Serrated Finned Tubes for HRSG Economizers – ASTM A335 P22
Our Serrated Finned Tubes for HRSG Economizers are designed for high-efficiency heat recovery in combined-cycle power plants, waste heat recovery boilers, and other high-temperature boiler systems. The base tube is manufactured from ASTM A335 P22, a chromium-molybdenum alloy steel developed for high-temperature service.
ASTM A335 P22 contains approximately 1.90–2.60% chromium and 0.87–1.13% molybdenum, providing a useful combination of high-temperature strength, oxidation resistance, and resistance to degradation in demanding boiler environments. ASTM specifies A335 as a seamless ferritic alloy-steel pipe specification for high-temperature service.
The serrated fin design substantially increases the external heat-transfer surface compared with a bare tube. The segmented fin profile also promotes gas turbulence, helping improve heat transfer while maintaining a practical balance between thermal performance, fouling resistance, weight, and manufacturing cost.
These tubes are particularly suitable for HRSG economizers, where hot exhaust gas transfers residual thermal energy to boiler feedwater before the water enters higher-temperature sections of the steam-generation system.
Key Features
- Base Tube Material: ASTM A335 P22 / ASME SA335 P22
- Material Type: Chromium-molybdenum alloy steel
- Fin Type: Serrated / segmented fin
- Primary Application: HRSG economizers
- Other Applications: Waste heat recovery boilers, utility boilers, industrial boilers and refinery heat-recovery systems
- Manufacturing: Finning by controlled welding or other agreed manufacturing process
- High-temperature service capability
- Excellent gas-side heat-transfer enhancement
- Good mechanical strength at elevated temperatures
- Suitable for demanding power-generation environments
- Custom tube diameter, wall thickness, fin height, pitch and length available
Typical Size Range
Actual dimensions should be selected according to the HRSG thermal design, gas velocity, pressure drop, tube-side pressure and installation requirements.
| Item |
Typical Range |
| Base Tube OD |
25.4–63.5 mm |
| Base Tube Wall Thickness |
2.5–8.0 mm |
| Overall Fin Height |
10–25 mm |
| Fin Thickness |
0.8–2.0 mm |
| Fin Pitch |
2.5–8.0 mm |
| Tube Length |
3,000–18,000 mm |
| Fin Density |
Approximately 125–400 fins/m |
| Tube Material |
ASTM A335 P22 |
| Fin Material |
Carbon steel / low-alloy steel or project-specified material |
Note: These are representative manufacturing ranges rather than fixed ASTM dimensional requirements. Final dimensions should be specified according to the purchaser's thermal and mechanical design.
ASTM A335 P22 Chemical Composition
The following composition is based on the ASTM A335 P22 requirements:
| Element |
ASTM A335 P22 Requirement, wt.% |
| Carbon (C) |
0.05–0.15 |
| Manganese (Mn) |
0.30–0.60 |
| Phosphorus (P) |
≤ 0.025 |
| Sulfur (S) |
≤ 0.025 |
| Silicon (Si) |
≤ 0.50 |
| Chromium (Cr) |
1.90–2.60 |
| Molybdenum (Mo) |
0.87–1.13 |
The chromium-molybdenum alloy system is the key reason P22 is widely used in high-temperature boiler and heat-recovery equipment.
Mechanical Properties
Typical minimum mechanical requirements for ASTM A335 P22 include:
| Property |
Requirement |
| Tensile Strength |
≥ 415 MPa |
| Yield Strength |
≥ 205 MPa |
| Elongation |
According to applicable ASTM A335 specimen and thickness requirements |
| Hardness |
According to applicable ASTM A335 requirements |
For standard P22 pipe, the commonly referenced minimum tensile strength is 415 MPa (60 ksi) and minimum yield strength is 205 MPa (30 ksi). ASTM A335 also establishes requirements concerning tensile, hardness and other mechanical testing.
Serrated Fin Design
The serrated fin consists of a continuous fin strip formed with regularly spaced cuts or slots. Compared with a plain continuous fin, this segmented configuration can disturb the boundary layer and increase gas-side turbulence.
For HRSG economizers, the design provides several advantages:
- Increased external heat-transfer area
- Improved gas-side heat transfer
- Better gas-flow mixing around the fin surface
- Reduced continuous fin thermal resistance
- Good suitability for compact heat-recovery equipment
- Practical resistance to thermal expansion and operating stresses
- Flexible optimization of fin height and pitch according to gas-side pressure-drop requirements
The fin geometry can be customized for different HRSG exhaust-gas temperatures, gas compositions, velocities and allowable pressure drops.
Manufacturing Process
Our serrated finned tubes can be manufactured through a controlled fin-forming and attachment process designed to maintain consistent fin geometry and reliable tube-to-fin contact.
Typical production steps include:
- P22 base tube inspection
- Tube surface preparation
- Fin-strip preparation
- Serration / segmentation forming
- Controlled fin attachment
- Fin pitch and height calibration
- Dimensional inspection
- Surface cleaning
- Final NDT and pressure testing
- Marking, preservation and packing
Particular attention is given to fin attachment quality because reliable thermal contact between the fin and tube is essential for maintaining heat-transfer performance throughout long-term HRSG operation.
Inspection and Testing
Quality control can include the following inspections and tests according to the applicable ASTM/ASME specification, purchase order and project requirements:
1. Chemical Analysis
Heat and/or product chemical analysis is performed to verify compliance with the specified P22 chemistry.
2. Tensile Test
Tensile testing verifies the required tensile strength, yield strength and elongation of the P22 base tube.
3. Hardness Test
Hardness testing is performed according to the applicable ASTM A335 requirements.
4. Hydrostatic Test
ASTM A335 requires each length of pipe to undergo hydrostatic testing, subject to the provisions of the specification.
5. Non-Destructive Examination
Depending on the order specification, NDT may include:
- Ultrasonic testing (UT)
- Eddy-current examination
- Magnetic particle testing (MT)
- Liquid penetrant testing (PT), where applicable
- Weld/fin attachment examination
ASTM A335 requires examination by an applicable non-destructive examination method, with the method and size limitations governed by the relevant requirements.
6. Dimensional Inspection
The following parameters are checked:
- Tube outside diameter
- Tube wall thickness
- Tube straightness
- Tube length
- Fin height
- Fin thickness
- Fin pitch
- Fin density
- Fin-to-tube attachment
- Overall finned diameter
7. Visual and Surface Inspection
The tube and fin surfaces are inspected for cracks, excessive oxidation, mechanical damage, incomplete fin attachment and other manufacturing defects.
Applications
HRSG Economizers
The primary application of these P22 serrated finned tubes is the economizer section of Heat Recovery Steam Generators (HRSGs).
In a combined-cycle power plant, the economizer recovers energy from hot gas leaving the gas-turbine exhaust/heat-recovery path and uses it to preheat boiler feedwater. This reduces the energy required in subsequent steam-generation stages and contributes to improved overall plant efficiency.
Waste Heat Recovery Boilers
They are also suitable for industrial waste heat recovery systems where high-temperature exhaust gases are available from:
- Gas turbines
- Process furnaces
- Refinery units
- Petrochemical plants
- Steel-production equipment
- Industrial combustion systems
Utility and Industrial Boilers
P22 serrated finned tubes can also be specified for selected economizer and heat-recovery sections of conventional boilers where the temperature, pressure and design conditions are appropriate.
Why Choose ASTM A335 P22?
P22 is a practical choice for demanding high-temperature service because its chromium-molybdenum alloy composition provides better elevated-temperature performance than ordinary carbon-steel tube materials.
Its combination of:
- High-temperature strength
- Chromium-assisted oxidation resistance
- Molybdenum-enhanced high-temperature performance
- Good weldability under appropriate procedures
- Compatibility with boiler and heat-recovery applications
makes it well suited to engineered HRSG economizer designs.
Applicable Standards
Depending on the project specification, our serrated finned tubes can be supplied with reference to:
- ASTM A335 / A335M – P22
- ASME SA335 – P22
- Applicable ASME Boiler and Pressure Vessel Code requirements
- Project-specific HRSG fabrication specifications
- Customer-approved drawings and inspection plans
ASTM A335 specifically covers seamless ferritic alloy-steel pipe intended for high-temperature service and includes requirements covering chemical composition, tensile properties, hardness, hydrostatic testing and non-destructive examination.
Custom Manufacturing
We can manufacture P22 serrated finned tubes according to customer drawings or thermal-design requirements, including customized:
- Tube OD and wall thickness
- Tube length
- Fin height
- Fin pitch
- Fin thickness
- Fin density
- Fin material
- Fin attachment method
- Bare ends
- Tube bending configuration
- Inspection and testing requirements
- Packaging and marking
For HRSG projects, supplying the tube dimensions and fin geometry together with the required gas temperature, tube-side pressure, gas velocity and allowable pressure drop allows the finned tube design to be optimized for the intended economizer duty.
Product Summary
ASTM A335 P22 Serrated Finned Tubes for HRSG Economizers combine a high-temperature chromium-molybdenum alloy-steel tube with an enlarged serrated heat-transfer surface. They are engineered primarily for HRSG economizers and industrial waste-heat recovery systems, where efficient heat recovery, mechanical reliability and long-term high-temperature service are essential.
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