I. Structural Composition

The compensator consists of:

External pressure bellows: Wave structure facing outward, with the pressure acting from the outside to the inside.

Pressure-retaining sleeve: Encloses the bellows to withstand external pressure.

End connections: Flanges or weld ends for pipeline integration.

Guide brackets: Maintain axial movement and prevent lateral deflection.

II. Core Working Mechanism

Pressure Transmission Path

When internal pipeline medium expands (e.g., thermal elongation), the bellows is subjected to axial tensile force.

External pressure (from the sleeve) counteracts the internal expansion force, allowing the bellows to deform axially.

Displacement Compensation Process

Thermal expansion scenario:

Pipeline length increases by ΔL due to temperature rise.

External pressure forces the bellows to expand axially, absorbing ΔL through wave elongation.

Schematic formula:

ΔL=n×δ 

axial

n

: Number of bellows waves

δ 

axial

: Axial displacement per wave

III. Pressure Balance Mechanism

Key feature: The external pressure design converts internal pressure thrust into compressive force on the bellows, eliminating axial thrust on the pipeline.

Force analysis:

Internal pressure 

P

 generates axial thrust 

F=P×A 

eff

 (where 

A 

eff

 is effective area).

External pressure sleeve counteracts 

F

, ensuring net force on the pipeline is zero.

IV. Operational Advantages

Feature Mechanistic Benefit

No pipeline thrust External pressure balances internal force, eliminating the need for anchor supports.

High compensation capacity Axial deformation of multiple waves allows large displacement absorption (e.g., 200–500 mm).

Anti-fatigue design External pressure reduces stress concentration compared to internal pressure types.

V. Engineering Application Example

Scenario: A 200°C steam pipeline (DN300, L=80m, carbon steel) with ΔT=180°C.

Calculation:

Thermal displacement: 

ΔL=12×10 

−6

 ×80×180=172.8mm

.

External pressure bellows with 12 waves, each wave allowing 15 mm axial displacement:

Total compensation=12×15=180mm≥172.8mm.

Installation: Use guide supports every 10–15m to maintain axial movement, eliminating fixed anchors.

VI. Design Considerations

External pressure rating: Must exceed maximum operational pressure to prevent bellows collapse.

Guide system: Rigid guides ensure pure axial displacement, avoiding lateral loads.

Pressure test: Hydrostatic testing at 1.5× working pressure to verify structural integrity.

This design leverages external pressure to balance internal forces, enabling efficient axial compensation while minimizing pipeline stress and support requirements.