Plain boiler tubes are tubes with a smooth bore and a plain external profile, without intentionally formed internal helical ribs or external fins. They are used in boiler heating surfaces such as water walls, economizers, superheaters and reheaters.
This product category covers seamless tubes made from carbon steel, molybdenum steel, chromium-molybdenum alloys, chromium-molybdenum-tungsten alloys and austenitic stainless steel. The material grade and dimensions are selected according to the boiler design and operating conditions.
Product Specifications
| Item | Description |
|---|---|
| Product | Plain seamless boiler tubes |
| Tube profile | Smooth bore and plain external profile |
| Materials | Carbon steel, low-alloy steel and austenitic stainless steel |
| Manufacturing route | Hot-finished or cold-finished seamless tubes |
| Dimensions | Outside diameter × wall thickness × length |
| Delivery condition | Heat treatment and surface condition according to the selected grade and standard |
| Principal applications | Water walls, economizers, superheaters and reheaters |
“Plain” describes the tube profile. Surface finish, end preparation, heat treatment and dimensional tolerances remain separate order requirements. A smooth bore does not establish a polished finish or a particular surface roughness value.
Materials and Grades
| Material family | Representative grades or products | Product standards |
|---|---|---|
| Carbon steel | 10, 20 | GB/T 3087 |
| Carbon steel | 20G, 25MnG | GB/T 5310 |
| Carbon steel | ASTM A192 / ASME SA-192 tubes | ASTM A192 or ASME SA-192 |
| Carbon-manganese steel | A1, C | ASTM A210 or ASME SA-210 |
| Molybdenum steel | 15MoG, 20MoG; T1, T1a, T1b | GB/T 5310; ASTM A209 or ASME SA-209 |
| Chromium-molybdenum alloy steel | 15CrMoG, 12Cr1MoVG; T11, T22, T24, T91 | GB/T 5310; ASTM A213 or ASME SA-213 |
| Chromium-molybdenum-tungsten alloy steel | T23, T92, T911, T122 | ASTM A213 or ASME SA-213 |
| Austenitic stainless steel | TP304H, TP321H, TP347H, UNS S30432, TP310HCbN | ASTM A213 or ASME SA-213 |
Standards apply to the corresponding grades within each row. Grade coverage, designation and acceptance requirements should be checked against the specified edition. Similar applications do not establish equivalence between different grades or standards.
Dimensions and Delivery Condition
Specify the outside diameter, wall thickness basis and required length. Available dimensional combinations depend on the material and manufacturing route; a size range for one product should not be assumed to apply to every grade.
Hot finishing and cold finishing provide different processing routes. Final heat treatment depends on the material specification. Requirements for straightness, ovality, tube ends and surface condition should be included in the purchase specification where applicable.
Mechanical Properties
Plain boiler tubes do not share one chemical composition or strength specification. Tensile strength, yield strength, elongation and hardness requirements follow the selected material grade and standard.
For elevated-temperature service, material selection must also consider allowable stress, creep behavior and oxidation. Tube geometry alone does not determine the permitted operating pressure or temperature.
Applications
Water Wall Tubes
Plain tubes are used in boiler water wall circuits to carry water or a steam-water mixture and absorb furnace heat. Selection depends on the circulation system, heat flux, pressure and tube metal temperature.
Economizer Tubes
Economizers recover heat from flue gas to preheat boiler feedwater. Carbon steel plain tubes are used where the design permits, with tube dimensions and service allowances selected for the pressure, water chemistry, corrosion and erosion conditions.
Superheater Tubes
Superheater tubes carry steam as its temperature rises above saturation. Alloy steel or austenitic stainless steel grades are selected where their elevated-temperature properties satisfy the design requirements.
Reheater Tubes
Reheater tubes heat steam between turbine stages. Grade selection should account for temperature, pressure, thermal cycling and expected operating life.
Plain Tubes and Internally Rifled Tubes
| Feature | Plain boiler tubes | Internally rifled boiler tubes |
|---|---|---|
| Internal geometry | Smooth bore without intentionally formed ribs | Internal helical ribs |
| Design parameters | Diameter, wall thickness and material | Diameter, wall thickness, material and rib geometry |
| Typical applications | Water walls, economizers, superheaters and reheaters, depending on grade | Selected water wall circuits |
| Heat-transfer considerations | Flow conditions and tube geometry | Flow conditions, tube geometry and the influence of internal ribs |
Internally rifled tubes can improve heat transfer in suitable operating conditions by influencing flow inside the tube. The choice between plain and rifled tubes should follow the boiler’s thermal and hydraulic design.
Manufacturing and Inspection
Seamless tubes are produced by piercing solid billets and subsequent hot working or cold finishing. Required heat treatment is followed by finishing and inspection.
Depending on the standard and order, inspection may include:
- Chemical analysis and tensile testing.
- Outside diameter, wall thickness, length and straightness checks.
- Internal and external surface inspection.
- Flattening, flaring or other specified technological tests.
- Hydrostatic testing and/or specified nondestructive examination.
- Hardness, grain-size or additional tests where required for the selected grade.
Inspection documents should identify the grade, product standard, heat number, dimensions, delivery condition and applicable test results. Traceability should be maintained through cutting and fabrication.
Ordering Information
For a quotation, specify:
- Material grade: required carbon steel, alloy steel or stainless steel grade.
- Standard: product standard and edition.
- Dimensions: outside diameter, wall thickness and length.
- Wall thickness basis: as required by the selected standard.
- Quantity: number of tubes, total length or weight.
- Delivery condition: heat treatment and surface condition.
- Tube ends: required end preparation.
- Application: water wall, economizer, superheater or reheater.
- Inspection: certificate requirements and additional tests.
For further fabrication, provide drawings and requirements for bending, welding or attachment of external components.