Economizer tubes form the heat-transfer surface of a boiler economizer. They recover heat from flue gas and transfer it to boiler feedwater before it enters the steam-generating system.
Preheating the feedwater improves heat recovery and reduces the temperature difference between the feedwater and the boiler system.
Economizer tubes are selected according to the boiler design, feedwater pressure and temperature, gas-side conditions and corrosion risk. Carbon steel is used where the design conditions permit; alloy or stainless steel grades may be specified for more demanding services.
Product Specifications
| Item | Description |
|---|---|
| Product | Seamless boiler economizer tubes |
| Typical material | Carbon steel; alloy grades where required by design |
| Representative grades | 20G, 20MnG, 20, SA-192, SA-210 A1/C, St35.8 and St45.8 |
| Other project-specified products | ASTM A106 Grade B/C or ASME SA-106B/C seamless pipe, where the design and order specify this product form |
| Product standards | GB/T 3087, GB/T 5310, ASTM A192/A210 or corresponding ASME SA specifications |
| 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 |
| Design form | Straight tubes or drawing-defined bends and coil or bank arrangements |
The listed grades are examples across different product standards and are not interchangeable. The selected grade must be approved for the design pressure, metal temperature and applicable boiler code.
Materials and Grade Selection
| Material family | Representative grades | Typical selection considerations |
|---|---|---|
| Carbon steel | 20G, 20MnG, SA-192, SA-210 A1/C | Common choice when temperature, pressure and corrosion conditions permit carbon steel |
| Low-alloy steel | Grade specified by the boiler design | Used where higher-temperature strength or other design requirements call for alloy steel |
| Stainless steel | Grade specified for the service | Used where the environment or design requires additional oxidation or corrosion resistance |
Material selection should account for feedwater chemistry, dissolved oxygen, pH, deposits, flue-gas temperature, acid dew-point corrosion, ash erosion and expected start-stop cycles.
No single grade is suitable for every economizer location.
Heat Recovery and Service Conditions
Flue gas passes over the outside of the tube bank while feedwater flows inside the tubes. The heat-transfer duty depends on gas and water flow, inlet temperatures, tube arrangement, surface area and fouling conditions.
Economizers may be arranged as bare-tube or extended-surface banks, depending on the design. Extended surfaces such as fins are separate features from the base tube and should be specified on the drawing.
Gas-side pressure drop, ash accumulation, soot blowing and access for cleaning are also part of the system design.
Operating conditions should maintain suitable feedwater flow through the tubes. Low-flow, startup and transient conditions need to be considered by the boiler designer to manage thermal stress and local overheating risk.
Dimensions and Delivery Requirements
Specify the outside diameter, wall thickness, length and dimensional standard. Tolerances vary with product standard, tube size and hot- or cold-finished manufacturing route.
A general size chart should not be treated as proof that every grade is available in every dimensional combination.
For bent tubes, banks or finned assemblies, provide the relevant drawings and state whether dimensions refer to the base tube, finished bend or complete assembly.
Surface condition, end preparation and protection during shipment should also be defined.
Manufacturing and Inspection
Seamless tubes are produced by piercing solid billets followed by hot working or cold finishing. Required heat treatment, finishing and inspection depend on the selected material standard and order.
Inspection requirements may include:
- Chemical analysis and heat identification.
- Tensile testing and other grade-specific mechanical tests.
- Outside diameter, wall thickness, length and straightness checks.
- Internal and external surface examination.
- Flattening, flaring or other specified technological tests.
- Hydrostatic testing and/or specified nondestructive examination.
- Additional checks for bends, fins or completed tube-bank components, where ordered.
Inspection documents should identify the standard and edition, grade, heat number, dimensions, delivery condition and applicable test results.
Traceability should be maintained for tubes used in fabricated economizer banks.
Economizer Tubes and Water Wall Tubes
Both are boiler heat-transfer tubes, but they occupy different locations and perform different duties.
| Feature | Economizer tubes | Water wall tubes |
|---|---|---|
| Location | Flue-gas path, upstream of the evaporating section | Furnace enclosure around the combustion chamber |
| Main duty | Preheat boiler feedwater using recovered flue-gas heat | Absorb furnace heat and carry the boiler working fluid |
| Key design factors | Gas-side corrosion, fouling, erosion and feedwater conditions | Furnace heat flux, circulation and tube metal temperature |
| Common material direction | Often carbon steel when design conditions permit | Carbon steel or other grades selected for water-wall pressure and heat flux |
Final material selection follows the boiler design and construction code rather than the application label alone.
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: economizer service.
- Inspection: certificate requirements and additional tests.
For bends, fins or tube-bank assemblies, provide drawings showing the configuration, dimensions, attachment details and inspection requirements.
State the boiler service and relevant design conditions so the material and product form can be checked against the project specification.