What are Bi-Metallic Composite Tubes?
What Are Bi-Metallic Composite Tubes?
Bi-metallic composite tubes are advanced tubular products manufactured by bonding two distinct metals or alloys into an integrated structure. They follow a base + cladding design:
- The base layer (typically carbon steel, low-alloy steel) provides structural strength, pressure resistance and cost efficiency.
- The cladding layer (stainless steel, nickel alloy, copper, aluminum, titanium) delivers corrosion resistance, wear resistance or high thermal conductivity.
Bonding can be mechanical (interference fit) or metallurgical (atomic diffusion bonding), combining the merits of both materials while avoiding the high cost of full alloy tubes.
Common Applications of Bi-Metallic Composite Tubes
These tubes are widely used in heavy industry for harsh service conditions:
Petroleum & Petrochemical
Oil/gas gathering pipelines, sour water systems, refining reactors, handling H₂S, chloride and high-pressure corrosion.
Power & Energy
Boiler waterwalls, coal-fired heat recovery, nuclear power heat transfer circuits, balancing heat resistance and corrosion protection.
Desalination & Marine
Seawater cooling, condenser tubes, resisting saltwater and marine corrosion.
Chemical Industry
Acid/alkali pipelines, reaction vessel coils, high-temperature and corrosive medium transport.
HVAC & General Industry
Heat exchange units, food-grade sanitary pipes, waste heat recovery systems.
Application in Heat Exchanger Industry
Bi-metallic composite tubes are essential components in modern heat exchangers. They solve the conflict between structural strength and heat transfer efficiency in single-material tubes.
Typical pairings: carbon steel + stainless steel, steel + copper, steel + aluminum, alloy + nickel-based alloy.
• Higher thermal conductivity than full alloy tubes, boosting heat transfer efficiency by 30–60%.
• Excellent resistance to fouling, erosion and chloride stress corrosion.
• Lower total cost compared to pure copper or nickel alloy tubes.
Shell-and-tube heat exchangers, condensers, evaporators, air coolers, waste heat boilers in coal chemical and petrochemical plants.
How to manufacture Bi-Metallic Composite Tubes?
1. Mechanical Composite
Hydraulic Expansion: Insert inner tube into outer tube, apply high-pressure water to form interference fit. Simple, low-cost, suitable for thin-walled tubes.
Roll Bonding: Use rolling to compress layers into mechanical bonding. Stable for mass production.
2. Metallurgical Composite
Explosion Bonding: High-speed impact via controlled detonation creates atomic bonding; bonding strength >200MPa, ideal for thick-walled heavy-wall tubes.
Hot Rolling Composite: High-temperature rolling enables atomic diffusion.
Extrusion Composite: Co-extrusion of composite billets under high pressure and temperature.
3. Centrifugal Casting Composite
Molten cladding metal centrifugally cast onto the inner/outer base tube, followed by drawing or rolling. Suitable for large-diameter, thick composite tubes.
4. Welding based on Composite Plate
Take pre-manufactured bi-metallic composite plates as raw materials, cut them, form into tubular structure, and weld the seam. Flexible production, adaptable to non-standard sizes.
5. Overlay Welding
A cladding layer of required alloy deposited on the base tube via surfacing welding (submerged arc, TIG). High bond strength and excellent corrosion resistance.
How to control and make sure the quality of Bi-Metallic Composite Tubes?
Cold drawing/cold rolling to final dimensions. UT, PT, hydraulic pressure testing, bond strength and corrosion testing to ensure performance.
Regular Sizes and Dimensional Tolerances
The regular sizes of bi-metallic composite tubes are mainly determined by the application scenario. Common specifications cover small to medium diameters, with flexible adjustment according to customer needs.
| DN | D (mm) | Except pipe ends | Pipe ends | ||
|---|---|---|---|---|---|
| Seamless composite pipe | Welded composite pipe | Seamless composite pipe | Welded composite pipe | ||
| 15 | 21.3 | +0.4/-0.8 | ±0.5 | +0.4/-0.8 | ±0.5 |
| 20 | 26.9 | +0.4/-0.8 | ±0.5 | +0.4/-0.8 | ±0.5 |
| 25 | 33.7 | +0.4/-0.8 | ±0.5 | +0.4/-0.8 | ±0.5 |
| 32 | 42.4 | +0.4/-0.8 | ±0.5 | +0.4/-0.8 | ±0.5 |
| 40 | 48.3 | +0.4/-0.8 | ±0.5 | +0.4/-0.8 | ±0.5 |
| 50 | 60.3 | ±0.75% D | +1.6/-0.4 | ||
| 65 | 76.1 | ±0.75% D | +1.6/-0.4 | ||
| 80 | 88.9 | ±0.75% D | +1.6/-0.4 | ||
| 100 | 114.3 | ±0.75% D | +1.6/-0.4 | ||
| 125 | 139.7 | ±0.75% D | +1.6/-0.4 | ||
| 150 | 168.3 | ±0.75% D | +1.6/-0.4 | ||
| 200 | 219.1 | ±0.75% D or ±3.2 whichever smaller | ±0.5% D or ±1.6 whichever smaller | ||
| Parameter | Tube Type | Size Range | Tolerance |
|---|---|---|---|
| Total Thickness t | Seamless Clad Tube | t ≤ 4 | +0.6/-0.5 |
| 4 < t < 25 | +15%t / -10%t | ||
| t ≥ 25 | Upper: +3.7 or +10%t (greater); Lower: -3 or -10%t (abs greater) | ||
| Total Thickness t | Welded Clad Tube | t ≤ 5.0 | ±0.5 |
| 5 < t < 15 | ±10%t | ||
| t ≥ 15 | ±1.5 | ||
| Thickness of Clad Layer t1 | — | t1 ≤ 0.4 | +1 / -0.05 |
| 0.4 < t1 < 1.5 | +1 / -0.1 | ||
| t1 > 1.5 | +1.5 / -7.5%t1 |
Length: Standard length 6m, 9m, 12m; non-standard lengths customizable. Length tolerance: +50mm/-0mm. Straightness considered.
End Types of Bi-Metallic Composite Tubes
Plain End
Perpendicular to tube axis, mainly for welding connection. Simple and reliable, widely used in high-pressure, high-temperature systems (petrochemical, power industry).
Threaded Connection
Internal or external threads for quick connection with threaded fittings. Suitable for low-pressure, low-temperature pipelines (HVAC, general industrial).
Groove Connection
Circular groove on outer wall, uses groove clamp. Fast installation, no welding needed. Ideal for pipelines requiring frequent disassembly.
Out-of-Roundness and Curvature of Bi-Metallic Composite Tubes
Difference between max and min outer diameters. For most specifications: ≤1.5% of nominal outer diameter (D). High-precision applications (heat exchanger tubes) require stricter control. Controlled via cold drawing, sizing, straightening.
Maximum deviation from a straight line per unit length. Overall curvature ≤0.15% of length. For 6m tube: total curvature ≤6mm; >12m: ≤1.2 mm/m. Corrected by mechanical or thermal straightening.
Excessive out-of-roundness may cause assembly difficulties or sealing gaps; excessive curvature leads to installation misalignment and uneven stress distribution.