I. Basic Parameter Overview

II. Core Materials and Selection Points

1. Bellows Materials
   • 304 Stainless Steel: Suitable for general corrosive media (water, steam), temperature ≤300°C, cost-effective.
   • 316L Stainless Steel: Excellent chloride resistance, ideal for seawater, salt spray, or chemical media (e.g., acidic solutions).
   • Hastelloy C-276: Resistant to strong corrosion (concentrated acids, alkalis, wet chlorine), suitable for harsh chemical conditions, temperature ≤550°C.
   • Inconel 625 (Nickel-based Alloy): For high-temperature/high-pressure environments (steam pipelines, hot oils), temperature ≤650°C.
2. Flange Materials
   • Carbon Steel (Q235B, 20#): For non-corrosive media, requires anti-corrosion treatment (galvanizing, painting).
   • Stainless Steel (304, 316L): Matches bellows material for corrosive media, prevents electrochemical reactions.
   • Copper Alloy (Brass): For seawater pipelines, paired with cathodic protection (zinc anodes).

III. Structural Types and Application Scenarios

IV. Key Design and Installation Parameters

1. Compensation Calculation
   • Axial compensation (ΔL) = linear expansion coefficient (α) × pipeline length (L) × temperature difference (ΔT)
   • Example: DN100 carbon steel pipe (α=12×10⁻⁶/°C), L=50m, ΔT=80°C:$\Delta L=12\times 10^{-6}\times 50\times 1000\times 80=48\text{mm}(\text{select compensator with axial compensation}\ge 50\text{mm})$
2. Support Arrangement Requirements
   • Fixed Supports: Install 10–15 pipe diameters from both ends of the compensator to bear medium pressure thrust and compensation reaction force.
   • Guide Supports: Install 1–2 pipe diameters from the compensator to limit lateral displacement and ensure smooth axial compensation.
   • Example: For DN100 compensator, fixed supports ≤15m apart; guide supports ≤1.5m apart.
3. Pressure Resistance and Fatigue Life
   • Design pressure ≥ 1.1× maximum operating pressure; fatigue life typically required ≥1000 cycles (≥5000 cycles for chemical industry).

V. Industry Application Cases and Selection Recommendations

1. Chemical Pipeline (Medium: Hydrochloric Acid, T=80°C)
   • Bellows: 316L stainless steel (chloride resistance); Flanges: 316L + PTFE coating; Axial compensation: 15mm (thermal expansion); Equip with limit devices to prevent over-displacement.
2. Seawater Pipeline (DN100, Salinity 3.5%)
   • Bellows: 316L stainless steel (seawater resistance); Flanges: 316L + zinc anode protection; Structure: Axial type + waterproof sealant; Regularly inspect anti-corrosion layers.
3. Steam Pipeline (P=1.6MPa, T=250°C)
   • Bellows: 321 stainless steel (temperature/Intergranular corrosion resistance); Structure: Multi-layer U-wave (compensation 20mm); Connection: Welding + metal graphite gasket; Install with 1° slope to prevent condensate accumulation.

VI. Standards and Compliance References

• Domestic Standards:
  GB/T 12777-2019 General Technical Conditions for Metal Bellows Expansion Joints
  GB/T 14525-2010 Bellows Compensators
• International Standards:
  EJMA (Expansion Joint Manufacturers Association) Standards
  ASME B31.3 (Process Piping Code)

VII. Selection Considerations

1. Medium Characteristics: Clarify corrosivity, temperature, pressure, and particulates to avoid material-reaction (e.g., chloride-induced stress corrosion in 304 stainless steel).
2. Installation Space: Lateral/angular compensators need sufficient clearance; avoid forced installation deforming bellows.
3. Additional Devices: High-pressure applications require limit bolts (displacement ≤±5mm); vibrating pipelines need anti-vibration supports.
4. Fatigue Life: Frequent thermal cycles (intermittent operation) require high-fatigue models (≥10,000 cycles).