Water wall tubes form the heat-absorbing surfaces around a boiler furnace. They carry the working fluid and absorb heat, primarily by radiation from the combustion zone. In evaporating sections of subcritical boilers, the fluid may be water or a steam-water mixture; once-through boilers have different flow conditions according to their design and operating pressure.
Water walls may use plain or internally rifled tubes. The material, tube dimensions and internal geometry are selected to suit the boiler’s pressure, heat flux, circulation system and tube metal temperature.
Product Specifications
| Item | Description |
|---|---|
| Product | Seamless tubes for boiler water walls |
| Tube profiles | Plain or internally rifled |
| Material families | Carbon steel, carbon-molybdenum steel and selected alloy steels |
| Dimensions | Outside diameter × wall thickness × length |
| Delivery condition | Heat-treated according to the selected grade and product standard |
| Fabrication forms | Straight tubes or drawing-defined bent tubes; panel requirements specified separately |
| Principal applications | Furnace water walls in power-generation and industrial boilers |
Tube dimensions, tolerances and surface requirements should follow the specified standard and order. For internally rifled tubes, the drawing must also define the internal rib geometry and wall thickness measurement basis.
Materials and Standards
| Material family | Representative products or grades | Product standards |
|---|---|---|
| Carbon steel | 20G, 25MnG | GB/T 5310 |
| Carbon steel | ASTM A192 / ASME SA-192 tubes | ASTM A192/A192M or ASME SA-192/SA-192M |
| Carbon-manganese steel | A1, C | ASTM A210/A210M or ASME SA-210/SA-210M |
| Carbon-molybdenum steel | 15MoG, 20MoG | GB/T 5310 |
| Selected alloy steels | 15CrMoG; T2, T12 | GB/T 5310; ASTM A213/A213M or ASME SA-213/SA-213M, respectively |
These grades represent material options for appropriate designs. The handbook lists 15CrMoG, T2 and T12 among its internally rifled tube materials. Suitability for a particular water wall must be established by the boiler design rather than inferred from inclusion in a material list.
Chemical composition, tensile properties, heat treatment and allowable stresses vary by grade. The purchase specification should identify the product standard and edition; materials from different standards should not be assumed equivalent.
Tube Profiles and Water Wall Construction
Plain Water Wall Tubes
Plain tubes have a smooth bore without intentionally formed internal helical ribs. They are used where the boiler’s thermal and hydraulic design permits this profile. Diameter, wall thickness, tube arrangement and flow conditions influence heat transfer and pressure drop.
Internally Rifled Water Wall Tubes
Internally rifled tubes contain helical ribs that influence fluid flow and can improve heat transfer under suitable conditions. In applicable evaporating circuits, this can help reduce the risk of heat-transfer deterioration associated with steam formation.
Rib count, height, helix angle and other profile dimensions must be specified. The benefit depends on pressure, flow rate, heat flux and rib geometry; internally rifled tubes are not a universal replacement for plain tubes.
Membrane Water Walls
Membrane water walls are panels made by joining adjacent tubes with welded membrane strips or fins to form a substantially gas-tight furnace enclosure. A membrane panel can use either plain or internally rifled tubes: the panel construction and internal tube profile are separate design choices.
Panel fabrication requires drawings defining tube pitch, membrane dimensions, bends, openings, weld details and connection points. Tube material certification alone does not establish compliance of the completed panel.
Design and Service Considerations
Water wall performance depends on both heat absorption and adequate internal cooling. Material selection and tube sizing should consider:
- Design pressure and tube metal temperature.
- Furnace heat flux and local heat distribution.
- Circulation, mass flow and pressure drop.
- Water chemistry, internal deposits and corrosion.
- External corrosion, erosion and ash exposure.
- Thermal expansion, cycling and welded connections.
Deposits can reduce heat transfer and increase tube metal temperature. Appropriate water treatment, inspection and maintenance remain essential for service performance.
Manufacturing and Inspection
Seamless tube manufacture includes piercing, hot working or cold finishing, required heat treatment and final inspection. Bending, membrane welding and panel assembly are additional fabrication operations governed by the construction code and project specification.
Depending on the order, inspection may include:
- Chemical analysis, tensile testing and material traceability.
- Outside diameter, wall thickness, length and surface checks.
- Internal rib measurements for rifled tubes.
- Hydrostatic testing and/or specified nondestructive examination.
- Bend geometry and remaining wall thickness checks.
- Weld inspection and panel dimensional checks where panels are ordered.
- Heat-treatment records and additional tests where required.
The order should distinguish tests required for the original tubes from those required after bending, welding or panel assembly.
Ordering Information
For a quotation, specify:
- Material: grade, product standard and edition.
- Tube profile: plain or internally rifled.
- Dimensions: outside diameter, wall thickness basis and length.
- Quantity: number of tubes, total length or weight.
- Delivery condition: required heat treatment and surface condition.
- Inspection: certificate requirements and additional tests.
- Drawings: bend dimensions, rib geometry or panel layout, as applicable.
For replacement tubes or fabricated panels, provide drawings showing tube pitch, bend radii, rib geometry where applicable, connections and dimensional tolerances. Any change of grade, profile or dimensions should be reviewed against the boiler design requirements.