displacement
In addition to thermal expansion and contraction, the expansion joint can also absorb mechanical vibration caused by fluid flow or displacement caused by equipment installation errors, thereby improving system stability.
⑤Extend equipment life
By reducing alternating stress and fatigue damage, the expansion joint indirectly reduces maintenance frequency and improves the durability and economy of the heat exchanger.
2.Differences in materials and models of expansion joints
In heat exchangers or piping systems, the material and model of the expansion joint directly affect its applicable scenarios, compensation capacity and service life.
①How to choose expansion joints of different materials
| Material | Features | Applicable scenarios | Limit |
| Stainless steel expansion joints | High temperature resistance (up to 800°C), corrosion resistance (especially suitable for acidic/alkaline media), high strength and long service life. | High-temperature and high-pressure steam pipelines, corrosive media in the petrochemical industry, nuclear power plants and other high-demand environments | The cost is higher and the flexibility is weaker than rubber. |
| Rubber expansion joints | Excellent elasticity, vibration absorption and noise reduction, easy installation, but limited temperature resistance (usually -50°C~150°C). | Low temperature water system, chemical pipeline (weakly corrosive medium), air conditioning and ventilation ducts, compensation for small displacement or vibration. | It is prone to aging and is not suitable for high temperature, high pressure or highly corrosive environments. |
| Composite expansion joints | It has both the strength of metal and the strong corrosion resistance (such as concentrated sulfuric acid and chlorine) of PTFE. | Strong acid/alkaline medium transportation pipelines, electroplating industry, special chemical reaction equipment. | The compressive resistance is weak and mechanical shock should be avoided. |
| Metal bellows expansion joint | By superimposing multiple layers of thin-wall corrugations, flexibility and pressure-bearing capacity are balanced, and the compensation amount is large. | High-pressure pipelines (such as long-distance natural gas pipelines) and thermal pipeline networks with large temperature differences. | -------------------------- |
Metal bellows expansion joint
②How to choose different types of expansion joints
| TYPE | EFFECT | APPLICATION |
| Single axial expansion joint | It only compensates for the displacement in the axial direction (straight direction) and is suitable for the simple thermal expansion of the straight section of the pipeline. | Single wave or few waves, compact structure. |
| Compound expansion joint | It can simultaneously compensate for axial, transverse (lateral) and angular displacements and adapt to complex pipeline deformations. | Multiple groups of ripples are connected in series, and the compensation ability is stronger. |
| Hinge expansion joint | Specially used to absorb angular displacement (deformation caused by pipe bending) and needs to be installed in groups. | At the corners of L-shaped or Z-shaped pipe arrangements. |
| Pressure Balance Expansion Joint | The built-in balancing structure eliminates the thrust of the medium pressure on the fixed support and protects the equipment. | Prevent thrust damage to long-distance steam pipelines, pump/valve inlets and outlets. |
| External pressure expansion joint | The bellows can withstand external pressure, has strong resistance to instability, and is suitable for vacuum or external pressure environments. | -------------- |
By rationally selecting materials and models, expansion energy saving can accurately match system requirements, ensuring equipment safety and extending its life.