| Type | Structural Features | Typical Application Scenarios | Performance Parameters |
|---|
| U-type Bellows | U-shaped arc crests, single wave height 5-50mm, wave pitch 10-100mm, formed by hydraulic bulging or mechanical rolling. | Low-pressure pipelines (≤1.6MPa), thermal compensation (e.g., heating pipeline temperature difference compensation), shock absorption for pump/valve inlets/outlets. | Axial compensation ≤20mm/wave, pressure resistance ≤2.5MPa, fatigue life ≥1000 cycles. |
| Ω-type Bellows | Ω-shaped (double arc structure), thicker wall (1.5-3mm), higher rigidity, formed by die pressing or welding. | High-pressure systems (2.5-10MPa), nuclear power plant steam pipelines, petrochemical high-pressure pipelines. | Axial compensation ≤10mm/wave, pressure resistance ≤10MPa, fatigue life ≥5000 cycles. |
| C-type Bellows | C-shaped open crests, single wave height 2-15mm, commonly used in thin-layer stacking (2-5 layers). | Instrument measurement (e.g., pressure sensors), small-diameter gas pipelines (DN≤50), micro-displacement compensation. | Axial compensation ≤5mm/wave, pressure resistance ≤1.0MPa, high precision (displacement linearity ≤±0.5%). |
| Annular Bellows | Annular nested corrugations, welded by multiple metal diaphragms, wall thickness only 0.1-0.5mm. | Vacuum systems (e.g., vacuum furnace pipelines), aerospace fuel pipelines (lightweight, high sealing requirement). | Vacuum degree ≤10⁻⁶Pa, pressure resistance ≤0.5MPa, compensation ≤3mm (overall). |
- Single-layer Bellows:
- Structure: Single metal layer (wall thickness 0.3-2mm), simple forming, low cost.
- Application: Common media (water, air), low pressure (≤1.6MPa), non-corrosive environments (e.g., building water supply/drainage).
- Multi-layer Bellows:
- Structure: 2-10 metal layers (commonly 3-5 layers), separated by isolation layers (e.g., PTFE).
- Advantages: Pressure resistance increased by 30%-50% (e.g., 3-layer 304 stainless steel withstands 4.0MPa), fatigue resistance enhanced (life extended by 2-3 times), suitable for vibrating environments (e.g., compressor pipelines).
| Material Type | Typical Grade | Temperature Range | Corrosion Resistance | Typical Applications |
|---|
| Austenitic Stainless Steel | 304/316L | -200℃~650℃ | Resistant to acids, alkalis, salt spray (316L resists chloride corrosion), suitable for chemical and seawater desalination. | Seawater pipelines, acid-alkali solution transportation, food-grade pipelines (304 meets FDA standards). |
| Copper Alloy | H62 Brass/Copper | -100℃~250℃ | Resistant to atmospheric corrosion, good electrical conductivity, easy to weld. | Instrument signal pipelines, refrigeration systems (copper for air conditioning tube compensation). |
| Nickel-based Alloy | Inconel 625/Hastelloy C-276 | -270℃~1093℃ | Resistant to strong acids (e.g., sulfuric acid, hydrochloric acid), high temperature/pressure, suitable for harsh chemical environments (e.g., hydrometallurgy). | Concentrated hydrochloric acid pipelines (Hastelloy C-276), high-temperature steam (Inconel 625). |
| Titanium Alloy | TA2/TC4 | -253℃~500℃ | Resistant to seawater and chlor-alkali corrosion, low density (only 57% of steel). | Marine engineering, chlor-alkali chemical (electrolyzer pipelines), aviation fuel pipelines. |
- Working Pressure Calculation
- Formula: Maximum allowable pressure = material yield strength × 0.6 ÷ safety factor (usually 2.5)
- Example: 304 stainless steel (yield strength 205MPa) single-layer bellows allowable pressure = 205 × 0.6 ÷ 2.5 ≈ 49.2MPa (practically limited by structure, usually ≤10MPa).
- Temperature Adaptability
- Low-temperature scenarios (e.g., LNG pipeline -162℃) require 304L/316L stainless steel or titanium alloy;
- High-temperature (≥500℃) needs nickel-based alloys (e.g., Inconel 600) with thermal insulation (ceramic fiber wrapping).
- Axial Displacement: Linear displacement from pipeline thermal expansion/contraction (e.g., 100m carbon steel pipeline expands ~6mm at 50℃ temperature difference, requiring 1 U-type wave for compensation);
- Lateral Displacement: Sideways displacement from pipeline support offset or vibration (needs flexible multi-layer bellows, compensation ≤1% of pipe diameter);
- Angular Displacement: Pipeline interface angle deviation (e.g., installation error ≤3°, requires deflectable Ω-type or annular structure).
- Corrosive Media:
- Seawater/chloride-containing solutions: Choose 316L stainless steel (resists Cl⁻ concentration ≤2000ppm) or Hastelloy C-276;
- Concentrated nitric acid (≥65%): Choose 304 stainless steel (passivation film resists oxidizing acids), avoid 316L (molybdenum accelerates corrosion).
- Flammable/Explosive Media: Require metal layer welding tightness ≥10⁻⁹Pa·m³/s (e.g., hydrogen pipelines use vacuum electron beam welded bellows).
- Space Constraints:
- Narrow spaces (e.g., marine pipelines) choose thin C-type bellows (axial length ≤50mm);
- Outdoor installation requires weather-resistant coating (e.g., fluorocarbon paint, salt spray resistance ≥5000h).
- Vibration Frequency:
- High-frequency vibration (≥100Hz) selects multi-layer structure (damping effect reduces resonance), and calculate natural frequency (needs to avoid equipment vibration frequency ±20%).
| Scenario | Recommended Type | Selection Basis | Parameter Example |
|---|
| Heating Pipeline Thermal Compensation | U-type 304 Stainless Steel Multi-layer Bellows | Temperature difference 100℃, axial displacement 20mm/100m, pressure 1.0MPa, needs to resist water hammer (compensation +15% safety margin). | DN200, 3-layer 304, wave height 30mm, compensation 30mm, pressure resistance 1.6MPa. |
| High-temperature Pipeline in Petroleum Cracking Unit | Ω-type Hastelloy C-276 Single-layer Bellows | Medium temperature 600℃, pressure 4.0MPa, contains H₂S (≤100ppm), needs high-temperature sulfidation corrosion resistance. | DN150, wall thickness 2.5mm, wave pitch 50mm, temperature resistance 650℃, pressure resistance 6.3MPa. |
| Ultrapure Water Pipeline in Semiconductor Wafer Factory | Annular 316L Stainless Steel Bellows | Water quality requires conductivity ≤0.1μS/cm, needs mirror polishing (Ra≤0.2μm), avoids particle contamination. | DN25, single-layer 316L, inner wall electropolished, vacuum degree ≤10⁻⁴Pa, meets SEMI standards. |
| LNG Storage Tank Inlet/Outlet Pipeline | C-type Titanium Alloy Multi-layer Bellows | Temperature -196℃, prevents low-temperature embrittlement, needs lightweight design (titanium alloy density only 57% of steel). | DN80, 5-layer TA2, wave height 10mm, compensation 15mm, low-temperature resistance -253℃. |
- Parameter Determination:
- Medium type (liquid/gas), pressure, temperature, flow rate;
- Pipeline displacement (axial/lateral/angular, considering thermal expansion + mechanical vibration superposition).
- Preliminary Selection:
- Select structure by pressure (U-type for low pressure, Ω-type for high pressure), select material by temperature (titanium alloy for low temperature, nickel-based alloy for high temperature).
- Verification Calculation:
- Fatigue life calculation: N = (Δσ₀/Δσ)³ (Δσ₀ is material fatigue limit, Δσ is working stress amplitude);
- Sealing verification: Helium mass spectrometry leak detection (leakage rate ≤10⁻⁸Pa·m³/s for flammable/explosive media).
- Avoid Overpressure Use: For example, the fatigue life of 304 stainless steel single-layer bellows drops from 1000 cycles to 200 cycles under 2.5MPa pressure;
- Prohibit Medium-Material Conflict: For example, 316L stainless steel used in hydrofluoric acid (HF) medium will cause intergranular corrosion, should switch to Monel alloy;
- Installation Direction Attention: Axial bellows need to be installed axially, lateral types should keep wave crests perpendicular to the displacement direction, otherwise compensation efficiency decreases by over 50%.
| Comparison Item | Metal Bellows | Rubber Flexible Connector | Sleeve Compensator |
|---|
| Compensation Capability | Full compensation for axial/lateral/angular | Mainly angular compensation (≤15°) | Mainly axial compensation (50-200mm) |
| Temperature Range | -270℃~1093℃ | -40℃~200℃ (FKM rubber) | -50℃~400℃ (needs thermal insulation) |
| Corrosion Resistance | Wide selection of metal materials | Rubber susceptible to oil/solvent corrosion | Carbon steel needs anti-corrosion coating (life ≤5 years) |
| Cost | High (DN100 ~800-1500 CNY) | Low (DN100 ~100-300 CNY) | Medium (DN100 ~300-800 CNY) |
| Suitable Scenarios | High temperature/pressure/corrosion/precision systems | Low pressure/normal temperature/shock absorption needs | Large displacement/non-corrosive thermal pipelines |
Conclusion: The selection of metal bellows should be based on 'operating parameters as the foundation, structural materials as the core, and compensation requirements as the guide'. Through precise calculation of the coupling effect of pressure-temperature-displacement, combined with medium characteristics and installation environment, the optimal structure type and material combination are selected. For critical systems (e.g., nuclear power, aerospace), additional finite element analysis (FEA) and burst tests (1.5× design pressure) are required to ensure safety redundancy.
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