Feedwater heater tubes are heat-transfer tubes used in shell-and-tube heaters to raise boiler-feedwater temperature before the water enters the boiler. By recovering heat from extraction steam or other process streams, feedwater heaters help improve thermal efficiency and support stable plant operation.
Each feedwater heater tube order should be matched to the heater design, applicable code, and approved drawings. Material, manufacturing route, dimensions, bend geometry, and inspection scope are specified for the individual project.
Product Overview
A feedwater heater typically contains a tube bundle installed inside a pressure shell. Feedwater passes through the tubes while steam or another heating medium transfers heat on the shell side. The exact flow arrangement depends on the heater design.
Feedwater heaters are commonly grouped as:
- Low-pressure feedwater heaters, generally installed upstream of the deaerator.
- High-pressure feedwater heaters, generally installed downstream of the boiler-feed pump and upstream of the boiler.
These categories describe service and system position. They do not, by themselves, define tube material or dimensions.
Tube Configurations
U-Bend Tubes
U-bend tubes are widely used in shell-and-tube feedwater heaters. The return bend allows the tube bundle to accommodate differential thermal expansion between the tubes and shell, subject to the equipment design. Bend radius, leg length, spacing, and bend orientation should follow the approved drawing.
Straight Tubes
Straight tubes may be used where the heater design calls for straight-tube construction or where replacement requirements specify straight lengths. End preparation and tube-to-tubesheet joining details should be confirmed before manufacture.
Materials and Standards
The selected material must meet the heater designer’s requirements for pressure, temperature, water chemistry, corrosion allowance, and fabrication method. Commonly specified options may include carbon steel, alloy steel, or stainless steel, depending on the service and design.
For carbon-steel feedwater-heater tubing, ASTM A556 / ASME SA-556 is a dedicated specification that may be specified for seamless feedwater-heater tubes. Other standards, including ASTM A179 / ASME SA-179 or relevant boiler and heat-exchanger tube specifications, may be used only when permitted by the project design and purchase specification. These standards are not automatically interchangeable.
The purchase order should state the required standard and edition, grade, manufacturing method, heat-treatment condition, and any supplementary requirements. Material selection and standard compliance should be verified against the equipment data sheet and applicable construction code.
Dimensions and Manufacturing
Tube outside diameter, wall thickness, length, and tolerances are selected to suit the heater bundle and design pressure. For U-bend products, the drawing should also define bend radius, tangent points, leg dimensions, bend-plane orientation, and any limits on ovality or wall thinning.
Manufacturing and inspection requirements may include:
- Chemical composition and mechanical-property verification
- Heat treatment, when required by the material specification
- Dimensional checks before and after bending
- Visual examination of the internal and external surfaces
- Nondestructive examination and hydrostatic or other testing when required by the governing specification or purchase order
- Marking, bundling, and protection for transport
The applicable standard and approved inspection plan determine which tests are required. Additional examinations should be agreed before production.
Quality and Inspection
Feedwater heater tubes must be suitable for the specified operating conditions and fabrication process. Inspection should verify the ordered material, dimensions, surface condition, and bend geometry. For U-bend tubes, inspection criteria should address the bend and the straight legs, including the areas where forming may affect dimensions or wall thickness.
A Baosteel product manual printed in June 2007 describes super-long tubes for high- and low-pressure feedwater heaters and lists a 12–24 m range. The manual does not define the measurement basis for that range. Treat it as a historical reference only; confirm the required length definition and current manufacturing availability against the approved drawing and supplier quotation.
Applications
Feedwater heater tubes are used in:
- Utility and industrial power plants
- High-pressure and low-pressure feedwater heaters
- New heater bundle manufacturing
- Maintenance and replacement projects
Information to Include in an Inquiry
To request a quotation, please provide:
- Applicable standard, edition, grade, and material
- Tube outside diameter, wall thickness, and required length
- Straight-tube or U-bend configuration
- For U-bends: bend radius, leg lengths, bend orientation, and drawing
- Required quantity and delivery condition
- Inspection, testing, certification, and marking requirements
- Intended heater service and any project-specific technical requirements
Providing the heater drawing or tube schedule helps confirm dimensional and inspection details before production.
Frequently Asked Questions
Are feedwater heater tubes always U-bent?
No. Many shell-and-tube heater designs use U-bend tubes, but straight tubes may be specified for other designs or replacement requirements. Follow the approved equipment drawing.
Which material is suitable for a feedwater heater?
There is no single material for every heater. The designer selects the material according to operating conditions, water chemistry, code requirements, and the tube-to-tubesheet joining method. Confirm the grade and standard in the purchase specification.
Can ASTM A179 tubing replace ASTM A556 tubing?
Not automatically. They are different specifications with distinct scopes and requirements. Any substitution must be accepted by the equipment designer or purchaser and comply with the applicable code and purchase documents.
What information is needed for U-bend tube production?
At minimum, provide the tube size and material, bend radius, leg dimensions, bend orientation, tolerances, and an approved drawing. The required inspection and testing scope should also be stated.