A boiler tube coil is a pressure-containing tube fabricated into a specified bent configuration to form part of the boiler heating surface.
Depending on the boiler design, one tube can contain:
The coil geometry allows a large heat-transfer surface to be arranged within the available boiler space.
A boiler tube coil must satisfy both material and pressure-part requirements and fabrication and geometrical requirements.
The fabrication drawing is therefore one of the most important documents for quotation and production.
Economizer coils recover heat from boiler exhaust gas and transfer it to boiler feedwater.
Typical designs use serpentine or multi-bend tube arrangements installed in the boiler flue-gas path.
Material selection depends on:
Carbon steel and low-alloy steel tubes are commonly specified according to the equipment design.
Superheater coils receive saturated or partially superheated steam and increase its temperature using heat from the boiler gas path.
Compared with many economizer applications, superheater coils can experience substantially higher tube-metal temperatures.
Material selection must consider:
Carbon steel, Cr-Mo alloy steel and higher-alloy materials may be specified depending on the operating conditions.
Reheater coils heat steam returning from the turbine’s high-pressure section before it enters subsequent turbine stages.
The material and coil design are determined by:
Alloy steel grades are commonly specified for elevated-temperature reheater applications.
Evaporator or generating-bank coils transfer heat to boiler water to produce a steam-water mixture.
The required tube material, geometry and fabrication method depend on the boiler design, circulation system, pressure and temperature.
Tube coils are also used in waste heat boilers and heat-recovery systems.
These projects can involve process gases with very different:
The tube material and coil arrangement should be selected against the actual process conditions.
The base tube is the pressure-containing component of the coil.
Material selection must follow the boiler design and applicable material specification.
Typical specifications can include:
Typical applications include economizers, evaporators and other boiler pressure parts within the applicable material limits.
Typical specifications can include ASTM A213 / ASME SA-213 grades such as:
Alloy steel tubes are selected for elevated-temperature boiler components where the required strength, creep resistance or oxidation performance exceeds that of the selected carbon steel grade.
Depending on boiler design and operating conditions, austenitic stainless grades can include:
The final material must follow the equipment design, applicable boiler code and specified service conditions.
Tube bending is a critical part of boiler coil fabrication.
| Parameter | Specification |
|---|---|
| Tube Outside Diameter | According to drawing |
| Wall Thickness | According to drawing |
| Centerline Bend Radius | Custom to drawing |
| Bend Angle | According to required geometry |
| Straight Length Between Bends | According to drawing |
| Overall Coil Width & Height | Custom to drawing |
| Number of Bends | According to coil configuration |
| Developed Tube Length | According to drawing |
The bending process must control dimensional distortion while maintaining the required tube geometry and pressure-part integrity.
Bend radius should be clearly defined on the fabrication drawing. It is normally specified as Centerline Radius (CLR)or according to the applicable equipment drawing.
Tighter bend radii increase fabrication difficulty and can increase:
Minimum feasible bend radius depends on:
A universal minimum bend radius should not be applied to every boiler tube material and size.
During bending, the outside of the bend is stretched while the inside is compressed.
Critical inspection items can include:
Acceptance criteria should follow the applicable drawing, material specification, boiler code and purchase requirements.
Post-bending heat treatment depends on:
Carbon steel, Cr-Mo alloy steel and stainless steel coils do not share one universal post-bending heat-treatment requirement.
Where required, heat treatment should be performed according to the specified material and fabrication procedure.
Heat-treatment requirements should be confirmed before production rather than added automatically to every boiler coil.
Inspection can be specified according to the base tube standard, boiler code and fabrication drawing.
Available inspection items can include:
Additional NDE or third-party inspection can be arranged according to project requirements.
| Product | Typical Purchasing Information |
|---|---|
| Straight Boiler Tube | Standard + Grade + OD × WT + Length |
| Fabricated Boiler Tube Coil | Standard + Grade + OD × WT + Coil Drawing + Bend Radius + Developed Length + Inspection Requirements |
For replacement projects, matching the material and tube size alone is insufficient. The complete coil geometry must also match the existing boiler.
These products describe different features and can sometimes be combined.
| Product | Defining Feature | Typical Configurations |
|---|---|---|
| Boiler Tube Coil | Fabricated tube geometry | U-Bend / Serpentine / Multi-Bend / Custom Coil |
| Finned Tube | Extended heat-transfer surface attached to the base tube | H-Fin / Spiral Fin / Serrated Fin / Other Fin Geometry |
Depending on the boiler design, a component may be:
The correct construction should follow the thermal design and equipment drawing.
Replacement coils should be manufactured against verified dimensions rather than relying only on the original product name.
Recommended information includes:
If the original drawing is unavailable, dimensions can be taken from an existing coil or removed component.
FYN supplies custom-fabricated boiler tube coils using carbon steel, alloy steel and stainless steel tubes according to project requirements.
Typical configurations include:
| Parameter | Capability |
|---|---|
| Materials | Carbon Steel / Alloy Steel / Stainless Steel |
| Base Tube Manufacturing | Cold Drawn / Cold Rolled |
| Base Tube Outside Diameter Capability | 6–114 mm |
| Base Tube Wall Thickness Capability | 0.8–25 mm |
| Base Tube Length | Up to 40 m |
| Finished Coil Dimensions | Custom to drawing |
| Heat Treatment | According to material and fabrication requirements |
| Inspection | Dimensional / Bend Geometry / Wall Thickness / Ovality / Hydrostatic / NDT as specified |
| Documentation | MTC / Material Traceability / Inspection Records as required |
| Third-Party Inspection | Available upon request |
| MOQ | According to material, dimensions and fabrication requirements |
Finished coil dimensions depend on:
Actual fabrication capability is confirmed against the project drawing.
Available documentation can include:
Boiler tube coils require packing designed around the finished geometry.
Available arrangements can include:
Large multi-bend coils may require special packing and transportation planning to prevent deformation during shipment.
Lead time depends on material, coil geometry, quantity and inspection requirements.
For quotation, please provide:
Tube Standard & Grade + OD × WT + Coil Drawing + Bend Radius + Developed Length + Quantity
| Required Information | Details |
|---|---|
| Application | Economizer / Superheater / Reheater / Evaporator / Other Boiler Section |
| Tube Standard | Applicable material standard |
| Material Grade | Required tube grade |
| Outside Diameter | Required tube outside diameter |
| Wall Thickness | Required wall thickness |
| Coil Drawing | Fabrication or equipment drawing |
| Bend Radius | Centerline bend radius |
| Bend Angles | Required angles |
| Straight Lengths | Lengths between bends |
| Overall Dimensions | Finished coil dimensions |
| Developed Length | Required developed tube length |
| Quantity | Required order quantity |
| Design Pressure | Applicable design pressure |
| Design Temperature | Applicable design temperature |
| Operating Medium | Fluid inside the tube |
| Heat Treatment | Applicable heat-treatment requirements |
| Testing | Hydrostatic / NDT requirements |
| End Preparation | Required connection and end details |
| Documentation | Inspection documentation requirements |
| Third-Party Inspection | If required |
| Delivery | Delivery destination |
For replacement coils, send the existing drawing, MTC or dimensional information from the original coil for review.
For an accurate quotation, please send:
Tube Standard & Grade + OD × WT + Coil Drawing + Bend Radius + Developed Length + Quantity
For boiler projects, please also provide:
Application + Design Pressure + Design Temperature + Operating Medium + Inspection Requirements
For replacement projects, send the existing drawing, MTC or original coil dimensions for technical review.
